Google Git
Sign in
apache / pulsar-site / refs/heads/asf-site-next / . / content / docs / 3.0.x / client-libraries-readers / index.html
blob: f3d4a35317aea64fe763c5958530cb6a83eac2d1 [file] [log] [blame]
<!doctype html>
<html lang="en" dir="ltr" class="docs-wrapper docs-doc-page docs-version-3.0.x plugin-docs plugin-id-default docs-doc-id-client-libraries-readers">
<head>
<meta charset="UTF-8">
<meta name="generator" content="Docusaurus v2.4.0">
<title data-rh="true">Work with reader | Apache Pulsar</title><meta data-rh="true" name="viewport" content="width=device-width,initial-scale=1"><meta data-rh="true" name="twitter:card" content="summary_large_image"><meta data-rh="true" property="og:image" content="https://pulsar.apache.org/img/pulsar-social-media-card.png"><meta data-rh="true" name="twitter:image" content="https://pulsar.apache.org/img/pulsar-social-media-card.png"><meta data-rh="true" property="og:url" content="https://pulsar.apache.org/docs/3.0.x/client-libraries-readers/"><meta data-rh="true" name="docusaurus_locale" content="en"><meta data-rh="true" name="docsearch:language" content="en"><meta data-rh="true" name="docusaurus_version" content="3.0.x"><meta data-rh="true" name="docusaurus_tag" content="docs-default-3.0.x"><meta data-rh="true" name="docsearch:version" content="3.0.x"><meta data-rh="true" name="docsearch:docusaurus_tag" content="docs-default-3.0.x"><meta data-rh="true" property="og:title" content="Work with reader | Apache Pulsar"><meta data-rh="true" name="description" content="After setting up your clients, you can explore more to start working with readers."><meta data-rh="true" property="og:description" content="After setting up your clients, you can explore more to start working with readers."><link data-rh="true" rel="icon" href="/img/favicon.ico"><link data-rh="true" rel="alternate" href="https://pulsar.apache.org/docs/3.0.x/client-libraries-readers/" hreflang="en"><link data-rh="true" rel="alternate" href="https://pulsar.apache.org/docs/3.0.x/client-libraries-readers/" hreflang="x-default"><link data-rh="true" rel="canonical" href="https://pulsar.apache.org/docs/client-libraries-readers/"><link data-rh="true" rel="preconnect" href="https://WK2YL0SALL-dsn.algolia.net" crossorigin="anonymous"><link rel="alternate" type="application/rss+xml" href="/blog/rss.xml" title="Apache Pulsar RSS Feed">
<link rel="alternate" type="application/atom+xml" href="/blog/atom.xml" title="Apache Pulsar Atom Feed">
<link rel="search" type="application/opensearchdescription+xml" title="Apache Pulsar" href="/opensearch.xml">
<link rel="stylesheet" href="/css/katex-0.13.24.min.css" media="print" onload="this.media=&#39;all&#39;">
<script src="/js/sine-waves.min.js" async></script>
<script src="/js/matomo-agent.js"></script><link rel="stylesheet" href="/assets/css/styles.83bad5a1.css">
<link rel="preload" href="/assets/js/runtime~main.f1ab6cb0.js" as="script">
<link rel="preload" href="/assets/js/main.9801eec2.js" as="script">
</head>
<body class="navigation-with-keyboard">
<script>!function(){function t(t){document.documentElement.setAttribute("data-theme",t)}var e=function(){var t=null;try{t=new URLSearchParams(window.location.search).get("docusaurus-theme")}catch(t){}return t}()||function(){var t=null;try{t=localStorage.getItem("theme")}catch(t){}return t}();t(null!==e?e:"light")}(),document.documentElement.setAttribute("data-announcement-bar-initially-dismissed",function(){try{return"true"===localStorage.getItem("docusaurus.announcement.dismiss")}catch(t){}return!1}())</script><div id="__docusaurus">
<div role="region" aria-label="Skip to main content"><a class="skipToContent_fXgn" href="#docusaurus_skipToContent_fallback">Skip to main content</a></div><div class="announcementBar_mb4j" style="background-color:#282826;color:#fff" role="banner"><div class="content_knG7 announcementBarContent_xLdY">
<a class="announcement-bar" href="https://registration.socio.events/e/pulsarvirtualsummiteurope2024" target="_blank">
<div class="announcement-bar__content">
<svg class="announcement-bar__icon">
<svg viewBox="0 0 33 32" fill="none" xmlns="http://www.w3.org/2000/svg">
<path d="M6.5 19.6001H16.1L15.3 29.2001L26.5 12.4H17.06L18.1 2.80005L6.5 19.6001Z" stroke="#F7F7F7" stroke-width="1.5" stroke-linejoin="round"/>
</svg>
</svg>
<span>
Get your free pass for Pulsar Virtual Summit Europe 2024 on May 14, 2024 🗓️
</span>
<svg class="announcement-bar__icon">
<svg viewBox="0 0 32 32" fill="none" xmlns="http://www.w3.org/2000/svg">
<rect width="20" height="20" transform="translate(6 6)" fill="white" fill-opacity="0.01"/>
<path d="M17.6667 10.1667L23.5 16.0001M23.5 16.0001L17.6667 21.8334M23.5 16.0001L8.5 16.0001" stroke="white" stroke-linecap="round" stroke-linejoin="round"/>
<rect x="0.5" y="0.5" width="31" height="31" rx="15.5" stroke="white"/>
</svg>
</svg>
</div>
</a>
</div></div><nav aria-label="Main" class="navbar navbar--fixed-top"><div class="navbar__inner"><div class="navbar__items"><button aria-label="Toggle navigation bar" aria-expanded="false" class="navbar__toggle clean-btn" type="button"><svg width="30" height="30" viewBox="0 0 30 30" aria-hidden="true"><path stroke="currentColor" stroke-linecap="round" stroke-miterlimit="10" stroke-width="2" d="M4 7h22M4 15h22M4 23h22"></path></svg></button><a class="navbar__brand" href="/"><div class="navbar__logo"><img src="/img/logo-black.svg" alt="Apache Pulsar logo" class="themedImage_ToTc themedImage--light_HNdA" height="25" width="127"><img src="/img/logo-black.svg" alt="Apache Pulsar logo" class="themedImage_ToTc themedImage--dark_i4oU" height="25" width="127"></div><b class="navbar__title text--truncate"></b></a><div class="navbar__item dropdown dropdown--hoverable"><a href="#" aria-haspopup="true" aria-expanded="false" role="button" class="navbar__link">Get Started</a><ul class="dropdown__menu"><li><a class="dropdown__link" href="/docs/3.2.x/concepts-overview/">Concepts</a></li><li><a class="dropdown__link" href="/docs/3.2.x/">Quickstart</a></li><li><a class="dropdown__link" href="/ecosystem/">Ecosystem</a></li></ul></div><a aria-current="page" class="navbar__item navbar__link navbar__link--active" href="/docs/3.0.x/">Docs</a><a class="navbar__item navbar__link" href="/features/">Features</a><a class="navbar__item navbar__link" href="/use-cases/">Use Cases</a><div class="navbar__item dropdown dropdown--hoverable"><a href="#" aria-haspopup="true" aria-expanded="false" role="button" class="navbar__link community-dropdown">Community</a><ul class="dropdown__menu"><li><a class="dropdown__link scroll-link scroll-welcome" id="scroll-welcome" href="/community/">Welcome</a></li><li><a class="dropdown__link scroll-link scroll-discussions" id="scroll-discussions" href="/community/#section-discussions">Discussions</a></li><li><a class="dropdown__link scroll-link" id="scroll-governance" href="/community/#section-governance">Governance</a></li><li><a class="dropdown__link scroll-link" id="scroll-community" href="/community/#section-community">Meet the Community</a></li><li><a class="dropdown__link scroll-link" id="scroll-contribute" href="/community/#section-contribute">Contribute</a></li><li><a class="dropdown__link" href="/contribute/">Contribution Guide</a></li><li><a href="https://github.com/apache/pulsar/wiki" target="_blank" rel="noopener noreferrer" class="dropdown__link">Wiki</a></li><li><a