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<!DOCTYPE html><html lang="en"><head><meta charSet="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>Window Functions Context · Apache Pulsar</title><meta name="viewport" content="width=device-width, initial-scale=1.0"/><meta name="generator" content="Docusaurus"/><meta name="description" content="Java SDK provides access to a **window context object** that can be used by a window function. This context object provides a wide variety of information and functionality for Pulsar window functions as below."/><meta name="docsearch:version" content="2.4.2"/><meta name="docsearch:language" content="en"/><meta property="og:title" content="Window Functions Context · Apache Pulsar"/><meta property="og:type" content="website"/><meta property="og:url" content="https://pulsar.apache.org/"/><meta property="og:description" content="Java SDK provides access to a **window context object** that can be used by a window function. This context object provides a wide variety of information and functionality for Pulsar window functions as below."/><meta name="twitter:card" content="summary"/><meta name="twitter:image" content="https://pulsar.apache.org/img/pulsar.svg"/><link rel="shortcut icon" href="/img/pulsar.ico"/><link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/atom-one-dark.min.css"/><link rel="alternate" type="application/atom+xml" href="https://pulsar.apache.org/blog/atom.xml" title="Apache Pulsar Blog ATOM Feed"/><link rel="alternate" type="application/rss+xml" href="https://pulsar.apache.org/blog/feed.xml" title="Apache Pulsar Blog RSS Feed"/><link rel="stylesheet" href="/css/code-blocks-buttons.css"/><script type="text/javascript" src="https://buttons.github.io/buttons.js"></script><script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/clipboard.js/2.0.0/clipboard.min.js"></script><script type="text/javascript" src="/js/custom.js"></script><script src="/js/scrollSpy.js"></script><link rel="stylesheet" href="/css/main.css"/><script src="/js/codetabs.js"></script></head><body class="sideNavVisible separateOnPageNav"><div class="fixedHeaderContainer"><div class="headerWrapper wrapper"><header><a href="/en"><img class="logo" src="/img/pulsar.svg" alt="Apache Pulsar"/></a><a href="/en/versions"><h3>2.4.2</h3></a><div class="navigationWrapper navigationSlider"><nav class="slidingNav"><ul class="nav-site nav-site-internal"><li class="siteNavGroupActive"><a href="/docs/en/2.4.2/getting-started-standalone" target="_self">Docs</a></li><li class=""><a href="/en/download" target="_self">Download</a></li><li class="siteNavGroupActive"><a href="/docs/en/2.4.2/client-libraries" target="_self">Clients</a></li><li class=""><a href="#restapis" target="_self">REST APIs</a></li><li class=""><a href="#cli" target="_self">Cli</a></li><li class=""><a href="/blog/" target="_self">Blog</a></li><li class=""><a href="#community" target="_self">Community</a></li><li class=""><a href="#apache" target="_self">Apache</a></li><li class=""><a href="https://pulsar-next.staged.apache.org/" target="_self">New Website (Beta)</a></li><span><li><a id="languages-menu" href="#"><img class="languages-icon" src="/img/language.svg" alt="Languages icon"/>English</a><div id="languages-dropdown" class="hide"><ul id="languages-dropdown-items"><li><a href="/docs/ja/2.4.2/window-functions-context">日本語</a></li><li><a href="/docs/fr/2.4.2/window-functions-context">Français</a></li><li><a href="/docs/ko/2.4.2/window-functions-context">한국어</a></li><li><a href="/docs/zh-CN/2.4.2/window-functions-context">中文</a></li><li><a href="/docs/zh-TW/2.4.2/window-functions-context">繁體中文</a></li><li><a href="https://crowdin.com/project/apache-pulsar" target="_blank" rel="noreferrer noopener">Help Translate</a></li></ul></div></li><script>
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Metrics</a></li></ul></div></div></section></div><script>
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</script></nav></div><div class="container mainContainer docsContainer"><div class="wrapper"><div class="post"><header class="postHeader"><a class="edit-page-link button" href="https://github.com/apache/pulsar/edit/master/site2/docs/window-functions-context.md" target="_blank" rel="noreferrer noopener">Edit</a><h1 id="__docusaurus" class="postHeaderTitle">Window Functions Context</h1></header><article><div><span><p>Java SDK provides access to a <strong>window context object</strong> that can be used by a window function. This context object provides a wide variety of information and functionality for Pulsar window functions as below.</p>
<ul>
<li><p><a href="#spec">Spec</a></p>
<ul>
<li>Names of all input topics and the output topic associated with the function.</li>
<li>Tenant and namespace associated with the function.</li>
<li>Pulsar window function name, ID, and version.</li>
<li>ID of the Pulsar function instance running the window function.</li>
<li>Number of instances that invoke the window function.</li>
<li>Built-in type or custom class name of the output schema.</li>
</ul></li>
<li><p><a href="#logger">Logger</a></p>
<ul>
<li>Logger object used by the window function, which can be used to create window function log messages.</li>
