content/2015/02/09/introducing-flink-streaming/index.html - flink-web - Git at Google


 <!DOCTYPE html>
 <html lang="en" dir=>

 <head>
   <meta name="generator" content="Hugo 0.111.3">
   <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 <meta name="description" content="This post is the first of a series of blog posts on Flink Streaming, the recent addition to Apache Flink that makes it possible to analyze continuous data sources in addition to static files. Flink Streaming uses the pipelined Flink engine to process data streams in real time and offers a new API including definition of flexible windows.
 In this post, we go through an example that uses the Flink Streaming API to compute statistics on stock market data that arrive continuously and combine the stock market data with Twitter streams.">
 <meta name="theme-color" content="#FFFFFF"><meta property="og:title" content="Introducing Flink Streaming" />
 <meta property="og:description" content="This post is the first of a series of blog posts on Flink Streaming, the recent addition to Apache Flink that makes it possible to analyze continuous data sources in addition to static files. Flink Streaming uses the pipelined Flink engine to process data streams in real time and offers a new API including definition of flexible windows.
 In this post, we go through an example that uses the Flink Streaming API to compute statistics on stock market data that arrive continuously and combine the stock market data with Twitter streams." />
 <meta property="og:type" content="article" />
 <meta property="og:url" content="https://flink.apache.org/2015/02/09/introducing-flink-streaming/" /><meta property="article:section" content="posts" />
 <meta property="article:published_time" content="2015-02-09T12:00:00+00:00" />
 <meta property="article:modified_time" content="2015-02-09T12:00:00+00:00" />
 <title>Introducing Flink Streaming | Apache Flink</title>
 <link rel="manifest" href="/manifest.json">
 <link rel="icon" href="/favicon.png" type="image/x-icon">
 <link rel="stylesheet" href="/book.min.e3b33391dbc1f4b2cc47778e2f4b86c744ded3ccc82fdfb6f08caf91d8607f9a.css" integrity="sha256-47MzkdvB9LLMR3eOL0uGx0Te08zIL9&#43;28Iyvkdhgf5o=">
 <script defer src="/en.search.min.8592fd2e43835d2ef6fab8eb9b8969ee6ad1bdb888a636e37e28032f8bd9887d.js" integrity="sha256-hZL9LkODXS72&#43;rjrm4lp7mrRvbiIpjbjfigDL4vZiH0="></script>
 <!--
 Made with Book Theme
 https://github.com/alex-shpak/hugo-book
 -->


 <link rel="stylesheet" type="text/css" href="/font-awesome/css/font-awesome.min.css">
 <script src="/js/anchor.min.js"></script>
 <script src="/js/flink.js"></script>
 <link rel="canonical" href="https://flink.apache.org/2015/02/09/introducing-flink-streaming/">


     <script>
       var _paq = window._paq = window._paq || [];


       _paq.push(['disableCookies']);

       _paq.push(["setDomains", ["*.flink.apache.org","*.nightlies.apache.org/flink"]]);
       _paq.push(['trackPageView']);
       _paq.push(['enableLinkTracking']);
       (function() {
         var u="//analytics.apache.org/";
         _paq.push(['setTrackerUrl', u+'matomo.php']);
         _paq.push(['setSiteId', '1']);
         var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0];
         g.async=true; g.src=u+'matomo.js'; s.parentNode.insertBefore(g,s);
       })();
     </script>

 </head>

 <body dir=>
   <input type="checkbox" class="hidden toggle" id="menu-control" />
   <input type="checkbox" class="hidden toggle" id="toc-control" />
   <main class="container flex">
     <aside class="book-menu">


 <nav>


 <a id="logo" href="/">
     <img width="70%" src="/flink-header-logo.svg">
 </a>

 <div class="book-search">
   <input type="text" id="book-search-input" placeholder="Search" aria-label="Search" maxlength="64" data-hotkeys="s/" />
   <div class="book-search-spinner hidden"></div>
   <ul id="book-search-results"></ul>
 </div>


   <input type="checkbox" id="section-4117fb24454a2c30ee86e524839e77ec" class="toggle"  />
   <label for="section-4117fb24454a2c30ee86e524839e77ec" class="flex justify-between flink-menu-item">What is Apache Flink?<span>▾</span>
   </label>

     <ul>

       <li>


     <label for="section-ffd5922da551e96e0481423fab94c463" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="/what-is-flink/flink-architecture/" class="">Architecture</a>
     </label>


       </li>

       <li>


     <label for="section-fc28f08b67476edb77e00e03b6c7c2e0" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="/what-is-flink/flink-applications/" class="">Applications</a>
     </label>


       </li>

       <li>


     <label for="section-612df33a02d5d4ee78d718abaab5b5b4" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="/what-is-flink/flink-operations/" class="">Operations</a>
     </label>


       </li>

     </ul>


 <label for="section-f1ecec07350bd6810050d40158878749" class="flex justify-between flink-menu-item">
     <a href="https://nightlies.apache.org/flink/flink-statefun-docs-stable/" style="color:black" class="">What is Stateful Functions? <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


 <label for="section-4113a4c3072cb35f6fd7a0d4e098ee70" class="flex justify-between flink-menu-item">
     <a href="https://nightlies.apache.org/flink/flink-ml-docs-stable/" style="color:black" class="">What is Flink ML? <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


 <label for="section-b39c70259d0abbe2bf1d8d645425f84d" class="flex justify-between flink-menu-item">
     <a href="https://nightlies.apache.org/flink/flink-kubernetes-operator-docs-stable/" style="color:black" class="">What is the Flink Kubernetes Operator? <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


 <label for="section-53e0b1afcb9ccaf779dc285aa272a014" class="flex justify-between flink-menu-item">
     <a href="https://nightlies.apache.org/flink/flink-table-store-docs-stable/" style="color:black" class="">What is Flink Table Store? <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


     <label for="section-f4973f06a66f063045b4ebdacaf3127d" class="flex justify-between flink-menu-item">
     <a href="/use-cases/" class="">Use Cases</a>
     </label>


     <label for="section-0f1863835376e859ac438ae9529daff2" class="flex justify-between flink-menu-item">
     <a href="/powered-by/" class="">Powered By</a>
     </label>


   <br/>


     <label for="section-f383f23a96a43d8d0cc66aeb0237e26a" class="flex justify-between flink-menu-item">
     <a href="/downloads/" class="">Downloads</a>
     </label>


   <input type="checkbox" id="section-c727fab97b4d77e5b28ce8c448fb9000" class="toggle"  />
   <label for="section-c727fab97b4d77e5b28ce8c448fb9000" class="flex justify-between flink-menu-item">Getting Started<span>▾</span>
   </label>

     <ul>

       <li>


 <label for="section-f45abaa99ab076108b9a5b94edbc6647" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-docs-stable/docs/try-flink/local_installation/" style="color:black" class="">With Flink <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-efe2166e9dce6f72e126dcc2396b4402" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-statefun-docs-stable/getting-started/project-setup.html" style="color:black" class="">With Flink Stateful Functions <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-7e268d0a469b1093bb33d71d093eb7b9" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-ml-docs-stable/docs/try-flink-ml/quick-start/" style="color:black" class="">With Flink ML <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-cc7147cd0441503127bfaf6f219d4fbb" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-kubernetes-operator-docs-stable/docs/try-flink-kubernetes-operator/quick-start/" style="color:black" class="">With Flink Kubernetes Operator <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-660ca694e416d8ca9176dda52a60d637" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-table-store-docs-stable/docs/try-table-store/quick-start/" style="color:black" class="">With Flink Table Store <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-75db0b47bf4ae9c247aadbba5fbd720d" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-docs-stable/docs/learn-flink/overview/" style="color:black" class="">Training Course <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

     </ul>


   <input type="checkbox" id="section-6318075fef29529089951a49d413d083" class="toggle"  />
   <label for="section-6318075fef29529089951a49d413d083" class="flex justify-between flink-menu-item">Documentation<span>▾</span>
   </label>

     <ul>

       <li>


 <label for="section-9a8122d8912450484d1c25394ad40229" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-docs-stable/" style="color:black" class="">Flink 1.17 (stable) <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-8b2fd3efb702be3783ba98d650707e3c" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-docs-master/" style="color:black" class="">Flink Master (snapshot) <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-5317a079cddb964c59763c27607f43d9" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-statefun-docs-stable/" style="color:black" class="">Stateful Functions 3.2 (stable) <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-25b72f108b7156e94d91b04853d8813a" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-statefun-docs-master" style="color:black" class="">Stateful Functions Master (snapshot) <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-13a02f969904a2455a39ed90e287593f" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-ml-docs-stable/" style="color:black" class="">ML 2.2 (stable) <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-6d895ec5ad127a29a6a9ce101328ccdf" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-ml-docs-master" style="color:black" class="">ML Master (snapshot) <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-c83ad0caf34e364bf3729badd233a350" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-kubernetes-operator-docs-stable/" style="color:black" class="">Kubernetes Operator 1.4 (latest) <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-a2c75d90005425982ba8f26ae0e160a3" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-kubernetes-operator-docs-main" style="color:black" class="">Kubernetes Operator Main (snapshot) <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-07b85e4b2f61b1526bf202c64460abcd" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-table-store-docs-stable/" style="color:black" class="">Table Store 0.3 (stable) <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

       <li>


 <label for="section-9b9a0032b1e858a34c125d828d1a0718" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="https://nightlies.apache.org/flink/flink-table-store-docs-master/" style="color:black" class="">Table Store Master (snapshot) <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


       </li>

     </ul>


     <label for="section-63d6a565d79aa2895f70806a46021c07" class="flex justify-between flink-menu-item">
     <a href="/getting-help/" class="">Getting Help</a>
     </label>


 <label for="section-1d5066022b83f4732dc80f4e9eaa069a" class="flex justify-between flink-menu-item">
     <a href="https://flink-packages.org/" style="color:black" class="">flink-packages.org <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


