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| 2 | <html lang="en"><head><META http-equiv="Content-Type" content="text/html; charset=UTF-8"><link href="../images/docs-stylesheet.css" rel="stylesheet" type="text/css"><title>Apache Tomcat 9 Configuration Reference (9.0.112) - The HTTP2 Upgrade Protocol</title></head><body><div id="wrapper"><header><div id="header"><div><div><div class="logo noPrint"><a href="https://tomcat.apache.org/"><img alt="Tomcat Home" src="../images/tomcat.png"></a></div><div style="height: 1px;"></div><div class="asfLogo noPrint"><a href="https://www.apache.org/" target="_blank"><img src="../images/asf-logo.svg" alt="The Apache Software Foundation" style="width: 266px; height: 83px;"></a></div><h1>Apache Tomcat 9 Configuration Reference</h1><div class="versionInfo"> |
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| 3 | Version 9.0.112, |
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| 4 | <time datetime="2025-11-06">Nov 6 2025</time></div><div style="height: 1px;"></div><div style="clear: left;"></div></div></div></div></header><div id="middle"><div><div id="mainLeft" class="noprint"><div><nav><div><h2>Links</h2><ul><li><a href="../index.html">Docs Home</a></li><li><a href="index.html">Config Ref. Home</a></li><li><a href="https://cwiki.apache.org/confluence/display/TOMCAT/FAQ">FAQ</a></li><li><a href="#comments_section">User Comments</a></li></ul></div><div><h2>Top Level Elements</h2><ul><li><a href="server.html">Server</a></li><li><a href="service.html">Service</a></li></ul></div><div><h2>Executors</h2><ul><li><a href="executor.html">Executor</a></li></ul></div><div><h2>Connectors</h2><ul><li><a href="http.html">HTTP/1.1</a></li><li><a href="http2.html">HTTP/2</a></li><li><a href="ajp.html">AJP</a></li></ul></div><div><h2>Containers</h2><ul><li><a href="context.html">Context</a></li><li><a href="engine.html">Engine</a></li><li><a href="host.html">Host</a></li><li><a href="cluster.html">Cluster</a></li></ul></div><div><h2>Nested Components</h2><ul><li><a href="cookie-processor.html">CookieProcessor</a></li><li><a href="credentialhandler.html">CredentialHandler</a></li><li><a href="globalresources.html">Global Resources</a></li><li><a href="jar-scanner.html">JarScanner</a></li><li><a href="jar-scan-filter.html">JarScanFilter</a></li><li><a href="listeners.html">Listeners</a></li><li><a href="loader.html">Loader</a></li><li><a href="manager.html">Manager</a></li><li><a href="realm.html">Realm</a></li><li><a href="resources.html">Resources</a></li><li><a href="sessionidgenerator.html">SessionIdGenerator</a></li><li><a href="valve.html">Valve</a></li></ul></div><div><h2>Cluster Elements</h2><ul><li><a href="cluster.html">Cluster</a></li><li><a href="cluster-manager.html">Manager</a></li><li><a href="cluster-channel.html">Channel</a></li><li><a href="cluster-membership.html">Channel/Membership</a></li><li><a href="cluster-sender.html">Channel/Sender</a></li><li><a href="cluster-receiver.html">Channel/Receiver</a></li><li><a href="cluster-interceptor.html">Channel/Interceptor</a></li><li><a href="cluster-valve.html">Valve</a></li><li><a href="cluster-deployer.html">Deployer</a></li><li><a href="cluster-listener.html">ClusterListener</a></li></ul></div><div><h2>web.xml</h2><ul><li><a href="filter.html">Filter</a></li></ul></div><div><h2>Other</h2><ul><li><a href="runtime-attributes.html">Runtime attributes</a></li><li><a href="systemprops.html">System properties</a></li><li><a href="jaspic.html">JASPIC</a></li></ul></div></nav></div></div><div id="mainRight"><div id="content"><h2>The HTTP2 Upgrade Protocol</h2><h3 id="Table_of_Contents">Table of Contents</h3><div class="text"> |
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| 5 | <ul><li><a href="#Introduction">Introduction</a></li><li><a href="#Attributes">Attributes</a><ol><li><a href="#Common_Attributes">Common Attributes</a></li><li><a href="#Standard_Implementation">Standard Implementation</a></li></ol></li><li><a href="#Nested_Components">Nested Components</a></li><li><a href="#Special_Features">Special Features</a></li></ul> |
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| 6 | </div><h3 id="Introduction">Introduction</h3><div class="text"> |
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| 7 | |||
| 8 | <p>The <strong>HTTP Upgrade Protocol</strong> element represents an |
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| 9 | <strong>Upgrade Protocol</strong> component that supports the HTTP/2 protocol. |
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| 10 | An instance of this component must be associated with an existing |
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| 11 | <a href="http.html">HTTP/1.1 Connector</a>.</p> |
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| 12 | |||
| 13 | <p>HTTP/2 connectors use non-blocking I/O, only utilising a container thread |
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| 14 | from the thread pool when there is data to read and write. However, because |
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| 15 | the Servlet API is fundamentally blocking, each HTTP/2 stream requires a |
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| 16 | dedicated container thread for the duration of that stream.</p> |
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| 17 | |||
| 18 | <p>Requests processed using HTTP/2 will have the following additional request |
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| 19 | attributes available:</p> |
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| 20 | <ul> |
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| 21 | <li><code>org.apache.coyote.connectionID</code> will return the HTTP/2 |
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| 22 | connection ID</li> |
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| 23 | <li><code>org.apache.coyote.streamID</code> will return the HTTP/2 stream |
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| 24 | ID</li> |
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| 25 | </ul> |