href="https://github.com/apache/pulsar/issues" target="_blank" rel="noopener noreferrer" class="dropdown__link">Issue Tracking</a></li></ul></div><div class="navbar__item dropdown dropdown--hoverable"><a href="#" aria-haspopup="true" aria-expanded="false" role="button" class="navbar__link">Learn</a><ul class="dropdown__menu"><li><a class="dropdown__link" href="/blog/">Blog</a></li><li><a class="dropdown__link" href="/books/">Books</a></li><li><a class="dropdown__link" href="/case-studies/">Case Studies</a></li><li><a class="dropdown__link" href="/articles/">Articles</a></li><li><a class="dropdown__link" href="/presentations/">Presentations</a></li><li><a class="dropdown__link" href="/events/">Events</a></li></ul></div></div><div class="navbar__items navbar__items--right"><a class="navbar__item navbar__link navbar_download_button" href="/download/">Download</a><div class="searchBox_ZlJk"><button type="button" class="DocSearch DocSearch-Button" aria-label="Search"><span class="DocSearch-Button-Container"><svg width="20" height="20" class="DocSearch-Search-Icon" viewBox="0 0 20 20" aria-hidden="true"><path d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z" stroke="currentColor" fill="none" fill-rule="evenodd" stroke-linecap="round" stroke-linejoin="round"></path></svg><span class="DocSearch-Button-Placeholder">Search</span></span><span class="DocSearch-Button-Keys"></span></button></div></div></div><div role="presentation" class="navbar-sidebar__backdrop"></div></nav><div id="docusaurus_skipToContent_fallback" class="main-wrapper mainWrapper_z2l0 docsWrapper_BCFX"><button aria-label="Scroll back to top" class="clean-btn theme-back-to-top-button backToTopButton_sjWU" type="button"></button><div class="docPage__5DB"><aside class="theme-doc-sidebar-container docSidebarContainer_b6E3"><div class="sidebarViewport_Xe31"><div class="sidebar_mhZE"><div class="sidebarVersionSwitch_EHpo">Version:<div class="navbar__item dropdown dropdown--hoverable"><a aria-current="page" class="navbar__link active" aria-haspopup="true" aria-expanded="false" role="button" href="/docs/3.0.x/">3.0.x</a><ul class="dropdown__menu"><li><a class="dropdown__link">Next</a></li><li><a class="dropdown__link">3.2.x</a></li><li><a class="dropdown__link">3.0.x LTS</a></li><li><a class="dropdown__link">Others</a></li></ul></div></div><nav aria-label="Docs sidebar" class="menu thin-scrollbar menu_SIkG menuWithAnnouncementBar_GW3s"><ul class="theme-doc-sidebar-menu menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-1 menu__list-item"><a class="menu__link" href="/docs/3.0.x/">About</a></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist" aria-expanded="false" href="/docs/3.0.x/getting-started-home/">Get Started</a><button aria-label="Toggle the collapsible sidebar category &#x27;Get Started&#x27;" type="button" class="clean-btn menu__caret"></button></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/3.0.x/concepts-overview/">Concepts and Architecture</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/3.0.x/schema-overview/">Pulsar Schema</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/3.0.x/functions-overview/">Pulsar Functions</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/3.0.x/io-overview/">Pulsar IO</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/3.0.x/sql-overview/">Pulsar SQL</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/3.0.x/tiered-storage-overview/">Tiered Storage</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/3.0.x/txn-why/">Transactions</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist" aria-expanded="false" href="/docs/3.0.x/install-deploy-upgrade-landing/">Deployment</a><button aria-label="Toggle the collapsible sidebar category &#x27;Deployment&#x27;" type="button" class="clean-btn menu__caret"></button></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/3.0.x/administration-zk-bk/">Administration</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/3.0.x/administration-stats/">Observability</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/3.0.x/security-overview/">Security</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/3.0.x/performance-pulsar-perf/">Performance</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret menu__link--active" aria-expanded="true" href="/docs/3.0.x/client-libraries/">Client Libraries</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/docs/3.0.x/client-libraries/">Overview</a></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-2 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" tabindex="0" href="/docs/3.0.x/client-libraries-java/">Get started</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-2 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret menu__link--active" aria-expanded="true" tabindex="0" href="/docs/3.0.x/client-libraries-clients/">Advanced use</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="/docs/3.0.x/client-libraries-clients/">Work with clients</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="/docs/3.0.x/client-libraries-producers/">Work with producer</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="/docs/3.0.x/client-libraries-consumers/">Work with consumer</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link menu__link--active" aria-current="page" tabindex="0" href="/docs/3.0.x/client-libraries-readers/">Work with reader</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="/docs/3.0.x/client-libraries-tableviews/">Work with TableView</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="/docs/3.0.x/client-libraries-schema/">Work with schema</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="/docs/3.0.x/client-libraries-cluster-level-failover/">Configure cluster-level failover</a></li></ul></li></ul></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/3.0.x/admin-api-overview/">Admin API</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/docs/3.0.x/adaptors-kafka/">Adaptors</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist" aria-expanded="false" href="/docs/3.0.x/how-to-landing/">Tutorials</a><button aria-label="Toggle the collapsible sidebar category &#x27;Tutorials&#x27;" type="button" class="clean-btn menu__caret"></button></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist" aria-expanded="false" href="/docs/3.0.x/developers-landing/">Development</a><button aria-label="Toggle the collapsible sidebar category &#x27;Development&#x27;" type="button" class="clean-btn menu__caret"></button></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist" aria-expanded="false" href="/docs/3.0.x/reference-landing/">Reference</a><button aria-label="Toggle the collapsible sidebar category &#x27;Reference&#x27;" type="button" class="clean-btn menu__caret"></button></div></li></ul></nav></div></div></aside><main class="docMainContainer_gTbr"><div class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_VOVn"><div class="docItemContainer_Djhp"><article><nav class="theme-doc-breadcrumbs breadcrumbsContainer_Z_bl" aria-label="Breadcrumbs"><ul class="breadcrumbs" itemscope="" itemtype="https://schema.org/BreadcrumbList"><li class="breadcrumbs__item"><a aria-label="Home page" class="breadcrumbs__link" href="/"><svg viewBox="0 0 24 24" class="breadcrumbHomeIcon_YNFT"><path d="M10 19v-5h4v5c0 .55.45 1 1 1h3c.55 0 1-.45 1-1v-7h1.7c.46 0 .68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill="currentColor"></path></svg></a></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">Client Libraries</span><meta itemprop="position" content="1"></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">Advanced use</span><meta itemprop="position" content="2"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">Work with reader</span><meta itemprop="position" content="3"></li></ul></nav><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><header><h1>Work with reader</h1></header><p>After setting up your clients, you can explore more to start working with <a href="/docs/3.0.x/concepts-clients/#reader-interface">readers</a>.