   <br/>


     <label for="section-7821b78a97db9e919426e86121a7be9c" class="flex justify-between flink-menu-item">
     <a href="/community/" class="">Community & Project Info</a>
     </label>


     <label for="section-8c042831df4e371c4ef9375f1df06f35" class="flex justify-between flink-menu-item">
     <a href="/roadmap/" class="">Roadmap</a>
     </label>


   <input type="checkbox" id="section-73117efde5302fddcb193307d582b588" class="toggle"  />
   <label for="section-73117efde5302fddcb193307d582b588" class="flex justify-between flink-menu-item">How to Contribute<span>▾</span>
   </label>

     <ul>

       <li>


     <label for="section-6646b26b23a3e79b8de9c552ee76f6dd" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="/how-to-contribute/overview/" class="">Overview</a>
     </label>


       </li>

       <li>


     <label for="section-e6ab9538b82cd5f94103b971adb7c1a9" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="/how-to-contribute/contribute-code/" class="">Contribute Code</a>
     </label>


       </li>

       <li>


     <label for="section-1c09e1358485e82d9b3f5f689d4ced65" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="/how-to-contribute/reviewing-prs/" class="">Review Pull Requests</a>
     </label>


       </li>

       <li>


     <label for="section-ed01e0defd235498fa3c9a2a0b3302fb" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="/how-to-contribute/code-style-and-quality-preamble/" class="">Code Style and Quality Guide</a>
     </label>


       </li>

       <li>


     <label for="section-4e8d5e9924cf15f397711b0d82e15650" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="/how-to-contribute/contribute-documentation/" class="">Contribute Documentation</a>
     </label>


       </li>

       <li>


     <label for="section-ddaa8307917e5ba7f60ba3316711e492" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="/how-to-contribute/documentation-style-guide/" class="">Documentation Style Guide</a>
     </label>


       </li>

       <li>


     <label for="section-390a72c171cc82f180a308b95fc3aa72" class="flex justify-between flink-menu-item flink-menu-child">
     <a href="/how-to-contribute/improve-website/" class="">Contribute to the Website</a>
     </label>


       </li>

     </ul>


     <label for="section-9d3ddfd487223d5a199ba301f25c88c6" class="flex justify-between flink-menu-item">
     <a href="/security/" class="">Security</a>
     </label>


   <br/>


     <label for="section-a07783f405300745807d39eacf150420" class="flex justify-between flink-menu-item">
     <a href="/posts/" class="">Flink Blog</a>
     </label>


 <br/>
 <hr class="menu-break">


 <label for="section-f71a7070dbb7b669824a6441408ded70" class="flex justify-between flink-menu-item">
     <a href="https://github.com/apache/flink" style="color:black" class="">Flink on GitHub <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


 <label for="section-2ccaaab8c67f3105bbf7df75faca8027" class="flex justify-between flink-menu-item">
     <a href="https://twitter.com/apacheflink" style="color:black" class="">@ApacheFlink <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label>


 <hr class="menu-break">
 <table>
   <tr>
     <th colspan="2">
 <label for="section-78c2028200542d78f8c1a8f6b4cbb36b" class="flex justify-between flink-menu-item">
     <a href="https://www.apache.org/" style="color:black" class="">Apache Software Foundation <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label></th>
   </tr>
   <tr>
     <td>
 <label for="section-794df3791a8c800841516007427a2aa3" class="flex justify-between flink-menu-item">
     <a href="https://www.apache.org/licenses/" style="color:black" class="">License <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label></td>
     <td>
 <label for="section-2fae32629d4ef4fc6341f1751b405e45" class="flex justify-between flink-menu-item">
     <a href="https://www.apache.org/security/" style="color:black" class="">Security <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label></td>
   </tr>
   <tr>
     <td>
 <label for="section-0584e445d656b83b431227bb80ff0c30" class="flex justify-between flink-menu-item">
     <a href="https://www.apache.org/foundation/sponsorship.html" style="color:black" class="">Donate <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label></td>
     <td>
 <label for="section-00d06796e489999226fb5bb27fe1b3b2" class="flex justify-between flink-menu-item">
     <a href="https://www.apache.org/foundation/thanks.html" style="color:black" class="">Thanks <i class="link fa fa-external-link title" aria-hidden="true"></i></a>
 </label></td>
   </tr>
 </table>

 <hr class="menu-break">


 <a  href="/zh/" class="flex align-center">
   <i class="fa fa-globe" aria-hidden="true"></i>&nbsp;&nbsp;
   中文版
 </a>

 <script src="/js/track-search-terms.js"></script>


 </nav>


   <script>(function(){var e=document.querySelector("aside.book-menu nav");addEventListener("beforeunload",function(){localStorage.setItem("menu.scrollTop",e.scrollTop)}),e.scrollTop=localStorage.getItem("menu.scrollTop")})()</script>


     </aside>

     <div class="book-page">
       <header class="book-header">

   <div class="flex align-center justify-between">
   <label for="menu-control">
     <img src="/svg/menu.svg" class="book-icon" alt="Menu" />
   </label>

   <strong>Introducing Flink Streaming</strong>

   <label for="toc-control">

     <img src="/svg/toc.svg" class="book-icon" alt="Table of Contents" />

   </label>
 </div>


   <aside class="hidden clearfix">


 <nav id="TableOfContents"><h3>On This Page <button class="toc" onclick="collapseToc()"><i class="fa fa-compress" aria-hidden="true"></i></button></h3>
   <ul>
     <li><a href="#reading-from-multiple-inputs">Reading from multiple inputs</a></li>
     <li><a href="#window-aggregations">Window aggregations</a></li>
     <li><a href="#data-driven-windows">Data-driven windows</a></li>
     <li><a href="#combining-with-a-twitter-stream">Combining with a Twitter stream</a></li>
     <li><a href="#streaming-joins">Streaming joins</a></li>
     <li><a href="#other-things-to-try">Other things to try</a></li>
     <li><a href="#upcoming-for-streaming">Upcoming for streaming</a></li>
   </ul>
 </nav>


   </aside>


       </header>


 <article class="markdown">
     <h1>
         <a href="/2015/02/09/introducing-flink-streaming/">Introducing Flink Streaming</a>
     </h1>