</ul></li>
<li><p><a href="#user-config">User config</a></p>
<ul>
<li>Access to arbitrary user configuration values.</li>
</ul></li>
<li><p><a href="#routing">Routing</a></p>
<ul>
<li>Routing is supported in Pulsar window functions. Pulsar window functions send messages to arbitrary topics as per the <code>publish</code> interface.</li>
</ul></li>
<li><p><a href="#metrics">Metrics</a></p>
<ul>
<li>Interface for recording metrics.</li>
</ul></li>
<li><p><a href="#state-storage">State storage</a></p>
<ul>
<li>Interface for storing and retrieving state in <a href="#state-storage">state storage</a>.</li>
</ul></li>
</ul>
<h2><a class="anchor" aria-hidden="true" id="spec"></a><a href="#spec" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Spec</h2>
<p>Spec contains the basic information of a function.</p>
<h3><a class="anchor" aria-hidden="true" id="get-input-topics"></a><a href="#get-input-topics" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Get input topics</h3>
<p>The <code>getInputTopics</code> method gets the <strong>name list</strong> of all input topics.</p>
<p>This example demonstrates how to get the name list of all input topics in a Java window function.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">GetInputTopicsWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; inputs, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
Collection&lt;String&gt; inputTopics = context.getInputTopics();
System.out.println(inputTopics);
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="get-output-topic"></a><a href="#get-output-topic" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Get output topic</h3>
<p>The <code>getOutputTopic</code> method gets the <strong>name of a topic</strong> to which the message is sent.</p>
<p>This example demonstrates how to get the name of an output topic in a Java window function.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">GetOutputTopicWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; inputs, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
String outputTopic = context.getOutputTopic();
System.out.println(outputTopic);
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="get-tenant"></a><a href="#get-tenant" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Get tenant</h3>
<p>The <code>getTenant</code> method gets the tenant name associated with the window function.</p>
<p>This example demonstrates how to get the tenant name in a Java window function.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">GetTenantWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; inputs, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
String tenant = context.getTenant();
System.out.println(tenant);
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="get-namespace"></a><a href="#get-namespace" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Get namespace</h3>
<p>The <code>getNamespace</code> method gets the namespace associated with the window function.</p>
<p>This example demonstrates how to get the namespace in a Java window function.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">GetNamespaceWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; inputs, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
String ns = context.getNamespace();
System.out.println(ns);
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="get-function-name"></a><a href="#get-function-name" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Get function name</h3>
<p>The <code>getFunctionName</code> method gets the window function name.</p>
<p>This example demonstrates how to get the function name in a Java window function.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">GetNameOfWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; inputs, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
String functionName = context.getFunctionName();
System.out.println(functionName);
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="get-function-id"></a><a href="#get-function-id" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Get function ID</h3>
<p>The <code>getFunctionId</code> method gets the window function ID.</p>
<p>This example demonstrates how to get the function ID in a Java window function.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">GetFunctionIDWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; inputs, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
String functionID = context.getFunctionId();
System.out.println(functionID);
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="get-function-version"></a><a href="#get-function-version" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Get function version</h3>
<p>The <code>getFunctionVersion</code> method gets the window function version.</p>
<p>This example demonstrates how to get the function version of a Java window function.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">GetVersionOfWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; inputs, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
String functionVersion = context.getFunctionVersion();
System.out.println(functionVersion);