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="receive-and-read-messages">Receive and read messages<a href="#receive-and-read-messages" class="hash-link" aria-label="Direct link to Receive and read messages" title="Direct link to Receive and read messages">​</a></h2><p>A reader is just a consumer without a cursor. This means that Pulsar does not keep track of your progress and there is no need to acknowledge messages.</p><p>Here&#x27;s an example that begins reading from the earliest available message on a topic.</p><div class="tabs-container tabList__CuJ"><ul role="tablist" aria-orientation="horizontal" class="tabs"><li role="tab" tabindex="0" aria-selected="true" class="tabs__item tabItem_LNqP tabs__item--active">Java</li><li role="tab" tabindex="-1" aria-selected="false" class="tabs__item tabItem_LNqP">C#</li></ul><div class="margin-top--md"><div role="tabpanel" class="tabItem_Ymn6"><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">import</span><span class="token plain"> </span><span class="token import namespace">org</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import namespace">apache</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import namespace">pulsar</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import namespace">client</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import namespace">api</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import class-name">Message</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">import</span><span class="token plain"> </span><span class="token import namespace">org</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import namespace">apache</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import namespace">pulsar</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import namespace">client</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import namespace">api</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import class-name">MessageId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">import</span><span class="token plain"> </span><span class="token import namespace">org</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import namespace">apache</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import namespace">pulsar</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import namespace">client</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import namespace">api</span><span class="token import namespace punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token import class-name">Reader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token comment" style="color:rgb(98, 114, 164)">// Create a reader on a topic and for a specific message (and onward)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token class-name">Reader</span><span class="token operator">&lt;</span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">byte</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token operator">&gt;</span><span class="token plain"> reader </span><span class="token operator">=</span><span class="token plain"> pulsarClient</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">newReader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token string" style="color:rgb(255, 121, 198)">&quot;reader-api-test&quot;</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">startMessageId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">MessageId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">earliest</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">create</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">while</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token boolean">true</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token class-name">Message</span><span class="token plain"> message </span><span class="token operator">=</span><span class="token plain"> reader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">readNext</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// Process the message</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></div><div role="tabpanel" class="tabItem_Ymn6" hidden=""><div class="language-csharp codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-csharp codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">await</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">foreach</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name keyword" style="color:rgb(189, 147, 249);font-style:italic">var</span><span class="token plain"> message </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">in</span><span class="token plain"> reader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Messages</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> Console</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">WriteLine</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token string" style="color:rgb(255, 121, 198)">&quot;Received: &quot;</span><span class="token plain"> </span><span class="token operator">+</span><span class="token plain"> Encoding</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">UTF8</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">GetString</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">message</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">Data</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">ToArray</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></div></div></div><h3 class="anchor anchorWithStickyNavbar_LWe7" id="read-next-message">Read <code>next</code> message<a href="#read-next-message" class="hash-link" aria-label="Direct link to read-next-message" title="Direct link to read-next-message">​</a></h3><p>To create a reader that reads from the latest available message:</p><div class="tabs-container tabList__CuJ"><ul role="tablist" aria-orientation="horizontal" class="tabs"><li role="tab" tabindex="0" aria-selected="true" class="tabs__item tabItem_LNqP tabs__item--active">Java</li><li role="tab" tabindex="-1" aria-selected="false" class="tabs__item tabItem_LNqP">Go</li></ul><div class="margin-top--md"><div role="tabpanel" class="tabItem_Ymn6"><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token class-name">Reader</span><span class="token operator">&lt;</span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">byte</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token operator">&gt;</span><span class="token plain"> reader </span><span class="token operator">=</span><span class="token plain"> pulsarClient</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">newReader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">startMessageId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">MessageId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">latest</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">create</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></div><div