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   <title>Configuring HTTP/2 Push</title><link rel="stylesheet" type="text/css" href="css/docbook.css"><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><meta name="keywords" content="jetty, servlet, servlet-api, cometd, http, websocket, eclipse, maven, java, server, software"><link rel="home" href="index.html" title="Jetty"><link rel="up" href="http2.html" title="Chapter&nbsp;16.&nbsp;HTTP/2"><link rel="prev" href="http2-configuring.html" title="Configuring HTTP/2"><link rel="next" href="http2-configuring-haproxy.html" title="Configuring HAProxy and Jetty"><link xmlns:jfetch="java:org.eclipse.jetty.xslt.tools.JavaSourceFetchExtension" xmlns:fetch="java:org.eclipse.jetty.xslt.tools.SourceFetchExtension" xmlns:d="http://docbook.org/ns/docbook" xmlns:l="http://docbook.sourceforge.net/xmlns/l10n/1.0" xmlns:xslthl="http://xslthl.sf.net" xmlns:gcse="http://www.google.com" xmlns:date="http://exslt.org/dates-and-times" rel="shortcut icon" href="images/favicon.ico"><link rel="stylesheet" href="css/highlighter/foundation.css"><script src="js/highlight.pack.js"></script><script>
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            Version: 9.4.27.v20200227</span></td><td style="width: 50%"></td></tr></table><div xmlns:jfetch="java:org.eclipse.jetty.xslt.tools.JavaSourceFetchExtension" xmlns:fetch="java:org.eclipse.jetty.xslt.tools.SourceFetchExtension" xmlns:d="http://docbook.org/ns/docbook" xmlns:l="http://docbook.sourceforge.net/xmlns/l10n/1.0" xmlns:xslthl="http://xslthl.sf.net" xmlns:gcse="http://www.google.com" xmlns:date="http://exslt.org/dates-and-times" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Configuring HTTP/2 Push</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="http2-configuring.html"><i class="fa fa-chevron-left" aria-hidden="true"></i> Previous</a>&nbsp;</td><th width="60%" align="center">Chapter&nbsp;16.&nbsp;HTTP/2<br><a accesskey="p" href="index.html"><i class="fa fa-home" aria-hidden="true"></i> Home</a></th><td width="20%" align="right">&nbsp;<a accesskey="n" href="http2-configuring-haproxy.html">Next <i class="fa fa-chevron-right" aria-hidden="true"></i></a></td></tr></table><hr></div><div xmlns:jfetch="java:org.eclipse.jetty.xslt.tools.JavaSourceFetchExtension" xmlns:fetch="java:org.eclipse.jetty.xslt.tools.SourceFetchExtension" xmlns:d="http://docbook.org/ns/docbook" xmlns:l="http://docbook.sourceforge.net/xmlns/l10n/1.0" xmlns:xslthl="http://xslthl.sf.net" xmlns:gcse="http://www.google.com" xmlns:date="http://exslt.org/dates-and-times" class="jetty-callout"><h5 class="callout"><a href="http://www.webtide.com/">Contact the core Jetty developers at
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      </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="http2-configuring-push"></a>Configuring HTTP/2 Push</h2></div></div></div><p>HTTP/2 Push is a mechanism that allows the server to send multiple resources to the client for a single client request.
This will reduce the amount of round-trips necessary to retrieve all the resources that make up a web page and can significantly improve the page load time.</p><p>HTTP/2 Push can be automated in your application by configuring a <a class="link" href="http://www.eclipse.org/jetty/javadoc/9.4.27.v20200227/org/eclipse/jetty/servlets/PushCacheFilter.html" target="_top"><code class="literal">PushCacheFilter</code></a> in the <code class="literal">web.xml</code>, in this way:</p><pre xmlns:jfetch="java:org.eclipse.jetty.xslt.tools.JavaSourceFetchExtension" xmlns:fetch="java:org.eclipse.jetty.xslt.tools.SourceFetchExtension" xmlns:d="http://docbook.org/ns/docbook" xmlns:l="http://docbook.sourceforge.net/xmlns/l10n/1.0" xmlns:xslthl="http://xslthl.sf.net" xmlns:gcse="http://www.google.com" xmlns:date="http://exslt.org/dates-and-times"><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;web-app
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
    metadata-complete="true"
    version="3.1"&gt;

    ...
    &lt;filter&gt;
        &lt;filter-name&gt;PushFilter&lt;/filter-name&gt;
        &lt;filter-class&gt;org.eclipse.jetty.servlets.PushCacheFilter&lt;/filter-class&gt;
        &lt;async-supported&gt;true&lt;/async-supported&gt;
    &lt;/filter&gt;
    &lt;filter-mapping&gt;
        &lt;filter-name&gt;PushFilter&lt;/filter-name&gt;
        &lt;url-pattern&gt;/*&lt;/url-pattern&gt;
    &lt;/filter-mapping&gt;
    ...

&lt;/web-app&gt;</code></pre><p><code class="literal">PushCacheFilter</code> analyzes the HTTP requests for resources that arrive to your web application.
Some of these requests contain the HTTP <code class="literal">Referer</code> header that points to a resource that has been requested previously.</p><p>This allows the <code class="literal">PushCacheFilter</code> to organize resources in a tree, for example a root <code class="literal">index.html</code> resource having two children resources, <code class="literal">styles.css</code> and <code class="literal">application.js</code>, and <code class="literal">styles.css</code> having a child resource, <code class="literal">background.png</code>.
The root resource is called the <span class="emphasis"><em>primary</em></span> resource, while descendant resources are called <span class="emphasis"><em>secondary</em></span> resources.</p><p>The resource tree is built using a time window so that when a root resource is requested, only subsequent requests that are made within the time window will be added to the resource tree.
The resource tree can also be limited in size so that the number of secondary resources associated to a primary resource is limited.</p><p>By default, only the resource <span class="emphasis"><em>path</em></span> (without the <span class="emphasis"><em>query</em></span> string) is used to associate secondary resources to the primary resource, but you can configure <code class="literal">PushCacheFilter</code> to take the query string into account.</p><p><code class="literal">PushCacheFilter</code> can be configured with the following <code class="literal">init-params</code>:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="literal">associatePeriod</code>: the time window, in milliseconds, within which a request for a secondary resource will be associated to a primary resource; defaults to 4000 ms</li><li class="listitem"><code class="literal">maxAssociations</code>: the max number of secondary resources that may be associated to a primary resource; defaults to 16</li><li class="listitem"><code class="literal">hosts</code>: a comma separated list of hosts that are allowed in the <code class="literal">Referer</code> header; defaults to the host in the <code class="literal">Host</code> header</li><li class="listitem"><code class="literal">ports</code>: a comma separated list of ports that are allowed in the <code class="literal">Referer</code> header; defaults to the port in the <code class="literal">Host</code> header</li><li class="listitem"><code class="literal">useQueryInKey</code>: a boolean indicating whether the query string of the request should be considered when associating secondary resources to primary resources; defaults to <code class="literal">false</code></li></ul></div></div><script type="text/javascript">
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