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="get-instance-id"></a><a href="#get-instance-id" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Get instance ID</h3>
<p>The <code>getInstanceId</code> method gets the instance ID of a window function.</p>
<p>This example demonstrates how to get the instance ID in a Java window function.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">GetInstanceIDWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; inputs, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
<span class="hljs-keyword">int</span> instanceId = context.getInstanceId();
System.out.println(instanceId);
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="get-num-instances"></a><a href="#get-num-instances" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Get num instances</h3>
<p>The <code>getNumInstances</code> method gets the number of instances that invoke the window function.</p>
<p>This example demonstrates how to get the number of instances in a Java window function.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">GetNumInstancesWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; inputs, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
<span class="hljs-keyword">int</span> numInstances = context.getNumInstances();
System.out.println(numInstances);
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="get-output-schema-type"></a><a href="#get-output-schema-type" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Get output schema type</h3>
<p>The <code>getOutputSchemaType</code> method gets the built-in type or custom class name of the output schema.</p>
<p>This example demonstrates how to get the output schema type of a Java window function.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">GetOutputSchemaTypeWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; inputs, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
String schemaType = context.getOutputSchemaType();
System.out.println(schemaType);
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="logger"></a><a href="#logger" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Logger</h2>
<p>Pulsar window functions using Java SDK has access to an <a href="https://www.slf4j.org/">SLF4j</a> <a href="https://www.slf4j.org/api/org/apache/log4j/Logger.html"><code>Logger</code></a> object that can be used to produce logs at the chosen log level.</p>
<p>This example logs either a <code>WARNING</code>-level or <code>INFO</code>-level log based on whether the incoming string contains the word <code>danger</code> or not in a Java function.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">import</span> java.util.Collection;
<span class="hljs-keyword">import</span> org.apache.pulsar.functions.api.Record;
<span class="hljs-keyword">import</span> org.apache.pulsar.functions.api.WindowContext;
<span class="hljs-keyword">import</span> org.apache.pulsar.functions.api.WindowFunction;
<span class="hljs-keyword">import</span> org.slf4j.Logger;
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">LoggingWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; inputs, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
Logger log = context.getLogger();
<span class="hljs-keyword">for</span> (Record&lt;String&gt; record : inputs) {
log.info(record + <span class="hljs-string">"-window-log"</span>);
}
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<p>If you need your function to produce logs, specify a log topic when creating or running the function.</p>
<pre><code class="hljs css language-bash">bin/pulsar-admin <span class="hljs-built_in">functions</span> create \
--jar my-functions.jar \
--classname my.package.LoggingFunction \
--<span class="hljs-built_in">log</span>-topic persistent://public/default/logging-function-logs \
<span class="hljs-comment"># Other function configs</span>
</code></pre>
<p>You can access all logs produced by <code>LoggingFunction</code> via the <code>persistent://public/default/logging-function-logs</code> topic.</p>
<h2><a class="anchor" aria-hidden="true" id="metrics"></a><a href="#metrics" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Metrics</h2>
<p>Pulsar window functions can publish arbitrary metrics to the metrics interface which can be queried.</p>
<blockquote>
<p><strong>Note</strong></p>
<p>If a Pulsar window function uses the language-native interface for Java, that function is not able to publish metrics and stats to Pulsar.</p>
</blockquote>
<p>You can record metrics using the context object on a per-key basis.</p>
<p>This example sets a metric for the <code>process-count</code> key and a different metric for the <code>elevens-count</code> key every time the function processes a message in a Java function.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">import</span> java.util.Collection;
<span class="hljs-keyword">import</span> org.apache.pulsar.functions.api.Record;
<span class="hljs-keyword">import</span> org.apache.pulsar.functions.api.WindowContext;
<span class="hljs-keyword">import</span> org.apache.pulsar.functions.api.WindowFunction;
<span class="hljs-comment">/**
* Example function that wants to keep track of
* the event time of each message sent.