   February 9, 2015 -


     <p><p>This post is the first of a series of blog posts on Flink Streaming,
 the recent addition to Apache Flink that makes it possible to analyze
 continuous data sources in addition to static files. Flink Streaming
 uses the pipelined Flink engine to process data streams in real time
 and offers a new API including definition of flexible windows.</p>
 <p>In this post, we go through an example that uses the Flink Streaming
 API to compute statistics on stock market data that arrive
 continuously and combine the stock market data with Twitter streams.
 See the <a href="//nightlies.apache.org/flinkflink-docs-master/apis/streaming/index.html">Streaming Programming
 Guide</a> for a
 detailed presentation of the Streaming API.</p>
 <p>First, we read a bunch of stock price streams and combine them into
 one stream of market data. We apply several transformations on this
 market data stream, like rolling aggregations per stock. Then we emit
 price warning alerts when the prices are rapidly changing. Moving
 towards more advanced features, we compute rolling correlations
 between the market data streams and a Twitter stream with stock mentions.</p>
 <p>For running the example implementation please use the <em>0.9-SNAPSHOT</em>
 version of Flink as a dependency. The full example code base can be
 found <a href="https://github.com/mbalassi/flink/blob/stockprices/flink-staging/flink-streaming/flink-streaming-examples/src/main/scala/org/apache/flink/streaming/scala/examples/windowing/StockPrices.scala">here</a> in Scala and <a href="https://github.com/mbalassi/flink/blob/stockprices/flink-staging/flink-streaming/flink-streaming-examples/src/main/java/org/apache/flink/streaming/examples/windowing/StockPrices.java">here</a> in Java7.</p>
 <p><a href="#top"></a></p>
 <p><a href="#top">Back to top</a></p>
 <h2 id="reading-from-multiple-inputs">
   Reading from multiple inputs
   <a class="anchor" href="#reading-from-multiple-inputs">#</a>
 </h2>
 <p>First, let us create the stream of stock prices:</p>
 <ol>
 <li>Read a socket stream of stock prices</li>
 <li>Parse the text in the stream to create a stream of <code>StockPrice</code> objects</li>
 <li>Add four other sources tagged with the stock symbol.</li>
 <li>Finally, merge the streams to create a unified stream.</li>
 </ol>
 <img alt="Reading from multiple inputs" src="/img/blog/blog_multi_input.png" width="70%" class="img-responsive center-block">
 <div class="codetabs" markdown="1">
 <div data-lang="scala" markdown="1">
 <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-scala" data-lang="scala"><span class="line"><span class="cl"><span class="k">def</span> <span class="n">main</span><span class="o">(</span><span class="n">args</span><span class="k">:</span> <span class="kt">Array</span><span class="o">[</span><span class="kt">String</span><span class="o">])</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">  <span class="k">val</span> <span class="n">env</span> <span class="k">=</span> <span class="nc">StreamExecutionEnvironment</span><span class="o">.</span><span class="n">getExecutionEnvironment</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">  <span class="c1">//Read from a socket stream at map it to StockPrice objects
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span>  <span class="k">val</span> <span class="n">socketStockStream</span> <span class="k">=</span> <span class="n">env</span><span class="o">.</span><span class="n">socketTextStream</span><span class="o">(</span><span class="s">&#34;localhost&#34;</span><span class="o">,</span> <span class="mi">9999</span><span class="o">).</span><span class="n">map</span><span class="o">(</span><span class="n">x</span> <span class="k">=&gt;</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="k">val</span> <span class="n">split</span> <span class="k">=</span> <span class="n">x</span><span class="o">.</span><span class="n">split</span><span class="o">(</span><span class="s">&#34;,&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">    <span class="nc">StockPrice</span><span class="o">(</span><span class="n">split</span><span class="o">(</span><span class="mi">0</span><span class="o">),</span> <span class="n">split</span><span class="o">(</span><span class="mi">1</span><span class="o">).</span><span class="n">toDouble</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">  <span class="o">})</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">  <span class="c1">//Generate other stock streams
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span>  <span class="k">val</span> <span class="nc">SPX_Stream</span> <span class="k">=</span> <span class="n">env</span><span class="o">.</span><span class="n">addSource</span><span class="o">(</span><span class="n">generateStock</span><span class="o">(</span><span class="s">&#34;SPX&#34;</span><span class="o">)(</span><span class="mi">10</span><span class="o">)</span> <span class="k">_</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">  <span class="k">val</span> <span class="nc">FTSE_Stream</span> <span class="k">=</span> <span class="n">env</span><span class="o">.</span><span class="n">addSource</span><span class="o">(</span><span class="n">generateStock</span><span class="o">(</span><span class="s">&#34;FTSE&#34;</span><span class="o">)(</span><span class="mi">20</span><span class="o">)</span> <span class="k">_</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">  <span class="k">val</span> <span class="nc">DJI_Stream</span> <span class="k">=</span> <span class="n">env</span><span class="o">.</span><span class="n">addSource</span><span class="o">(</span><span class="n">generateStock</span><span class="o">(</span><span class="s">&#34;DJI&#34;</span><span class="o">)(</span><span class="mi">30</span><span class="o">)</span> <span class="k">_</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">  <span class="k">val</span> <span class="nc">BUX_Stream</span> <span class="k">=</span> <span class="n">env</span><span class="o">.</span><span class="n">addSource</span><span class="o">(</span><span class="n">generateStock</span><span class="o">(</span><span class="s">&#34;BUX&#34;</span><span class="o">)(</span><span class="mi">40</span><span class="o">)</span> <span class="k">_</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">  <span class="c1">//Merge all stock streams together
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span>  <span class="k">val</span> <span class="n">stockStream</span> <span class="k">=</span> <span class="n">socketStockStream</span><span class="o">.</span><span class="n">merge</span><span class="o">(</span><span class="nc">SPX_Stream</span><span class="o">,</span> <span class="nc">FTSE_Stream</span><span class="o">,</span>
 </span></span><span class="line"><span class="cl">    <span class="nc">DJI_Stream</span><span class="o">,</span> <span class="nc">BUX_Stream</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">  <span class="n">stockStream</span><span class="o">.</span><span class="n">print</span><span class="o">()</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">  <span class="n">env</span><span class="o">.</span><span class="n">execute</span><span class="o">(</span><span class="s">&#34;Stock stream&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span></span></span></code></pre></div>
 </div>
 <div data-lang="java7" markdown="1">
 <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">static</span> <span class="kt">void</span> <span class="nf">main</span><span class="o">(</span><span class="n">String</span><span class="o">[]</span> <span class="n">args</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="kd">final</span> <span class="n">StreamExecutionEnvironment</span> <span class="n">env</span> <span class="o">=</span>
 </span></span><span class="line"><span class="cl">        <span class="n">StreamExecutionEnvironment</span><span class="o">.</span><span class="na">getExecutionEnvironment</span><span class="o">();</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="c1">//Read from a socket stream at map it to StockPrice objects
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span>    <span class="n">DataStream</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">socketStockStream</span> <span class="o">=</span> <span class="n">env</span>
 </span></span><span class="line"><span class="cl">            <span class="o">.</span><span class="na">socketTextStream</span><span class="o">(</span><span class="s">&#34;localhost&#34;</span><span class="o">,</span> <span class="mi">9999</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">            <span class="o">.</span><span class="na">map</span><span class="o">(</span><span class="k">new</span> <span class="n">MapFunction</span><span class="o">&lt;</span><span class="n">String</span><span class="o">,</span> <span class="n">StockPrice</span><span class="o">&gt;()</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">                <span class="kd">private</span> <span class="n">String</span><span class="o">[]</span> <span class="n">tokens</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">                <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">                <span class="kd">public</span> <span class="n">StockPrice</span> <span class="nf">map</span><span class="o">(</span><span class="n">String</span> <span class="n">value</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">                    <span class="n">tokens</span> <span class="o">=</span> <span class="n">value</span><span class="o">.</span><span class="na">split</span><span class="o">(</span><span class="s">&#34;,&#34;</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">                    <span class="k">return</span> <span class="k">new</span> <span class="n">StockPrice</span><span class="o">(</span><span class="n">tokens</span><span class="o">[</span><span class="mi">0</span><span class="o">],</span>
 </span></span><span class="line"><span class="cl">                        <span class="n">Double</span><span class="o">.</span><span class="na">parseDouble</span><span class="o">(</span><span class="n">tokens</span><span class="o">[</span><span class="mi">1</span><span class="o">]));</span>
 </span></span><span class="line"><span class="cl">                <span class="o">}</span>
 </span></span><span class="line"><span class="cl">            <span class="o">});</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="c1">//Generate other stock streams
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span>    <span class="n">DataStream</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">SPX_stream</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="na">addSource</span><span class="o">(</span><span class="k">new</span> <span class="n">StockSource</span><span class="o">(</span><span class="s">&#34;SPX&#34;</span><span class="o">,</span> <span class="mi">10</span><span class="o">));</span>
 </span></span><span class="line"><span class="cl">    <span class="n">DataStream</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">FTSE_stream</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="na">addSource</span><span class="o">(</span><span class="k">new</span> <span class="n">StockSource</span><span class="o">(</span><span class="s">&#34;FTSE&#34;</span><span class="o">,</span> <span class="mi">20</span><span class="o">));</span>
 </span></span><span class="line"><span class="cl">    <span class="n">DataStream</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">DJI_stream</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="na">addSource</span><span class="o">(</span><span class="k">new</span> <span class="n">StockSource</span><span class="o">(</span><span class="s">&#34;DJI&#34;</span><span class="o">,</span> <span class="mi">30</span><span class="o">));</span>
 </span></span><span class="line"><span class="cl">    <span class="n">DataStream</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">BUX_stream</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="na">addSource</span><span class="o">(</span><span class="k">new</span> <span class="n">StockSource</span><span class="o">(</span><span class="s">&#34;BUX&#34;</span><span class="o">,</span> <span class="mi">40</span><span class="o">));</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="c1">//Merge all stock streams together
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span>    <span class="n">DataStream</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">stockStream</span> <span class="o">=</span> <span class="n">socketStockStream</span>
 </span></span><span class="line"><span class="cl">        <span class="o">.</span><span class="na">merge</span><span class="o">(</span><span class="n">SPX_stream</span><span class="o">,</span> <span class="n">FTSE_stream</span><span class="o">,</span> <span class="n">DJI_stream</span><span class="o">,</span> <span class="n">BUX_stream</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="n">stockStream</span><span class="o">.</span><span class="na">print</span><span class="o">();</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="n">env</span><span class="o">.</span><span class="na">execute</span><span class="o">(</span><span class="s">&#34;Stock stream&#34;</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">    </span></span></code></pre></div>
 </div>
 </div>
 <p>See
 <a href="//nightlies.apache.org/flinkflink-docs-master/apis/streaming/index.html#data-sources">here</a>
 on how you can create streaming sources for Flink Streaming
 programs. Flink, of course, has support for reading in streams from
 <a href="//nightlies.apache.org/flinkflink-docs-master/apis/streaming/connectors/index.html">external
 sources</a>
 such as Apache Kafka, Apache Flume, RabbitMQ, and others. For the sake
 of this example, the data streams are simply generated using the
 <code>generateStock</code> method:</p>
 <div class="codetabs" markdown="1">
 <div data-lang="scala" markdown="1">
 <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-scala" data-lang="scala"><span class="line"><span class="cl"><span class="k">val</span> <span class="n">symbols</span> <span class="k">=</span> <span class="nc">List</span><span class="o">(</span><span class="s">&#34;SPX&#34;</span><span class="o">,</span> <span class="s">&#34;FTSE&#34;</span><span class="o">,</span> <span class="s">&#34;DJI&#34;</span><span class="o">,</span> <span class="s">&#34;DJT&#34;</span><span class="o">,</span> <span class="s">&#34;BUX&#34;</span><span class="o">,</span> <span class="s">&#34;DAX&#34;</span><span class="o">,</span> <span class="s">&#34;GOOG&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="k">case</span> <span class="k">class</span> <span class="nc">StockPrice</span><span class="o">(</span><span class="n">symbol</span><span class="k">:</span> <span class="kt">String</span><span class="o">,</span> <span class="n">price</span><span class="k">:</span> <span class="kt">Double</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="k">def</span> <span class="n">generateStock</span><span class="o">(</span><span class="n">symbol</span><span class="k">:</span> <span class="kt">String</span><span class="o">)(</span><span class="n">sigma</span><span class="k">:</span> <span class="kt">Int</span><span class="o">)(</span><span class="n">out</span><span class="k">:</span> <span class="kt">Collector</span><span class="o">[</span><span class="kt">StockPrice</span><span class="o">])</span> <span class="k">=</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">  <span class="k">var</span> <span class="n">price</span> <span class="k">=</span> <span class="mf">1000.</span>
 </span></span><span class="line"><span class="cl">  <span class="k">while</span> <span class="o">(</span><span class="kc">true</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="n">price</span> <span class="k">=</span> <span class="n">price</span> <span class="o">+</span> <span class="nc">Random</span><span class="o">.</span><span class="n">nextGaussian</span> <span class="o">*</span> <span class="n">sigma</span>