role="tabpanel" class="tabItem_Ymn6" hidden=""><div class="language-go codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-go codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">import</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">&quot;context&quot;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">&quot;fmt&quot;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">&quot;log&quot;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">&quot;github.com/apache/pulsar-client-go/pulsar&quot;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">func</span><span class="token plain"> </span><span class="token function" style="color:rgb(80, 250, 123)">main</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> client</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> err </span><span class="token operator">:=</span><span class="token plain"> pulsar</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">NewClient</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">pulsar</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">ClientOptions</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain">URL</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">&quot;pulsar://localhost:6650&quot;</span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">if</span><span class="token plain"> err </span><span class="token operator">!=</span><span class="token plain"> </span><span class="token boolean">nil</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> log</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Fatal</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">err</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">defer</span><span class="token plain"> client</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Close</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> reader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> err </span><span class="token operator">:=</span><span class="token plain"> client</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">CreateReader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">pulsar</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">ReaderOptions</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> Topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">&quot;topic-1&quot;</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> StartMessageID</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> pulsar</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">EarliestMessageID</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">if</span><span class="token plain"> err </span><span class="token operator">!=</span><span class="token plain"> </span><span class="token boolean">nil</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> log</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Fatal</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">err</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">defer</span><span class="token plain"> reader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Close</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">for</span><span class="token plain"> reader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">HasNext</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> msg</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> err </span><span class="token operator">:=</span><span class="token plain"> reader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Next</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">context</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Background</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">if</span><span class="token plain"> err </span><span class="token operator">!=</span><span class="token plain"> </span><span class="token boolean">nil</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> log</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Fatal</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">err</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> fmt</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Printf</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token string" style="color:rgb(255, 121, 198)">&quot;Received message msgId: %#v -- content: &#x27;%s&#x27;\n&quot;</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> msg</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">ID</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token function" style="color:rgb(80, 250, 123)">string</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">msg</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Payload</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>In the example above, the reader begins reading from the earliest available message (specified by <code>pulsar.EarliestMessage</code>). The reader can also begin reading from the latest message (<code>pulsar.LatestMessage</code>) or some other message ID specified by bytes using the <code>DeserializeMessageID</code> function, which takes a byte array and returns a <code>MessageID</code> object. Here&#x27;s an example:</p><div class="language-go codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-go codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token plain">lastSavedId </span><span class="token operator">:=</span><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// Read last saved message id from external store as byte[]</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain">reader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> err </span><span class="token operator">:=</span><span class="token plain"> client</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">CreateReader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">pulsar</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">ReaderOptions</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> Topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">&quot;my-golang-topic&quot;</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> StartMessageID</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> pulsar</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">DeserializeMessageID</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">lastSavedId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></div></div></div><h3 class="anchor anchorWithStickyNavbar_LWe7" id="read-specific-messages">Read specific messages<a href="#read-specific-messages" class="hash-link" aria-label="Direct link to Read specific messages" title="Direct link to Read specific messages">​</a></h3><p>To create a reader that reads from some message between the earliest and the latest:</p><div class="tabs-container tabList__CuJ"><ul role="tablist" aria-orientation="horizontal" class="tabs"><li role="tab" tabindex="0" aria-selected="true" class="tabs__item tabItem_LNqP tabs__item--active">Java</li><li role="tab" tabindex="-1" aria-selected="false" class="tabs__item tabItem_LNqP">Go</li></ul><div class="margin-top--md"><div role="tabpanel" class="tabItem_Ymn6"><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">byte</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token plain"> msgIdBytes </span><span