*/</span>
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">UserMetricWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; inputs, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
<span class="hljs-keyword">for</span> (Record&lt;String&gt; record : inputs) {
<span class="hljs-keyword">if</span> (record.getEventTime().isPresent()) {
context.recordMetric(<span class="hljs-string">"MessageEventTime"</span>, record.getEventTime().get().doubleValue());
}
}
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="user-config"></a><a href="#user-config" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>User config</h2>
<p>When you run or update Pulsar Functions that are created using SDK, you can pass arbitrary key/value pairs to them with the <code>--user-config</code> flag. Key/value pairs <strong>must</strong> be specified as JSON.</p>
<p>This example passes a user configured key/value to a function.</p>
<pre><code class="hljs css language-bash">bin/pulsar-admin <span class="hljs-built_in">functions</span> create \
--name word-filter \
--user-config <span class="hljs-string">'{"forbidden-word":"rosebud"}'</span> \
<span class="hljs-comment"># Other function configs</span>
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="api"></a><a href="#api" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>API</h3>
<p>You can use the following APIs to get user-defined information for window functions.</p>
<h4><a class="anchor" aria-hidden="true" id="getuserconfigmap"></a><a href="#getuserconfigmap" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>getUserConfigMap</h4>
<p><code>getUserConfigMap</code> API gets a map of all user-defined key/value configurations for the window function.</p>
<pre><code class="hljs css language-java"><span class="hljs-comment">/**
* Get a map of all user-defined key/value configs for the function.
*
* <span class="hljs-doctag">@return</span> The full map of user-defined config values
*/</span>
<span class="hljs-function">Map&lt;String, Object&gt; <span class="hljs-title">getUserConfigMap</span><span class="hljs-params">()</span></span>;
</code></pre>
<h4><a class="anchor" aria-hidden="true" id="getuserconfigvalue"></a><a href="#getuserconfigvalue" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>getUserConfigValue</h4>
<p>The <code>getUserConfigValue</code> API gets a user-defined key/value.</p>
<pre><code class="hljs css language-java"><span class="hljs-comment">/**
* Get any user-defined key/value.
*
* <span class="hljs-doctag">@param</span> key The key
* <span class="hljs-doctag">@return</span> The Optional value specified by the user for that key.
*/</span>
<span class="hljs-function">Optional&lt;Object&gt; <span class="hljs-title">getUserConfigValue</span><span class="hljs-params">(String key)</span></span>;
</code></pre>
<h4><a class="anchor" aria-hidden="true" id="getuserconfigvalueordefault"></a><a href="#getuserconfigvalueordefault" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>getUserConfigValueOrDefault</h4>
<p>The <code>getUserConfigValueOrDefault</code> API gets a user-defined key/value or a default value if none is present.</p>
<pre><code class="hljs css language-java"><span class="hljs-comment">/**
* Get any user-defined key/value or a default value if none is present.
*
* <span class="hljs-doctag">@param</span> key
* <span class="hljs-doctag">@param</span> defaultValue
* <span class="hljs-doctag">@return</span> Either the user config value associated with a given key or a supplied default value
*/</span>
<span class="hljs-function">Object <span class="hljs-title">getUserConfigValueOrDefault</span><span class="hljs-params">(String key, Object defaultValue)</span></span>;
</code></pre>
<p>This example demonstrates how to access key/value pairs provided to Pulsar window functions.</p>
<p>Java SDK context object enables you to access key/value pairs provided to Pulsar window functions via the command line (as JSON).</p>
<blockquote>
<p><strong>Tip</strong></p>
<p>For all key/value pairs passed to Java window functions, both the <code>key</code> and the <code>value</code> are <code>String</code>. To set the value to be a different type, you need to deserialize it from the <code>String</code> type.</p>
</blockquote>
<p>This example passes a key/value pair in a Java window function.</p>
<pre><code class="hljs css language-bash">bin/pulsar-admin <span class="hljs-built_in">functions</span> create \
--user-config <span class="hljs-string">'{"word-of-the-day":"verdure"}'</span> \
<span class="hljs-comment"># Other function configs</span>
</code></pre>
<p>This example accesses values in a Java window function.</p>
<p>The <code>UserConfigFunction</code> function logs the string <code>&quot;The word of the day is verdure&quot;</code> every time the function is invoked (which means every time a message arrives). The user config of <code>word-of-the-day</code> is changed <strong>only</strong> when the function is updated with a new config value via
multiple ways, such as the command line tool or REST API.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">import</span> org.apache.pulsar.functions.api.Context;
<span class="hljs-keyword">import</span> org.apache.pulsar.functions.api.Function;
<span class="hljs-keyword">import</span> org.slf4j.Logger;