 </span></span><span class="line"><span class="cl">    <span class="n">out</span><span class="o">.</span><span class="n">collect</span><span class="o">(</span><span class="nc">StockPrice</span><span class="o">(</span><span class="n">symbol</span><span class="o">,</span> <span class="n">price</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">    <span class="nc">Thread</span><span class="o">.</span><span class="n">sleep</span><span class="o">(</span><span class="nc">Random</span><span class="o">.</span><span class="n">nextInt</span><span class="o">(</span><span class="mi">200</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">  <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span></span></span></code></pre></div>
 </div>
 <div data-lang="java7" markdown="1">
 <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">ArrayList</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="n">SYMBOLS</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ArrayList</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;(</span>
 </span></span><span class="line"><span class="cl">    <span class="n">Arrays</span><span class="o">.</span><span class="na">asList</span><span class="o">(</span><span class="s">&#34;SPX&#34;</span><span class="o">,</span> <span class="s">&#34;FTSE&#34;</span><span class="o">,</span> <span class="s">&#34;DJI&#34;</span><span class="o">,</span> <span class="s">&#34;DJT&#34;</span><span class="o">,</span> <span class="s">&#34;BUX&#34;</span><span class="o">,</span> <span class="s">&#34;DAX&#34;</span><span class="o">,</span> <span class="s">&#34;GOOG&#34;</span><span class="o">));</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">static</span> <span class="kd">class</span> <span class="nc">StockPrice</span> <span class="kd">implements</span> <span class="n">Serializable</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="n">String</span> <span class="n">symbol</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="n">Double</span> <span class="n">price</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="nf">StockPrice</span><span class="o">()</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="nf">StockPrice</span><span class="o">(</span><span class="n">String</span> <span class="n">symbol</span><span class="o">,</span> <span class="n">Double</span> <span class="n">price</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">        <span class="k">this</span><span class="o">.</span><span class="na">symbol</span> <span class="o">=</span> <span class="n">symbol</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">        <span class="k">this</span><span class="o">.</span><span class="na">price</span> <span class="o">=</span> <span class="n">price</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="n">String</span> <span class="nf">toString</span><span class="o">()</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">        <span class="k">return</span> <span class="s">&#34;StockPrice{&#34;</span> <span class="o">+</span>
 </span></span><span class="line"><span class="cl">                <span class="s">&#34;symbol=&#39;&#34;</span> <span class="o">+</span> <span class="n">symbol</span> <span class="o">+</span> <span class="sc">&#39;\&#39;&#39;</span> <span class="o">+</span>
 </span></span><span class="line"><span class="cl">                <span class="s">&#34;, count=&#34;</span> <span class="o">+</span> <span class="n">price</span> <span class="o">+</span>
 </span></span><span class="line"><span class="cl">                <span class="sc">&#39;}&#39;</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">final</span> <span class="kd">static</span> <span class="kd">class</span> <span class="nc">StockSource</span> <span class="kd">implements</span> <span class="n">SourceFunction</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">Double</span> <span class="n">price</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">String</span> <span class="n">symbol</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">Integer</span> <span class="n">sigma</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="nf">StockSource</span><span class="o">(</span><span class="n">String</span> <span class="n">symbol</span><span class="o">,</span> <span class="n">Integer</span> <span class="n">sigma</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">        <span class="k">this</span><span class="o">.</span><span class="na">symbol</span> <span class="o">=</span> <span class="n">symbol</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">        <span class="k">this</span><span class="o">.</span><span class="na">sigma</span> <span class="o">=</span> <span class="n">sigma</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kt">void</span> <span class="nf">invoke</span><span class="o">(</span><span class="n">Collector</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">collector</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">        <span class="n">price</span> <span class="o">=</span> <span class="n">DEFAULT_PRICE</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">        <span class="n">Random</span> <span class="n">random</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Random</span><span class="o">();</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">        <span class="k">while</span> <span class="o">(</span><span class="kc">true</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">            <span class="n">price</span> <span class="o">=</span> <span class="n">price</span> <span class="o">+</span> <span class="n">random</span><span class="o">.</span><span class="na">nextGaussian</span><span class="o">()</span> <span class="o">*</span> <span class="n">sigma</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">            <span class="n">collector</span><span class="o">.</span><span class="na">collect</span><span class="o">(</span><span class="k">new</span> <span class="n">StockPrice</span><span class="o">(</span><span class="n">symbol</span><span class="o">,</span> <span class="n">price</span><span class="o">));</span>
 </span></span><span class="line"><span class="cl">            <span class="n">Thread</span><span class="o">.</span><span class="na">sleep</span><span class="o">(</span><span class="n">random</span><span class="o">.</span><span class="na">nextInt</span><span class="o">(</span><span class="mi">200</span><span class="o">));</span>
 </span></span><span class="line"><span class="cl">        <span class="o">}</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span></span></span></code></pre></div>
 </div>
 </div>
 <p>To read from the text socket stream please make sure that you have a
 socket running. For the sake of the example executing the following
 command in a terminal does the job. You can get
 <a href="http://netcat.sourceforge.net/">netcat</a> here if it is not available
 on your machine.</p>
 <pre tabindex="0"><code>nc -lk 9999
 </code></pre><p>If we execute the program from our IDE we see the system the
 stock prices being generated:</p>
 <pre tabindex="0"><code>INFO    Job execution switched to status RUNNING.
 INFO    Socket Stream(1/1) switched to SCHEDULED
 INFO    Socket Stream(1/1) switched to DEPLOYING
 INFO    Custom Source(1/1) switched to SCHEDULED
 INFO    Custom Source(1/1) switched to DEPLOYING
 …
 1&gt; StockPrice{symbol=&#39;SPX&#39;, count=1011.3405732645239}
 2&gt; StockPrice{symbol=&#39;SPX&#39;, count=1018.3381290039248}
 1&gt; StockPrice{symbol=&#39;DJI&#39;, count=1036.7454894073978}
 3&gt; StockPrice{symbol=&#39;DJI&#39;, count=1135.1170217478427}
 3&gt; StockPrice{symbol=&#39;BUX&#39;, count=1053.667523187687}
 4&gt; StockPrice{symbol=&#39;BUX&#39;, count=1036.552601487263}
 </code></pre><p><a href="#top">Back to top</a></p>
 <h2 id="window-aggregations">
   Window aggregations
   <a class="anchor" href="#window-aggregations">#</a>
 </h2>
 <p>We first compute aggregations on time-based windows of the
 data. Flink provides <a href="//nightlies.apache.org/flinkflink-docs-master/apis/streaming/windows.html">flexible windowing semantics</a> where windows can
 also be defined based on count of records or any custom user defined
 logic.</p>
 <p>We partition our stream into windows of 10 seconds and slide the
 window every 5 seconds. We compute three statistics every 5 seconds.
 The first is the minimum price of all stocks, the second produces
 maximum price per stock, and the third is the mean stock price
 (using a map window function). Aggregations and groupings can be
 performed on named fields of POJOs, making the code more readable.</p>
 <img alt="Basic windowing aggregations" src="/img/blog/blog_basic_window.png" width="70%" class="img-responsive center-block">
 <div class="codetabs" markdown="1">
 <div data-lang="scala" markdown="1">
 <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-scala" data-lang="scala"><span class="line"><span class="cl"><span class="c1">//Define the desired time window
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="k">val</span> <span class="n">windowedStream</span> <span class="k">=</span> <span class="n">stockStream</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">window</span><span class="o">(</span><span class="nc">Time</span><span class="o">.</span><span class="n">of</span><span class="o">(</span><span class="mi">10</span><span class="o">,</span> <span class="nc">SECONDS</span><span class="o">)).</span><span class="n">every</span><span class="o">(</span><span class="nc">Time</span><span class="o">.</span><span class="n">of</span><span class="o">(</span><span class="mi">5</span><span class="o">,</span> <span class="nc">SECONDS</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Compute some simple statistics on a rolling window
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="k">val</span> <span class="n">lowest</span> <span class="k">=</span> <span class="n">windowedStream</span><span class="o">.</span><span class="n">minBy</span><span class="o">(</span><span class="s">&#34;price&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl"><span class="k">val</span> <span class="n">maxByStock</span> <span class="k">=</span> <span class="n">windowedStream</span><span class="o">.</span><span class="n">groupBy</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">).</span><span class="n">maxBy</span><span class="o">(</span><span class="s">&#34;price&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl"><span class="k">val</span> <span class="n">rollingMean</span> <span class="k">=</span> <span class="n">windowedStream</span><span class="o">.</span><span class="n">groupBy</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">).</span><span class="n">mapWindow</span><span class="o">(</span><span class="n">mean</span> <span class="k">_</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Compute the mean of a window
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="k">def</span> <span class="n">mean</span><span class="o">(</span><span class="n">ts</span><span class="k">:</span> <span class="kt">Iterable</span><span class="o">[</span><span class="kt">StockPrice</span><span class="o">],</span> <span class="n">out</span><span class="k">:</span> <span class="kt">Collector</span><span class="o">[</span><span class="kt">StockPrice</span><span class="o">])</span> <span class="k">=</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">  <span class="k">if</span> <span class="o">(</span><span class="n">ts</span><span class="o">.</span><span class="n">nonEmpty</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="n">out</span><span class="o">.</span><span class="n">collect</span><span class="o">(</span><span class="nc">StockPrice</span><span class="o">(</span><span class="n">ts</span><span class="o">.</span><span class="n">head</span><span class="o">.</span><span class="n">symbol</span><span class="o">,</span> <span class="n">ts</span><span class="o">.</span><span class="n">foldLeft</span><span class="o">(</span><span class="mi">0</span><span class="k">:</span> <span class="kt">Double</span><span class="o">)(</span><span class="k">_</span> <span class="o">+</span> <span class="k">_</span><span class="o">.</span><span class="n">price</span><span class="o">)</span> <span class="o">/</span> <span class="n">ts</span><span class="o">.</span><span class="n">size</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">  <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span></span></span></code></pre></div>
 </div>
 <div data-lang="java7" markdown="1">
 <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="c1">//Define the desired time window
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="n">WindowedDataStream</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">windowedStream</span> <span class="o">=</span> <span class="n">stockStream</span>
 </span></span><span class="line"><span class="cl">    <span class="o">.</span><span class="na">window</span><span class="o">(</span><span class="n">Time</span><span class="o">.</span><span class="na">of</span><span class="o">(</span><span class="mi">10</span><span class="o">,</span> <span class="n">TimeUnit</span><span class="o">.</span><span class="na">SECONDS</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">    <span class="o">.</span><span class="na">every</span><span class="o">(</span><span class="n">Time</span><span class="o">.</span><span class="na">of</span><span class="o">(</span><span class="mi">5</span><span class="o">,</span> <span class="n">TimeUnit</span><span class="o">.</span><span class="na">SECONDS</span><span class="o">));</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Compute some simple statistics on a rolling window
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="n">DataStream</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">lowest</span> <span class="o">=</span> <span class="n">windowedStream</span><span class="o">.</span><span class="na">minBy</span><span class="o">(</span><span class="s">&#34;price&#34;</span><span class="o">).</span><span class="na">flatten</span><span class="o">();</span>
 </span></span><span class="line"><span class="cl"><span class="n">DataStream</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">maxByStock</span> <span class="o">=</span> <span class="n">windowedStream</span><span class="o">.</span><span class="na">groupBy</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">    <span class="o">.</span><span class="na">maxBy</span><span class="o">(</span><span class="s">&#34;price&#34;</span><span class="o">).</span><span class="na">flatten</span><span class="o">();</span>
 </span></span><span class="line"><span class="cl"><span class="n">DataStream</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">rollingMean</span> <span class="o">=</span> <span class="n">windowedStream</span><span class="o">.</span><span class="na">groupBy</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">    <span class="o">.</span><span class="na">mapWindow</span><span class="o">(</span><span class="k">new</span> <span class="n">WindowMean</span><span class="o">()).</span><span class="na">flatten</span><span class="o">();</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Compute the mean of a window
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="kd">public</span> <span class="kd">final</span> <span class="kd">static</span> <span class="kd">class</span> <span class="nc">WindowMean</span> <span class="kd">implements</span>