class="token operator">=</span><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// Some byte array</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token class-name">MessageId</span><span class="token plain"> id </span><span class="token operator">=</span><span class="token plain"> </span><span class="token class-name">MessageId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">fromByteArray</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">msgIdBytes</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token class-name">Reader</span><span class="token operator">&lt;</span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">byte</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token operator">&gt;</span><span class="token plain"> reader </span><span class="token operator">=</span><span class="token plain"> pulsarClient</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">newReader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">startMessageId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">id</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">create</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></div><div role="tabpanel" class="tabItem_Ymn6" hidden=""><div class="language-go codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-go codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token plain">client</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> err </span><span class="token operator">:=</span><span class="token plain"> pulsar</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">NewClient</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">pulsar</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">ClientOptions</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> URL</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">&quot;pulsar://localhost:6650&quot;</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">if</span><span class="token plain"> err </span><span class="token operator">!=</span><span class="token plain"> </span><span class="token boolean">nil</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> log</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Fatal</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">err</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">defer</span><span class="token plain"> client</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Close</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain">topic </span><span class="token operator">:=</span><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">&quot;topic-1&quot;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain">ctx </span><span class="token operator">:=</span><span class="token plain"> context</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Background</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token comment" style="color:rgb(98, 114, 164)">// create producer</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain">producer</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> err </span><span class="token operator">:=</span><span class="token plain"> client</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">CreateProducer</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">pulsar</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">ProducerOptions</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> Topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> DisableBatching</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> </span><span class="token boolean">true</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">if</span><span class="token plain"> err </span><span class="token operator">!=</span><span class="token plain"> </span><span class="token boolean">nil</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> log</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Fatal</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">err</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">defer</span><span class="token plain"> producer</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Close</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token comment" style="color:rgb(98, 114, 164)">// send 10 messages</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain">msgIDs </span><span class="token operator">:=</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token number">10</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token plain">pulsar</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">MessageID</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">for</span><span class="token plain"> i </span><span class="token operator">:=</span><span class="token plain"> </span><span class="token number">0</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"> i </span><span class="token operator">&lt;</span><span class="token plain"> </span><span class="token number">10</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"> i</span><span class="token operator">++</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> msgID</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token boolean">_</span><span class="token plain"> </span><span class="token operator">:=</span><span class="token plain"> producer</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Send</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">ctx</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token operator">&amp;</span><span class="token plain">pulsar</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">ProducerMessage</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> Payload</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token function" style="color:rgb(80, 250, 123)">byte</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">fmt</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Sprintf</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token string" style="color:rgb(255, 121, 198)">&quot;hello-%d&quot;</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> i</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> msgIDs</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token plain">i</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token plain"> </span><span class="token operator">=</span><span class="token plain"> msgID</span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token comment" style="color:rgb(98, 114, 164)">// create reader on 5th message (not included)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain">reader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> err </span><span class="token operator">:=</span><span class="token plain"> client</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">CreateReader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">pulsar</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">ReaderOptions</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> Topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> StartMessageID</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> msgIDs</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token number">4</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> StartMessageIDInclusive</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> </span><span class="token boolean">false</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">if</span><span class="token plain"> err </span><span class="token operator">!