<span class="hljs-keyword">import</span> java.util.Optional;
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">UserConfigWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">String</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> String <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; input, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
Optional&lt;Object&gt; whatToWrite = context.getUserConfigValue(<span class="hljs-string">"WhatToWrite"</span>);
<span class="hljs-keyword">if</span> (whatToWrite.get() != <span class="hljs-keyword">null</span>) {
<span class="hljs-keyword">return</span> (String)whatToWrite.get();
} <span class="hljs-keyword">else</span> {
<span class="hljs-keyword">return</span> <span class="hljs-string">"Not a nice way"</span>;
}
}
}
</code></pre>
<p>If no value is provided, you can access the entire user config map or set a default value.</p>
<pre><code class="hljs css language-java"><span class="hljs-comment">// Get the whole config map</span>
Map&lt;String, String&gt; allConfigs = context.getUserConfigMap();
<span class="hljs-comment">// Get value or resort to default</span>
String wotd = context.getUserConfigValueOrDefault(<span class="hljs-string">"word-of-the-day"</span>, <span class="hljs-string">"perspicacious"</span>);
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="routing"></a><a href="#routing" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Routing</h2>
<p>You can use the <code>context.publish()</code> interface to publish as many results as you want.</p>
<p>This example shows that the <code>PublishFunction</code> class uses the built-in function in the context to publish messages to the <code>publishTopic</code> in a Java function.</p>
<pre><code class="hljs css language-java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">PublishWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; input, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
String publishTopic = (String) context.getUserConfigValueOrDefault(<span class="hljs-string">"publish-topic"</span>, <span class="hljs-string">"publishtopic"</span>);
String output = String.format(<span class="hljs-string">"%s!"</span>, input);
context.publish(publishTopic, output);
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="state-storage"></a><a href="#state-storage" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>State storage</h2>
<p>Pulsar window functions use <a href="https://bookkeeper.apache.org">Apache BookKeeper</a> as a state storage interface. Apache Pulsar installation (including the standalone installation) includes the deployment of BookKeeper bookies.</p>
<p>Apache Pulsar integrates with Apache BookKeeper <code>table service</code> to store the <code>state</code> for functions. For example, the <code>WordCount</code> function can store its <code>counters</code> state into BookKeeper table service via Pulsar Functions state APIs.</p>
<p>States are key-value pairs, where the key is a string and the value is arbitrary binary data—counters are stored as 64-bit big-endian binary values. Keys are scoped to an individual Pulsar Function and shared between instances of that function.</p>
<p>Currently, Pulsar window functions expose Java API to access, update, and manage states. These APIs are available in the context object when you use Java SDK functions.</p>
<table>
<thead>
<tr><th>Java API</th><th>Description</th></tr>
</thead>
<tbody>
<tr><td><code>incrCounter</code></td><td>Increases a built-in distributed counter referred by key.</td></tr>
<tr><td><code>getCounter</code></td><td>Gets the counter value for the key.</td></tr>
<tr><td><code>putState</code></td><td>Updates the state value for the key.</td></tr>
</tbody>
</table>
<p>You can use the following APIs to access, update, and manage states in Java window functions.</p>
<h4><a class="anchor" aria-hidden="true" id="incrcounter"></a><a href="#incrcounter" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>incrCounter</h4>
<p>The <code>incrCounter</code> API increases a built-in distributed counter referred by key.</p>
<p>Applications use the <code>incrCounter</code> API to change the counter of a given <code>key</code> by the given <code>amount</code>. If the <code>key</code> does not exist, a new key is created.</p>
<pre><code class="hljs css language-java"> <span class="hljs-comment">/**
* Increment the builtin distributed counter referred by key
* <span class="hljs-doctag">@param</span> key The name of the key
* <span class="hljs-doctag">@param</span> amount The amount to be incremented
*/</span>
<span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">incrCounter</span><span class="hljs-params">(String key, <span class="hljs-keyword">long</span> amount)</span></span>;
</code></pre>
<h4><a class="anchor" aria-hidden="true" id="getcounter"></a><a href="#getcounter" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>getCounter</h4>
<p>The <code>getCounter</code> API gets the counter value for the key.</p>
<p>Applications uses the <code>getCounter</code> API to retrieve the counter of a given <code>key</code> changed by the <code>incrCounter</code> API.</p>
<pre><code class="hljs css language-java"> <span class="hljs-comment">/**
* Retrieve the counter value for the key.