 </span></span><span class="line"><span class="cl">    <span class="n">WindowMapFunction</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">,</span> <span class="n">StockPrice</span><span class="o">&gt;</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">Double</span> <span class="n">sum</span> <span class="o">=</span> <span class="mf">0.0</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">Integer</span> <span class="n">count</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">String</span> <span class="n">symbol</span> <span class="o">=</span> <span class="s">&#34;&#34;</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kt">void</span> <span class="nf">mapWindow</span><span class="o">(</span><span class="n">Iterable</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">values</span><span class="o">,</span> <span class="n">Collector</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">out</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">        <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">        <span class="k">if</span> <span class="o">(</span><span class="n">values</span><span class="o">.</span><span class="na">iterator</span><span class="o">().</span><span class="na">hasNext</span><span class="o">())</span> <span class="o">{</span><span class="n">s</span>
 </span></span><span class="line"><span class="cl">            <span class="nf">for</span> <span class="o">(</span><span class="n">StockPrice</span> <span class="n">sp</span> <span class="o">:</span> <span class="n">values</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">                <span class="n">sum</span> <span class="o">+=</span> <span class="n">sp</span><span class="o">.</span><span class="na">price</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">                <span class="n">symbol</span> <span class="o">=</span> <span class="n">sp</span><span class="o">.</span><span class="na">symbol</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">                <span class="n">count</span><span class="o">++;</span>
 </span></span><span class="line"><span class="cl">            <span class="o">}</span>
 </span></span><span class="line"><span class="cl">            <span class="n">out</span><span class="o">.</span><span class="na">collect</span><span class="o">(</span><span class="k">new</span> <span class="n">StockPrice</span><span class="o">(</span><span class="n">symbol</span><span class="o">,</span> <span class="n">sum</span> <span class="o">/</span> <span class="n">count</span><span class="o">));</span>
 </span></span><span class="line"><span class="cl">        <span class="o">}</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span></span></span></code></pre></div>
 </div>
 </div>
 <p>Let us note that to print a windowed stream one has to flatten it first,
 thus getting rid of the windowing logic. For example execute
 <code>maxByStock.flatten().print()</code> to print the stream of maximum prices of
 the time windows by stock. For Scala <code>flatten()</code> is called implicitly
 when needed.</p>
 <p><a href="#top">Back to top</a></p>
 <h2 id="data-driven-windows">
   Data-driven windows
   <a class="anchor" href="#data-driven-windows">#</a>
 </h2>
 <p>The most interesting event in the stream is when the price of a stock
 is changing rapidly. We can send a warning when a stock price changes
 more than 5% since the last warning. To do that, we use a delta-based window providing a
 threshold on when the computation will be triggered, a function to
 compute the difference and a default value with which the first record
 is compared. We also create a <code>Count</code> data type to count the warnings
 every 30 seconds.</p>
 <img alt="Data-driven windowing semantics" src="/img/blog/blog_data_driven.png" width="100%" class="img-responsive center-block">
 <div class="codetabs" markdown="1">
 <div data-lang="scala" markdown="1">
 <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-scala" data-lang="scala"><span class="line"><span class="cl"><span class="k">case</span> <span class="k">class</span> <span class="nc">Count</span><span class="o">(</span><span class="n">symbol</span><span class="k">:</span> <span class="kt">String</span><span class="o">,</span> <span class="n">count</span><span class="k">:</span> <span class="kt">Int</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl"><span class="k">val</span> <span class="n">defaultPrice</span> <span class="k">=</span> <span class="nc">StockPrice</span><span class="o">(</span><span class="s">&#34;&#34;</span><span class="o">,</span> <span class="mi">1000</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Use delta policy to create price change warnings
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="k">val</span> <span class="n">priceWarnings</span> <span class="k">=</span> <span class="n">stockStream</span><span class="o">.</span><span class="n">groupBy</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">window</span><span class="o">(</span><span class="nc">Delta</span><span class="o">.</span><span class="n">of</span><span class="o">(</span><span class="mf">0.05</span><span class="o">,</span> <span class="n">priceChange</span><span class="o">,</span> <span class="n">defaultPrice</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">mapWindow</span><span class="o">(</span><span class="n">sendWarning</span> <span class="k">_</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Count the number of warnings every half a minute
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="k">val</span> <span class="n">warningsPerStock</span> <span class="k">=</span> <span class="n">priceWarnings</span><span class="o">.</span><span class="n">map</span><span class="o">(</span><span class="nc">Count</span><span class="o">(</span><span class="k">_</span><span class="o">,</span> <span class="mi">1</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">groupBy</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">window</span><span class="o">(</span><span class="nc">Time</span><span class="o">.</span><span class="n">of</span><span class="o">(</span><span class="mi">30</span><span class="o">,</span> <span class="nc">SECONDS</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">sum</span><span class="o">(</span><span class="s">&#34;count&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="k">def</span> <span class="n">priceChange</span><span class="o">(</span><span class="n">p1</span><span class="k">:</span> <span class="kt">StockPrice</span><span class="o">,</span> <span class="n">p2</span><span class="k">:</span> <span class="kt">StockPrice</span><span class="o">)</span><span class="k">:</span> <span class="kt">Double</span> <span class="o">=</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">  <span class="nc">Math</span><span class="o">.</span><span class="n">abs</span><span class="o">(</span><span class="n">p1</span><span class="o">.</span><span class="n">price</span> <span class="o">/</span> <span class="n">p2</span><span class="o">.</span><span class="n">price</span> <span class="o">-</span> <span class="mi">1</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="k">def</span> <span class="n">sendWarning</span><span class="o">(</span><span class="n">ts</span><span class="k">:</span> <span class="kt">Iterable</span><span class="o">[</span><span class="kt">StockPrice</span><span class="o">],</span> <span class="n">out</span><span class="k">:</span> <span class="kt">Collector</span><span class="o">[</span><span class="kt">String</span><span class="o">])</span> <span class="k">=</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">  <span class="k">if</span> <span class="o">(</span><span class="n">ts</span><span class="o">.</span><span class="n">nonEmpty</span><span class="o">)</span> <span class="n">out</span><span class="o">.</span><span class="n">collect</span><span class="o">(</span><span class="n">ts</span><span class="o">.</span><span class="n">head</span><span class="o">.</span><span class="n">symbol</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span></span></span></code></pre></div>
 </div>
 <div data-lang="java7" markdown="1">
 <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">Double</span> <span class="n">DEFAULT_PRICE</span> <span class="o">=</span> <span class="mf">1000.</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl"><span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">StockPrice</span> <span class="n">DEFAULT_STOCK_PRICE</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StockPrice</span><span class="o">(</span><span class="s">&#34;&#34;</span><span class="o">,</span> <span class="n">DEFAULT_PRICE</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Use delta policy to create price change warnings
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="n">DataStream</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="n">priceWarnings</span> <span class="o">=</span> <span class="n">stockStream</span><span class="o">.</span><span class="na">groupBy</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">    <span class="o">.</span><span class="na">window</span><span class="o">(</span><span class="n">Delta</span><span class="o">.</span><span class="na">of</span><span class="o">(</span><span class="mf">0.05</span><span class="o">,</span> <span class="k">new</span> <span class="n">DeltaFunction</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;()</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">        <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">        <span class="kd">public</span> <span class="kt">double</span> <span class="nf">getDelta</span><span class="o">(</span><span class="n">StockPrice</span> <span class="n">oldDataPoint</span><span class="o">,</span> <span class="n">StockPrice</span> <span class="n">newDataPoint</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">            <span class="k">return</span> <span class="n">Math</span><span class="o">.</span><span class="na">abs</span><span class="o">(</span><span class="n">oldDataPoint</span><span class="o">.</span><span class="na">price</span> <span class="o">-</span> <span class="n">newDataPoint</span><span class="o">.</span><span class="na">price</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">        <span class="o">}</span>
 </span></span><span class="line"><span class="cl">    <span class="o">},</span> <span class="n">DEFAULT_STOCK_PRICE</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl"><span class="o">.</span><span class="na">mapWindow</span><span class="o">(</span><span class="k">new</span> <span class="n">SendWarning</span><span class="o">()).</span><span class="na">flatten</span><span class="o">();</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Count the number of warnings every half a minute
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="n">DataStream</span><span class="o">&lt;</span><span class="n">Count</span><span class="o">&gt;</span> <span class="n">warningsPerStock</span> <span class="o">=</span> <span class="n">priceWarnings</span><span class="o">.</span><span class="na">map</span><span class="o">(</span><span class="k">new</span> <span class="n">MapFunction</span><span class="o">&lt;</span><span class="n">String</span><span class="o">,</span> <span class="n">Count</span><span class="o">&gt;()</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="n">Count</span> <span class="nf">map</span><span class="o">(</span><span class="n">String</span> <span class="n">value</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">        <span class="k">return</span> <span class="k">new</span> <span class="n">Count</span><span class="o">(</span><span class="n">value</span><span class="o">,</span> <span class="mi">1</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}).</span><span class="na">groupBy</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">).</span><span class="na">window</span><span class="o">(</span><span class="n">Time</span><span class="o">.</span><span class="na">of</span><span class="o">(</span><span class="mi">30</span><span class="o">,</span> <span class="n">TimeUnit</span><span class="o">.</span><span class="na">SECONDS</span><span class="o">)).</span><span class="na">sum</span><span class="o">(</span><span class="s">&#34;count&#34;</span><span class="o">).</span><span class="na">flatten</span><span class="o">();</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">static</span> <span class="kd">class</span> <span class="nc">Count</span> <span class="kd">implements</span> <span class="n">Serializable</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="n">String</span> <span class="n">symbol</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="n">Integer</span> <span class="n">count</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="nf">Count</span><span class="o">()</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="nf">Count</span><span class="o">(</span><span class="n">String</span> <span class="n">symbol</span><span class="o">,</span> <span class="n">Integer</span> <span class="n">count</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">        <span class="k">this</span><span class="o">.</span><span class="na">symbol</span> <span class="o">=</span> <span class="n">symbol</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">        <span class="k">this</span><span class="o">.</span><span class="na">count</span> <span class="o">=</span> <span class="n">count</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="n">String</span> <span class="nf">toString</span><span class="o">()</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">        <span class="k">return</span> <span class="s">&#34;Count{&#34;</span> <span class="o">+</span>
 </span></span><span class="line"><span class="cl">                <span class="s">&#34;symbol=&#39;&#34;</span> <span class="o">+</span> <span class="n">symbol</span> <span class="o">+</span> <span class="sc">&#39;\&#39;&#39;</span> <span class="o">+</span>
 </span></span><span class="line"><span class="cl">                <span class="s">&#34;, count=&#34;</span> <span class="o">+</span> <span class="n">count</span> <span class="o">+</span>
 </span></span><span class="line"><span class="cl">                <span class="sc">&#39;}&#39;</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">static</span> <span class="kd">final</span> <span class="kd">class</span> <span class="nc">SendWarning</span> <span class="kd">implements</span> <span class="n">MapWindowFunction</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">,</span> <span class="n">String</span><span class="o">&gt;</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kt">void</span> <span class="nf">mapWindow</span><span class="o">(</span><span class="n">Iterable</span><span class="o">&lt;</span><span class="n">StockPrice</span><span class="o">&gt;</span> <span class="n">values</span><span class="o">,</span> <span class="n">Collector</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="n">out</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">        <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">        <span class="k">if</span> <span class="o">(</span><span class="n">values</span><span class="o">.</span><span class="na">iterator</span><span class="o">().</span><span class="na">hasNext</span><span class="o">())</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">            <span class="n">out</span><span class="o">.</span><span class="na">collect</span><span class="o">(</span><span class="n">values</span><span class="o">.</span><span class="na">iterator</span><span class="o">().</span><span class="na">next</span><span class="o">().</span><span class="na">symbol</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">        <span class="o">}</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span></span></span></code></pre></div>
 </div>
 </div>
 <p><a href="#top">Back to top</a></p>
 <h2 id="combining-with-a-twitter-stream">
   Combining with a Twitter stream
   <a class="anchor" href="#combining-with-a-twitter-stream">#</a>
 </h2>
 <p>Next, we will read a Twitter stream and correlate it with our stock
 price stream. Flink has support for connecting to <a href="//nightlies.apache.org/flinkflink-docs-master/apis/streaming/connectors/twitter.html">Twitter&rsquo;s