=</span><span class="token plain"> </span><span class="token boolean">nil</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> log</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Fatal</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">err</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">defer</span><span class="token plain"> reader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Close</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token comment" style="color:rgb(98, 114, 164)">// receive the remaining 5 messages</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">for</span><span class="token plain"> i </span><span class="token operator">:=</span><span class="token plain"> </span><span class="token number">5</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"> i </span><span class="token operator">&lt;</span><span class="token plain"> </span><span class="token number">10</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"> i</span><span class="token operator">++</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> msg</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> err </span><span class="token operator">:=</span><span class="token plain"> reader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Next</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">context</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Background</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">if</span><span class="token plain"> err </span><span class="token operator">!=</span><span class="token plain"> </span><span class="token boolean">nil</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> log</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Fatal</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">err</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> fmt</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Printf</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token string" style="color:rgb(255, 121, 198)">&quot;Read %d-th msg: %s\n&quot;</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> i</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token function" style="color:rgb(80, 250, 123)">string</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">msg</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Payload</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token comment" style="color:rgb(98, 114, 164)">// create reader on 5th message (included)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain">readerInclusive</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> err </span><span class="token operator">:=</span><span class="token plain"> client</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">CreateReader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">pulsar</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">ReaderOptions</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> Topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> StartMessageID</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> msgIDs</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token number">4</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> StartMessageIDInclusive</span><span class="token punctuation" style="color:rgb(248, 248, 242)">:</span><span class="token plain"> </span><span class="token boolean">true</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">if</span><span class="token plain"> err </span><span class="token operator">!=</span><span class="token plain"> </span><span class="token boolean">nil</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> log</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Fatal</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">err</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">defer</span><span class="token plain"> readerInclusive</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">Close</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></div></div></div><h2 class="anchor anchorWithStickyNavbar_LWe7" id="configure-chunking">Configure chunking<a href="#configure-chunking" class="hash-link" aria-label="Direct link to Configure chunking" title="Direct link to Configure chunking">​</a></h2><p>Configuring chunking for readers is similar to that for consumers. See <a href="#configure-chunking">configure chunking for consumers</a> for more information.</p><p>The following is an example of how to configure message chunking for a reader.</p><div class="tabs-container tabList__CuJ"><ul role="tablist" aria-orientation="horizontal" class="tabs"><li role="tab" tabindex="0" aria-selected="true" class="tabs__item tabItem_LNqP tabs__item--active">Java</li></ul><div class="margin-top--md"><div role="tabpanel" class="tabItem_Ymn6"><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token class-name">Reader</span><span class="token operator">&lt;</span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">byte</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token operator">&gt;</span><span class="token plain"> reader </span><span class="token operator">=</span><span class="token plain"> pulsarClient</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">newReader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">topicName</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">startMessageId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">MessageId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">earliest</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">maxPendingChunkedMessage</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token number">12</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">autoAckOldestChunkedMessageOnQueueFull</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token boolean">true</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">expireTimeOfIncompleteChunkedMessage</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token number">12</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token class-name">TimeUnit</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token constant" style="color:rgb(189, 147, 249)">MILLISECONDS</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">create</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></div></div></div><h2 class="anchor anchorWithStickyNavbar_LWe7" id="intercept-messages">Intercept messages<a href="#intercept-messages" class="hash-link" aria-label="Direct link to Intercept messages" title="Direct link to Intercept messages">​</a></h2><p>Pulsar reader interceptor intercepts and possibly mutates messages with user-defined processing before <a href="/docs/3.0.x/concepts-clients/#reader-interface">Pulsar reader</a> reads them. With reader interceptors, you can apply unified messaging processes before messages can be read, such as modifying messages, adding properties, collecting statistics and etc, without creating similar mechanisms respectively.</p><p><img loading="lazy" alt="Reader interceptor" src="/assets/images/reader-interceptor-29f6b3d84db93608da79169bf9901555.svg" width="1048" height="237" class="img_ev3q"></p><p>Pulsar reader interceptor works on top of Pulsar consumer interceptor. The plugin interface <code>ReaderInterceptor</code> can be treated as a subset of <code>ConsumerInterceptor</code> and it has two main events.