*
* <span class="hljs-doctag">@param</span> key name of the key
* <span class="hljs-doctag">@return</span> the amount of the counter value for this key
*/</span>
<span class="hljs-function"><span class="hljs-keyword">long</span> <span class="hljs-title">getCounter</span><span class="hljs-params">(String key)</span></span>;
</code></pre>
<p>Except the <code>getCounter</code> API, Pulsar also exposes a general key/value API (<code>putState</code>) for functions to store general key/value state.</p>
<h4><a class="anchor" aria-hidden="true" id="putstate"></a><a href="#putstate" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>putState</h4>
<p>The <code>putState</code> API updates the state value for the key.</p>
<pre><code class="hljs css language-java"> <span class="hljs-comment">/**
* Update the state value for the key.
*
* <span class="hljs-doctag">@param</span> key name of the key
* <span class="hljs-doctag">@param</span> value state value of the key
*/</span>
<span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">putState</span><span class="hljs-params">(String key, ByteBuffer value)</span></span>;
</code></pre>
<p>This example demonstrates how applications store states in Pulsar window functions.</p>
<p>The logic of the <code>WordCountWindowFunction</code> is simple and straightforward.</p>
<ol>
<li><p>The function first splits the received string into multiple words using regex <code>\\.</code>.</p></li>
<li><p>For each <code>word</code>, the function increments the corresponding <code>counter</code> by 1 via <code>incrCounter(key, amount)</code>.</p></li>
</ol>
<pre><code class="hljs css language-java"><span class="hljs-keyword">import</span> org.apache.pulsar.functions.api.Context;
<span class="hljs-keyword">import</span> org.apache.pulsar.functions.api.Function;
<span class="hljs-keyword">import</span> java.util.Arrays;
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">WordCountWindowFunction</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WindowFunction</span>&lt;<span class="hljs-title">String</span>, <span class="hljs-title">Void</span>&gt; </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Void <span class="hljs-title">process</span><span class="hljs-params">(Collection&lt;Record&lt;String&gt;&gt; inputs, WindowContext context)</span> <span class="hljs-keyword">throws</span> Exception </span>{
<span class="hljs-keyword">for</span> (Record&lt;String&gt; input : inputs) {
Arrays.asList(input.getValue().split(<span class="hljs-string">"\\."</span>)).forEach(word -&gt; context.incrCounter(word, <span class="hljs-number">1</span>));
}
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
</span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="/docs/en/2.4.2/functions-cli"><span class="arrow-prev">← </span><span>Reference: CLI</span></a><a class="docs-next button" href="/docs/en/2.4.2/io-overview"><span>Overview</span><span class="arrow-next"> →</span></a></div></div></div><nav class="onPageNav"><ul class="toc-headings"><li><a href="#spec">Spec</a><ul class="toc-headings"><li><a href="#get-input-topics">Get input topics</a></li><li><a href="#get-output-topic">Get output topic</a></li><li><a href="#get-tenant">Get tenant</a></li><li><a href="#get-namespace">Get namespace</a></li><li><a href="#get-function-name">Get function name</a></li><li><a href="#get-function-id">Get function ID</a></li><li><a href="#get-function-version">Get function version</a></li><li><a href="#get-instance-id">Get instance ID</a></li><li><a href="#get-num-instances">Get num instances</a></li><li><a href="#get-output-schema-type">Get output schema type</a></li></ul></li><li><a href="#logger">Logger</a></li><li><a href="#metrics">Metrics</a></li><li><a href="#user-config">User config</a><ul class="toc-headings"><li><a href="#api">API</a></li></ul></li><li><a href="#routing">Routing</a></li><li><a href="#state-storage">State storage</a></li></ul></nav></div><footer class="nav-footer" id="footer"><section class="copyright">Copyright © 2022 The Apache Software Foundation. All Rights Reserved. Apache, Apache Pulsar and the Apache feather logo are trademarks of The Apache Software Foundation.</section><span><script>
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const communityDropDown = document.getElementById("community-dropdown");
communityMenuItem.addEventListener("click", function(event) {
event.preventDefault();
if (communityDropDown.className == 'hide') {
communityDropDown.className = 'visible';
} else {
communityDropDown.className = 'hide';
}
});
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