 API</a>
 but for the sake of this example we generate dummy tweet data.</p>
 <img alt="Social media analytics" src="/img/blog/blog_social_media.png" width="100%" class="img-responsive center-block">
 <div class="codetabs" markdown="1">
 <div data-lang="scala" markdown="1">
 <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-scala" data-lang="scala"><span class="line"><span class="cl"><span class="c1">//Read a stream of tweets
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="k">val</span> <span class="n">tweetStream</span> <span class="k">=</span> <span class="n">env</span><span class="o">.</span><span class="n">addSource</span><span class="o">(</span><span class="n">generateTweets</span> <span class="k">_</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Extract the stock symbols
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="k">val</span> <span class="n">mentionedSymbols</span> <span class="k">=</span> <span class="n">tweetStream</span><span class="o">.</span><span class="n">flatMap</span><span class="o">(</span><span class="n">tweet</span> <span class="k">=&gt;</span> <span class="n">tweet</span><span class="o">.</span><span class="n">split</span><span class="o">(</span><span class="s">&#34; &#34;</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">map</span><span class="o">(</span><span class="k">_</span><span class="o">.</span><span class="n">toUpperCase</span><span class="o">())</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">filter</span><span class="o">(</span><span class="n">symbols</span><span class="o">.</span><span class="n">contains</span><span class="o">(</span><span class="k">_</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Count the extracted symbols
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="k">val</span> <span class="n">tweetsPerStock</span> <span class="k">=</span> <span class="n">mentionedSymbols</span><span class="o">.</span><span class="n">map</span><span class="o">(</span><span class="nc">Count</span><span class="o">(</span><span class="k">_</span><span class="o">,</span> <span class="mi">1</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">groupBy</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">window</span><span class="o">(</span><span class="nc">Time</span><span class="o">.</span><span class="n">of</span><span class="o">(</span><span class="mi">30</span><span class="o">,</span> <span class="nc">SECONDS</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">sum</span><span class="o">(</span><span class="s">&#34;count&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="k">def</span> <span class="n">generateTweets</span><span class="o">(</span><span class="n">out</span><span class="k">:</span> <span class="kt">Collector</span><span class="o">[</span><span class="kt">String</span><span class="o">])</span> <span class="k">=</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">  <span class="k">while</span> <span class="o">(</span><span class="kc">true</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="k">val</span> <span class="n">s</span> <span class="k">=</span> <span class="k">for</span> <span class="o">(</span><span class="n">i</span> <span class="k">&lt;-</span> <span class="mi">1</span> <span class="n">to</span> <span class="mi">3</span><span class="o">)</span> <span class="k">yield</span> <span class="o">(</span><span class="n">symbols</span><span class="o">(</span><span class="nc">Random</span><span class="o">.</span><span class="n">nextInt</span><span class="o">(</span><span class="n">symbols</span><span class="o">.</span><span class="n">size</span><span class="o">)))</span>
 </span></span><span class="line"><span class="cl">    <span class="n">out</span><span class="o">.</span><span class="n">collect</span><span class="o">(</span><span class="n">s</span><span class="o">.</span><span class="n">mkString</span><span class="o">(</span><span class="s">&#34; &#34;</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">    <span class="nc">Thread</span><span class="o">.</span><span class="n">sleep</span><span class="o">(</span><span class="nc">Random</span><span class="o">.</span><span class="n">nextInt</span><span class="o">(</span><span class="mi">500</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">  <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span></span></span></code></pre></div>
 </div>
 <div data-lang="java7" markdown="1">
 <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="c1">//Read a stream of tweets
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="n">DataStream</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="n">tweetStream</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="na">addSource</span><span class="o">(</span><span class="k">new</span> <span class="n">TweetSource</span><span class="o">());</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Extract the stock symbols
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="n">DataStream</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="n">mentionedSymbols</span> <span class="o">=</span> <span class="n">tweetStream</span><span class="o">.</span><span class="na">flatMap</span><span class="o">(</span>
 </span></span><span class="line"><span class="cl">    <span class="k">new</span> <span class="n">FlatMapFunction</span><span class="o">&lt;</span><span class="n">String</span><span class="o">,</span> <span class="n">String</span><span class="o">&gt;()</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kt">void</span> <span class="nf">flatMap</span><span class="o">(</span><span class="n">String</span> <span class="n">value</span><span class="o">,</span> <span class="n">Collector</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="n">out</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">        <span class="n">String</span><span class="o">[]</span> <span class="n">words</span> <span class="o">=</span> <span class="n">value</span><span class="o">.</span><span class="na">split</span><span class="o">(</span><span class="s">&#34; &#34;</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">        <span class="k">for</span> <span class="o">(</span><span class="n">String</span> <span class="n">word</span> <span class="o">:</span> <span class="n">words</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">            <span class="n">out</span><span class="o">.</span><span class="na">collect</span><span class="o">(</span><span class="n">word</span><span class="o">.</span><span class="na">toUpperCase</span><span class="o">());</span>
 </span></span><span class="line"><span class="cl">        <span class="o">}</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}).</span><span class="na">filter</span><span class="o">(</span><span class="k">new</span> <span class="n">FilterFunction</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;()</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kt">boolean</span> <span class="nf">filter</span><span class="o">(</span><span class="n">String</span> <span class="n">value</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">        <span class="k">return</span> <span class="n">SYMBOLS</span><span class="o">.</span><span class="na">contains</span><span class="o">(</span><span class="n">value</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">});</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Count the extracted symbols
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="n">DataStream</span><span class="o">&lt;</span><span class="n">Count</span><span class="o">&gt;</span> <span class="n">tweetsPerStock</span> <span class="o">=</span> <span class="n">mentionedSymbols</span><span class="o">.</span><span class="na">map</span><span class="o">(</span><span class="k">new</span> <span class="n">MapFunction</span><span class="o">&lt;</span><span class="n">String</span><span class="o">,</span> <span class="n">Count</span><span class="o">&gt;()</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="n">Count</span> <span class="nf">map</span><span class="o">(</span><span class="n">String</span> <span class="n">value</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">        <span class="k">return</span> <span class="k">new</span> <span class="n">Count</span><span class="o">(</span><span class="n">value</span><span class="o">,</span> <span class="mi">1</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}).</span><span class="na">groupBy</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">).</span><span class="na">window</span><span class="o">(</span><span class="n">Time</span><span class="o">.</span><span class="na">of</span><span class="o">(</span><span class="mi">30</span><span class="o">,</span> <span class="n">TimeUnit</span><span class="o">.</span><span class="na">SECONDS</span><span class="o">)).</span><span class="na">sum</span><span class="o">(</span><span class="s">&#34;count&#34;</span><span class="o">).</span><span class="na">flatten</span><span class="o">();</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">static</span> <span class="kd">final</span> <span class="kd">class</span> <span class="nc">TweetSource</span> <span class="kd">implements</span> <span class="n">SourceFunction</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="n">Random</span> <span class="n">random</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="n">StringBuilder</span> <span class="n">stringBuilder</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kt">void</span> <span class="nf">invoke</span><span class="o">(</span><span class="n">Collector</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="n">collector</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">        <span class="n">random</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Random</span><span class="o">();</span>
 </span></span><span class="line"><span class="cl">        <span class="n">stringBuilder</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StringBuilder</span><span class="o">();</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">        <span class="k">while</span> <span class="o">(</span><span class="kc">true</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">            <span class="n">stringBuilder</span><span class="o">.</span><span class="na">setLength</span><span class="o">(</span><span class="mi">0</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">            <span class="k">for</span> <span class="o">(</span><span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span> <span class="n">i</span> <span class="o">&lt;</span> <span class="mi">3</span><span class="o">;</span> <span class="n">i</span><span class="o">++)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">                <span class="n">stringBuilder</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="s">&#34; &#34;</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">                <span class="n">stringBuilder</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="n">SYMBOLS</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="n">random</span><span class="o">.</span><span class="na">nextInt</span><span class="o">(</span><span class="n">SYMBOLS</span><span class="o">.</span><span class="na">size</span><span class="o">())));</span>
 </span></span><span class="line"><span class="cl">            <span class="o">}</span>
 </span></span><span class="line"><span class="cl">            <span class="n">collector</span><span class="o">.</span><span class="na">collect</span><span class="o">(</span><span class="n">stringBuilder</span><span class="o">.</span><span class="na">toString</span><span class="o">());</span>
 </span></span><span class="line"><span class="cl">            <span class="n">Thread</span><span class="o">.</span><span class="na">sleep</span><span class="o">(</span><span class="mi">500</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">        <span class="o">}</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span></span></span></code></pre></div>
 </div>
 </div>
 <p><a href="#top">Back to top</a></p>
 <h2 id="streaming-joins">
   Streaming joins
   <a class="anchor" href="#streaming-joins">#</a>
 </h2>
 <p>Finally, we join real-time tweets and stock prices and compute a
 rolling correlation between the number of price warnings and the
 number of mentions of a given stock in the Twitter stream. As both of
 these data streams are potentially infinite, we apply the join on a
 30-second window.</p>
 <img alt="Streaming joins" src="/img/blog/blog_stream_join.png" width="60%" class="img-responsive center-block">
 <div class="codetabs" markdown="1">
 <div data-lang="scala" markdown="1">
 <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-scala" data-lang="scala"><span class="line"><span class="cl"><span class="c1">//Join warnings and parsed tweets
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="k">val</span> <span class="n">tweetsAndWarning</span> <span class="k">=</span> <span class="n">warningsPerStock</span><span class="o">.</span><span class="n">join</span><span class="o">(</span><span class="n">tweetsPerStock</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">onWindow</span><span class="o">(</span><span class="mi">30</span><span class="o">,</span> <span class="nc">SECONDS</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">where</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">equalTo</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">)</span> <span class="o">{</span> <span class="o">(</span><span class="n">c1</span><span class="o">,</span> <span class="n">c2</span><span class="o">)</span> <span class="k">=&gt;</span> <span class="o">(</span><span class="n">c1</span><span class="o">.</span><span class="n">count</span><span class="o">,</span> <span class="n">c2</span><span class="o">.</span><span class="n">count</span><span class="o">)</span> <span class="o">}</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="k">val</span> <span class="n">rollingCorrelation</span> <span class="k">=</span> <span class="n">tweetsAndWarning</span><span class="o">.</span><span class="n">window</span><span class="o">(</span><span class="nc">Time</span><span class="o">.</span><span class="n">of</span><span class="o">(</span><span class="mi">30</span><span class="o">,</span> <span class="nc">SECONDS</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">  <span class="o">.</span><span class="n">mapWindow</span><span class="o">(</span><span class="n">computeCorrelation</span> <span class="k">_</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="n">rollingCorrelation</span> <span class="n">print</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Compute rolling correlation