</p><ul><li><code>beforeRead</code> is triggered before readers read messages. You can modify messages within this event.</li><li><code>onPartitionsChange</code> is triggered when changes on partitions have been detected.</li></ul><p>To perceive triggered events and perform customized processing, you can add <code>ReaderInterceptor</code> when creating a <code>Reader</code> as follows.</p><div class="tabs-container tabList__CuJ"><ul role="tablist" aria-orientation="horizontal" class="tabs"><li role="tab" tabindex="0" aria-selected="true" class="tabs__item tabItem_LNqP tabs__item--active">Java</li></ul><div class="margin-top--md"><div role="tabpanel" class="tabItem_Ymn6"><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token class-name">PulsarClient</span><span class="token plain"> pulsarClient </span><span class="token operator">=</span><span class="token plain"> </span><span class="token class-name">PulsarClient</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">builder</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">serviceUrl</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token string" style="color:rgb(255, 121, 198)">&quot;pulsar://localhost:6650&quot;</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">build</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token class-name">Reader</span><span class="token operator">&lt;</span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">byte</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token operator">&gt;</span><span class="token plain"> reader </span><span class="token operator">=</span><span class="token plain"> pulsarClient</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">newReader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token string" style="color:rgb(255, 121, 198)">&quot;t1&quot;</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">autoUpdatePartitionsInterval</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token number">5</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token class-name">TimeUnit</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token constant" style="color:rgb(189, 147, 249)">SECONDS</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">intercept</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">new</span><span class="token plain"> </span><span class="token class-name">ReaderInterceptor</span><span class="token operator">&lt;</span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">byte</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token operator">&gt;</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token annotation punctuation" style="color:rgb(248, 248, 242)">@Override</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">public</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">void</span><span class="token plain"> </span><span class="token function" style="color:rgb(80, 250, 123)">close</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token annotation punctuation" style="color:rgb(248, 248, 242)">@Override</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">public</span><span class="token plain"> </span><span class="token class-name">Message</span><span class="token operator">&lt;</span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">byte</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token operator">&gt;</span><span class="token plain"> </span><span class="token function" style="color:rgb(80, 250, 123)">beforeRead</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">Reader</span><span class="token operator">&lt;</span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">byte</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token operator">&gt;</span><span class="token plain"> reader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token class-name">Message</span><span class="token operator">&lt;</span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">byte</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token operator">&gt;</span><span class="token plain"> message</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// user-defined processing logic</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">return</span><span class="token plain"> message</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token annotation punctuation" style="color:rgb(248, 248, 242)">@Override</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">public</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">void</span><span class="token plain"> </span><span class="token function" style="color:rgb(80, 250, 123)">onPartitionsChange</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">String</span><span class="token plain"> topicName</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">int</span><span class="token plain"> partitions</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// user-defined processing logic</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">startMessageId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">MessageId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">earliest</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">create</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></div></div></div><h2 class="anchor anchorWithStickyNavbar_LWe7" id="sticky-key-range-reader">Sticky key range reader<a href="#sticky-key-range-reader" class="hash-link" aria-label="Direct link to Sticky key range reader" title="Direct link to Sticky key range reader">​</a></h2><p>In a sticky key range reader, broker only dispatches messages which hash of the message key contains by the specified key hash range. Multiple key hash ranges can be specified on a reader.</p><p>The following is an example to create a sticky key range reader.</p><div class="tabs-container tabList__CuJ"><ul role="tablist" aria-orientation="horizontal" class="tabs"><li role="tab" tabindex="0" aria-selected="true" class="tabs__item tabItem_LNqP tabs__item--active">Java</li></ul><div class="margin-top--md"><div role="tabpanel" class="tabItem_Ymn6"><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token plain">pulsarClient</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">newReader</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">startMessageId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">MessageId</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">earliest</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">keyHashRange</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">Range</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">of</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token number">0</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token number">10000</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token class-name">Range</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">of</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token number">20001</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token number">30000</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">create</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div></div></div></div><p>The total hash range size is 65536, so the max end of the range should be less than or equal to 65535.