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="k">def</span> <span class="n">computeCorrelation</span><span class="o">(</span><span class="n">input</span><span class="k">:</span> <span class="kt">Iterable</span><span class="o">[(</span><span class="kt">Int</span>, <span class="kt">Int</span><span class="o">)],</span> <span class="n">out</span><span class="k">:</span> <span class="kt">Collector</span><span class="o">[</span><span class="kt">Double</span><span class="o">])</span> <span class="k">=</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">  <span class="k">if</span> <span class="o">(</span><span class="n">input</span><span class="o">.</span><span class="n">nonEmpty</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">    <span class="k">val</span> <span class="n">var1</span> <span class="k">=</span> <span class="n">input</span><span class="o">.</span><span class="n">map</span><span class="o">(</span><span class="k">_</span><span class="o">.</span><span class="n">_1</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">    <span class="k">val</span> <span class="n">mean1</span> <span class="k">=</span> <span class="n">average</span><span class="o">(</span><span class="n">var1</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">    <span class="k">val</span> <span class="n">var2</span> <span class="k">=</span> <span class="n">input</span><span class="o">.</span><span class="n">map</span><span class="o">(</span><span class="k">_</span><span class="o">.</span><span class="n">_2</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">    <span class="k">val</span> <span class="n">mean2</span> <span class="k">=</span> <span class="n">average</span><span class="o">(</span><span class="n">var2</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="k">val</span> <span class="n">cov</span> <span class="k">=</span> <span class="n">average</span><span class="o">(</span><span class="n">var1</span><span class="o">.</span><span class="n">zip</span><span class="o">(</span><span class="n">var2</span><span class="o">).</span><span class="n">map</span><span class="o">(</span><span class="n">xy</span> <span class="k">=&gt;</span> <span class="o">(</span><span class="n">xy</span><span class="o">.</span><span class="n">_1</span> <span class="o">-</span> <span class="n">mean1</span><span class="o">)</span> <span class="o">*</span> <span class="o">(</span><span class="n">xy</span><span class="o">.</span><span class="n">_2</span> <span class="o">-</span> <span class="n">mean2</span><span class="o">)))</span>
 </span></span><span class="line"><span class="cl">    <span class="k">val</span> <span class="n">d1</span> <span class="k">=</span> <span class="nc">Math</span><span class="o">.</span><span class="n">sqrt</span><span class="o">(</span><span class="n">average</span><span class="o">(</span><span class="n">var1</span><span class="o">.</span><span class="n">map</span><span class="o">(</span><span class="n">x</span> <span class="k">=&gt;</span> <span class="nc">Math</span><span class="o">.</span><span class="n">pow</span><span class="o">((</span><span class="n">x</span> <span class="o">-</span> <span class="n">mean1</span><span class="o">),</span> <span class="mi">2</span><span class="o">))))</span>
 </span></span><span class="line"><span class="cl">    <span class="k">val</span> <span class="n">d2</span> <span class="k">=</span> <span class="nc">Math</span><span class="o">.</span><span class="n">sqrt</span><span class="o">(</span><span class="n">average</span><span class="o">(</span><span class="n">var2</span><span class="o">.</span><span class="n">map</span><span class="o">(</span><span class="n">x</span> <span class="k">=&gt;</span> <span class="nc">Math</span><span class="o">.</span><span class="n">pow</span><span class="o">((</span><span class="n">x</span> <span class="o">-</span> <span class="n">mean2</span><span class="o">),</span> <span class="mi">2</span><span class="o">))))</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="n">out</span><span class="o">.</span><span class="n">collect</span><span class="o">(</span><span class="n">cov</span> <span class="o">/</span> <span class="o">(</span><span class="n">d1</span> <span class="o">*</span> <span class="n">d2</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">  <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span></span></span></code></pre></div>
 </div>
 <div data-lang="java7" markdown="1">
 <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="c1">//Join warnings and parsed tweets
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="n">DataStream</span><span class="o">&lt;</span><span class="n">Tuple2</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">,</span> <span class="n">Integer</span><span class="o">&gt;&gt;</span> <span class="n">tweetsAndWarning</span> <span class="o">=</span> <span class="n">warningsPerStock</span>
 </span></span><span class="line"><span class="cl">    <span class="o">.</span><span class="na">join</span><span class="o">(</span><span class="n">tweetsPerStock</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">    <span class="o">.</span><span class="na">onWindow</span><span class="o">(</span><span class="mi">30</span><span class="o">,</span> <span class="n">TimeUnit</span><span class="o">.</span><span class="na">SECONDS</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">    <span class="o">.</span><span class="na">where</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">    <span class="o">.</span><span class="na">equalTo</span><span class="o">(</span><span class="s">&#34;symbol&#34;</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">    <span class="o">.</span><span class="na">with</span><span class="o">(</span><span class="k">new</span> <span class="n">JoinFunction</span><span class="o">&lt;</span><span class="n">Count</span><span class="o">,</span> <span class="n">Count</span><span class="o">,</span> <span class="n">Tuple2</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">,</span> <span class="n">Integer</span><span class="o">&gt;&gt;()</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">        <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">        <span class="kd">public</span> <span class="n">Tuple2</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">,</span> <span class="n">Integer</span><span class="o">&gt;</span> <span class="nf">join</span><span class="o">(</span><span class="n">Count</span> <span class="n">first</span><span class="o">,</span> <span class="n">Count</span> <span class="n">second</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">            <span class="k">return</span> <span class="k">new</span> <span class="n">Tuple2</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">,</span> <span class="n">Integer</span><span class="o">&gt;(</span><span class="n">first</span><span class="o">.</span><span class="na">count</span><span class="o">,</span> <span class="n">second</span><span class="o">.</span><span class="na">count</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">            <span class="o">}</span>
 </span></span><span class="line"><span class="cl">    <span class="o">});</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="c1">//Compute rolling correlation
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="n">DataStream</span><span class="o">&lt;</span><span class="n">Double</span><span class="o">&gt;</span> <span class="n">rollingCorrelation</span> <span class="o">=</span> <span class="n">tweetsAndWarning</span>
 </span></span><span class="line"><span class="cl">    <span class="o">.</span><span class="na">window</span><span class="o">(</span><span class="n">Time</span><span class="o">.</span><span class="na">of</span><span class="o">(</span><span class="mi">30</span><span class="o">,</span> <span class="n">TimeUnit</span><span class="o">.</span><span class="na">SECONDS</span><span class="o">))</span>
 </span></span><span class="line"><span class="cl">    <span class="o">.</span><span class="na">mapWindow</span><span class="o">(</span><span class="k">new</span> <span class="n">WindowCorrelation</span><span class="o">());</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="n">rollingCorrelation</span><span class="o">.</span><span class="na">print</span><span class="o">();</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">static</span> <span class="kd">final</span> <span class="kd">class</span> <span class="nc">WindowCorrelation</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">implements</span> <span class="n">WindowMapFunction</span><span class="o">&lt;</span><span class="n">Tuple2</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">,</span> <span class="n">Integer</span><span class="o">&gt;,</span> <span class="n">Double</span><span class="o">&gt;</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">Integer</span> <span class="n">leftSum</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">Integer</span> <span class="n">rightSum</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">Integer</span> <span class="n">count</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">Double</span> <span class="n">leftMean</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">Double</span> <span class="n">rightMean</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">Double</span> <span class="n">cov</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">Double</span> <span class="n">leftSd</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">Double</span> <span class="n">rightSd</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
 </span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kt">void</span> <span class="nf">mapWindow</span><span class="o">(</span><span class="n">Iterable</span><span class="o">&lt;</span><span class="n">Tuple2</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">,</span> <span class="n">Integer</span><span class="o">&gt;&gt;</span> <span class="n">values</span><span class="o">,</span> <span class="n">Collector</span><span class="o">&lt;</span><span class="n">Double</span><span class="o">&gt;</span> <span class="n">out</span><span class="o">)</span>
 </span></span><span class="line"><span class="cl">        <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">        <span class="n">leftSum</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">        <span class="n">rightSum</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">        <span class="n">count</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">        <span class="n">cov</span> <span class="o">=</span> <span class="mf">0.</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">        <span class="n">leftSd</span> <span class="o">=</span> <span class="mf">0.</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">        <span class="n">rightSd</span> <span class="o">=</span> <span class="mf">0.</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">        <span class="c1">//compute mean for both sides, save count
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="k">for</span> <span class="o">(</span><span class="n">Tuple2</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">,</span> <span class="n">Integer</span><span class="o">&gt;</span> <span class="n">pair</span> <span class="o">:</span> <span class="n">values</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">            <span class="n">leftSum</span> <span class="o">+=</span> <span class="n">pair</span><span class="o">.</span><span class="na">f0</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">            <span class="n">rightSum</span> <span class="o">+=</span> <span class="n">pair</span><span class="o">.</span><span class="na">f1</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">            <span class="n">count</span><span class="o">++;</span>
 </span></span><span class="line"><span class="cl">        <span class="o">}</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">        <span class="n">leftMean</span> <span class="o">=</span> <span class="n">leftSum</span><span class="o">.</span><span class="na">doubleValue</span><span class="o">()</span> <span class="o">/</span> <span class="n">count</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">        <span class="n">rightMean</span> <span class="o">=</span> <span class="n">rightSum</span><span class="o">.</span><span class="na">doubleValue</span><span class="o">()</span> <span class="o">/</span> <span class="n">count</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">        <span class="c1">//compute covariance &amp; std. deviations
 </span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="k">for</span> <span class="o">(</span><span class="n">Tuple2</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">,</span> <span class="n">Integer</span><span class="o">&gt;</span> <span class="n">pair</span> <span class="o">:</span> <span class="n">values</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">            <span class="n">cov</span> <span class="o">+=</span> <span class="o">(</span><span class="n">pair</span><span class="o">.</span><span class="na">f0</span> <span class="o">-</span> <span class="n">leftMean</span><span class="o">)</span> <span class="o">*</span> <span class="o">(</span><span class="n">pair</span><span class="o">.</span><span class="na">f1</span> <span class="o">-</span> <span class="n">rightMean</span><span class="o">)</span> <span class="o">/</span> <span class="n">count</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">        <span class="o">}</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">        <span class="k">for</span> <span class="o">(</span><span class="n">Tuple2</span><span class="o">&lt;</span><span class="n">Integer</span><span class="o">,</span> <span class="n">Integer</span><span class="o">&gt;</span> <span class="n">pair</span> <span class="o">:</span> <span class="n">values</span><span class="o">)</span> <span class="o">{</span>
 </span></span><span class="line"><span class="cl">            <span class="n">leftSd</span> <span class="o">+=</span> <span class="n">Math</span><span class="o">.</span><span class="na">pow</span><span class="o">(</span><span class="n">pair</span><span class="o">.</span><span class="na">f0</span> <span class="o">-</span> <span class="n">leftMean</span><span class="o">,</span> <span class="mi">2</span><span class="o">)</span> <span class="o">/</span> <span class="n">count</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">            <span class="n">rightSd</span> <span class="o">+=</span> <span class="n">Math</span><span class="o">.</span><span class="na">pow</span><span class="o">(</span><span class="n">pair</span><span class="o">.</span><span class="na">f1</span> <span class="o">-</span> <span class="n">rightMean</span><span class="o">,</span> <span class="mi">2</span><span class="o">)</span> <span class="o">/</span> <span class="n">count</span><span class="o">;</span>
 </span></span><span class="line"><span class="cl">        <span class="o">}</span>
 </span></span><span class="line"><span class="cl">        <span class="n">leftSd</span> <span class="o">=</span> <span class="n">Math</span><span class="o">.</span><span class="na">sqrt</span><span class="o">(</span><span class="n">leftSd</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">        <span class="n">rightSd</span> <span class="o">=</span> <span class="n">Math</span><span class="o">.</span><span class="na">sqrt</span><span class="o">(</span><span class="n">rightSd</span><span class="o">);</span>
 </span></span><span class="line"><span class="cl">
 </span></span><span class="line"><span class="cl">        <span class="n">out</span><span class="o">.</span><span class="na">collect</span><span class="o">(</span><span class="n">cov</span> <span class="o">/</span> <span class="o">(</span><span class="n">leftSd</span> <span class="o">*</span> <span class="n">rightSd</span><span class="o">));</span>
 </span></span><span class="line"><span class="cl">    <span class="o">}</span>
 </span></span><span class="line"><span class="cl"><span class="o">}</span></span></span></code></pre></div>
 </div>
 </div>
 <p><a href="#top">Back to top</a></p>
 <h2 id="other-things-to-try">
   Other things to try
   <a class="anchor" href="#other-things-to-try">#</a>
 </h2>
 <p>For a full feature overview please check the <a href="//nightlies.apache.org/flinkflink-docs-master/apis/streaming/index.html">Streaming Guide</a>, which describes all the available API features.
 You are very welcome to try out our features for different use-cases we are looking forward to your experiences. Feel free to <a href="http://flink.apache.org/community.html#mailing-lists">contact us</a>.</p>
 <h2 id="upcoming-for-streaming">
   Upcoming for streaming
   <a class="anchor" href="#upcoming-for-streaming">#</a>
 </h2>
 <p>There are some aspects of Flink Streaming that are subjects to
 change by the next release making this application look even nicer.</p>
 <p>Stay tuned for later blog posts on how Flink Streaming works
 internally, fault tolerance, and performance measurements!</p>
 <p><a href="#top">Back to top</a></p>
 </p>
 </article>