</p></div><footer class="theme-doc-footer docusaurus-mt-lg"><div class="theme-doc-footer-edit-meta-row row"><div class="col"><a href="https://github.com/apache/pulsar-site/edit/main/versioned_docs/version-3.0.x/client-libraries-readers.md" target="_blank" rel="noreferrer noopener" class="theme-edit-this-page"><svg fill="currentColor" height="20" width="20" viewBox="0 0 40 40" class="iconEdit_Z9Sw" aria-hidden="true"><g><path d="m34.5 11.7l-3 3.1-6.3-6.3 3.1-3q0.5-0.5 1.2-0.5t1.1 0.5l3.9 3.9q0.5 0.4 0.5 1.1t-0.5 1.2z m-29.5 17.1l18.4-18.5 6.3 6.3-18.4 18.4h-6.3v-6.2z"></path></g></svg>Edit this page</a></div><div class="col lastUpdated_vwxv"></div></div></footer></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages navigation"><a class="pagination-nav__link pagination-nav__link--prev" href="/docs/3.0.x/client-libraries-consumers/"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">Work with consumer</div></a><a class="pagination-nav__link pagination-nav__link--next" href="/docs/3.0.x/client-libraries-tableviews/"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">Work with TableView</div></a></nav></div></div><div class="col col--3"><div class="tableOfContents_jeP5 thin-scrollbar theme-doc-toc-desktop"><div class="border"><div style="color:var(--ifm-toc-link-color)">Was this helpful?</div><div style="border-width:1px;padding:3px;display:flex"><div style="justify-content:center;display:flex;border-radius:99999px;width:2.5rem;height:2.5rem;cursor:pointer;background:;color:"><svg style="width:initial;height:initial" width="12" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg"><path fill-rule="evenodd" clip-rule="evenodd" d="M10.086 1.594A1 1 0 0 1 11 1a4 4 0 0 1 4 4v3h4.655a3 3 0 0 1 2.994 3.45l-1.38 9A3.002 3.002 0 0 1 18.275 23H4a3 3 0 0 1-3-3v-7a3 3 0 0 1 3-3h2.35l3.736-8.406ZM8 11.212l3.608-8.117A2 2 0 0 1 13 5v4a1 1 0 0 0 1 1h5.671a1 1 0 0 1 1 1.15l-1.38 9a1 1 0 0 1-1 .85H8v-9.788ZM6 21v-9H4a1 1 0 0 0-1 1v7a1 1 0 0 0 1 1h2Z" fill="currentColor"></path></svg></div><div style="justify-content:center;display:flex;border-radius:99999px;width:2.5rem;height:2.5rem;cursor:pointer;background:;color:"><svg style="width:initial;height:initial" width="12" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg"><path fill-rule="evenodd" clip-rule="evenodd" d="M20.563 3.316A1.31 1.31 0 0 0 19.687 3h-1.688v9h1.688a1.31 1.31 0 0 0 1.312-1.077V4.077a1.31 1.31 0 0 0-.436-.761ZM16 12.788l-3.608 8.117A1.999 1.999 0 0 1 11 19v-4a1 1 0 0 0-1-1H4.328a1.002 1.002 0 0 1-1-1.15l1.38-9a1 1 0 0 1 1-.85h10.291v9.788ZM19.661 1a3.31 3.31 0 0 1 3.329 2.866c.006.044.01.09.01.134v7c0 .045-.004.09-.01.134A3.31 3.31 0 0 1 19.661 14h-2.012l-3.736 8.406a1 1 0 0 1-.914.594 4 4 0 0 1-4-4v-3H4.344a3 3 0 0 1-2.994-3.45l1.38-9A3.002 3.002 0 0 1 5.724 1h13.937Z" fill="currentColor"></path></svg></div></div><div class="Actions_uugI"><a target="_blank" class="Action_iBHd" href="https://github.com/apache/pulsar/issues/new?assignees=&amp;labels=doc-required&amp;projects=&amp;template=doc.yml&amp;title=%5BDoc%5D+">💡 Suggest changes</a><a target="_blank" class="Action_iBHd" href="https://github.com/apache/pulsar/discussions/new?category=q-a">🛟 Get support</a></div></div><ul class="table-of-contents table-of-contents__left-border"><li><a href="#receive-and-read-messages" class="table-of-contents__link toc-highlight">Receive and read messages</a><ul><li><a href="#read-next-message" class="table-of-contents__link toc-highlight">Read <code>next</code> message</a></li><li><a href="#read-specific-messages" class="table-of-contents__link toc-highlight">Read specific messages</a></li></ul></li><li><a href="#configure-chunking" class="table-of-contents__link toc-highlight">Configure chunking</a></li><li><a href="#intercept-messages" class="table-of-contents__link toc-highlight">Intercept messages</a></li><li><a href="#sticky-key-range-reader" class="table-of-contents__link toc-highlight">Sticky key range reader</a></li></ul></div></div></div></div></main></div></div><footer class="footer"><div class="container container-fluid"><div class="row footer__links"><div class="col footer__col"><div class="footer__title"></div><ul class="footer__items clean-list"><li class="footer__item"><a href="https://www.apache.org/" target="_blank" rel="noopener noreferrer" class="footer__link-item">Foundation<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li><li class="footer__item"><a href="https://www.apache.org/events/current-event.html" target="_blank" rel="noopener noreferrer" class="footer__link-item">Events<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li></ul></div><div class="col footer__col"><div class="footer__title"></div><ul class="footer__items clean-list"><li class="footer__item"><a href="https://www.apache.org/licenses/" target="_blank" rel="noopener noreferrer" class="footer__link-item">License<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li><li class="footer__item"><a href="https://www.apache.org/foundation/thanks" target="_blank" rel="noopener noreferrer" class="footer__link-item">Thanks<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li><li class="footer__item"><a href="https://www.apache.org/foundation/sponsorship" target="_blank" rel="noopener noreferrer" class="footer__link-item">Sponsorship<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li></ul></div><div class="col footer__col"><div class="footer__title"></div><ul class="footer__items clean-list"><li class="footer__item"><a class="footer__link-item" href="/security/">Security</a></li><li class="footer__item"><a href="https://www.apache.org/foundation/policies/privacy.html" target="_blank" rel="noopener noreferrer" class="footer__link-item">Privacy<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li><li class="footer__item"><a class="footer__link-item" href="/contact/">Contact</a></li></ul></div><div class="col footer__col"><div class="footer__title"></div><ul class="footer__items clean-list"><li class="footer__item">
<div class="social-icons">
<a target="_blank" href="https://communityinviter.com/apps/apache-pulsar/apache-pulsar" aria-label="Join the Apache Pulsar Slack workspace">
<img alt="Slack logo" src="/img/slack-white.svg" width="26">
</a>
<a target="_blank" href="https://github.com/apache/pulsar/" aria-label="View the Apache Pulsar project on GitHub">
<img alt="GitHub logo" src="/img/github-white.svg" width="26">
</a>
</div>
</li></ul></div></div><div class="footer__bottom text--center"><div class="margin-bottom--sm"><a class="footerLogoLink_BH7S" href="/"><img src="/img/pulsar-white.svg" alt="Pulsar Logo" class="themedImage_ToTc themedImage--light_HNdA footer__logo"><img src="/img/pulsar-white.svg" alt="Pulsar Logo" class="themedImage_ToTc themedImage--dark_i4oU footer__logo"></a></div><div class="footer__copyright">
<div>
<img class="footer-apache-logo" src="/img/feather-logo-white.svg" alt="" width="20">
The Apache Software Foundation
</div>
<p>Apache Pulsar is available under the Apache License, version 2.0. Apache Pulsar is an open-source, distributed messaging and streaming platform built for the cloud.</p>
<p>Copyright © 2024 The Apache Software Foundation. All Rights Reserved. Apache, Pulsar, Apache Pulsar, and the Apache feather logo are trademarks or registered trademarks of The Apache Software Foundation.</p>
</div></div></div></footer></div>
<script src="/assets/js/runtime~main.f1ab6cb0.js"></script>
<script src="/assets/js/main.9801eec2.js"></script>
</body>
</html>