       <footer class="book-footer">


 <a href="https://cwiki.apache.org/confluence/display/FLINK/Flink+Translation+Specifications">Want to contribute translation?</a>
 <br><br>
 <a href="//github.com/apache/flink-web/edit/asf-site/docs/content/posts/2015-02-09-streaming-example.md" style="color:black"><i class="fa fa-edit fa-fw"></i>Edit This Page</a>


       </footer>


   <div class="book-comments">

 </div>


       <label for="menu-control" class="hidden book-menu-overlay"></label>
     </div>


     <aside class="book-toc">


 <nav id="TableOfContents"><h3>On This Page <button class="toc" onclick="collapseToc()"><i class="fa fa-compress" aria-hidden="true"></i></button></h3>
   <ul>
     <li><a href="#reading-from-multiple-inputs">Reading from multiple inputs</a></li>
     <li><a href="#window-aggregations">Window aggregations</a></li>
     <li><a href="#data-driven-windows">Data-driven windows</a></li>
     <li><a href="#combining-with-a-twitter-stream">Combining with a Twitter stream</a></li>
     <li><a href="#streaming-joins">Streaming joins</a></li>
     <li><a href="#other-things-to-try">Other things to try</a></li>
     <li><a href="#upcoming-for-streaming">Upcoming for streaming</a></li>
   </ul>
 </nav>


     </aside>
     <aside class="expand-toc">
       <button class="toc" onclick="expandToc()">
         <i class="fa fa-expand" aria-hidden="true"></i>
       </button>
     </aside>

   </main>


 </body>

 </html>