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| 26 | |||
| 27 | </div><h3 id="Attributes">Attributes</h3><div class="text"> |
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| 28 | |||
| 29 | <div class="subsection"><h4 id="Common_Attributes">Common Attributes</h4><div class="text"> |
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| 30 | |||
| 31 | <p>All implementations of <strong>Upgrade Protocol</strong> support the |
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| 32 | following attributes:</p> |
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| 33 | |||
| 34 | <table class="defaultTable"><tr><th style="width: 15%;"> |
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| 35 | Attribute |
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| 36 | </th><th style="width: 85%;"> |
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| 37 | Description |
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| 38 | </th></tr><tr id="Attributes_Common Attributes_className"><td><strong><code class="attributeName">className</code></strong></td><td> |
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| 39 | <p>This must be <code>org.apache.coyote.http2.Http2Protocol</code>.</p> |
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| 40 | </td></tr></table> |
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| 41 | |||
| 42 | </div></div> |
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| 43 | |||
| 44 | <div class="subsection"><h4 id="Standard_Implementation">Standard Implementation</h4><div class="text"> |
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| 45 | |||
| 46 | <p>The HTTP/2 <strong>Upgrade Protocol</strong> implementation supports the |
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| 47 | following attributes in addition to the common attributes listed above.</p> |
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| 48 | |||
| 49 | <table class="defaultTable"><tr><th style="width: 15%;"> |
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| 50 | Attribute |
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| 51 | </th><th style="width: 85%;"> |
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| 52 | Description |
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| 53 | </th></tr><tr id="Attributes_Standard Implementation_allowedTrailerHeaders"><td><code class="attributeName">allowedTrailerHeaders</code></td><td> |
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| 54 | <p>By default Tomcat will ignore all trailer headers when processing |
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| 55 | HTTP/2 connections. For a header to be processed, it must be added to this |
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| 56 | comma-separated list of header names.</p> |
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| 57 | </td></tr><tr id="Attributes_Standard Implementation_compressibleMimeType"><td><code class="attributeName">compressibleMimeType</code></td><td> |
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| 58 | <p>The value is a comma separated list of MIME types for which HTTP |
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| 59 | compression may be used. |
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| 60 | The default value is |
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| 61 | <code> |
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| 62 | text/html,text/xml,text/plain,text/css,text/javascript,application/javascript,application/json,application/xml |
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| 63 | </code>. |
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| 64 | </p> |
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| 65 | </td></tr><tr id="Attributes_Standard Implementation_compression"><td><code class="attributeName">compression</code></td><td> |
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| 66 | <p>The HTTP/2 protocol may use compression in an attempt to save server |
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| 67 | bandwidth. The acceptable values for the parameter is "off" (disable |
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| 68 | compression), "on" (allow compression, which causes text data to be |
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| 69 | compressed), "force" (forces compression in all cases), or a numerical |
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| 70 | integer value (which is equivalent to "on", but specifies the minimum |
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| 71 | amount of data before the output is compressed). If the content-length is |
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| 72 | not known and compression is set to "on" or more aggressive, the output |
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| 73 | will also be compressed. If not specified, this attribute is set to |
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| 74 | "off".</p> |
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| 75 | <p><em>Note</em>: There is a tradeoff between using compression (saving |
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| 76 | your bandwidth) and using the sendfile feature (saving your CPU cycles). |
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| 77 | If the connector supports the sendfile feature, e.g. the NIO2 connector, |
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| 78 | using sendfile will take precedence over compression. The symptoms will |
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| 79 | be that static files greater that 48 Kb will be sent uncompressed. |
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| 80 | You can turn off sendfile by setting <code>useSendfile</code> attribute |
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| 81 | of the protocol, as documented below, or change the sendfile usage |
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| 82 | threshold in the configuration of the |
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| 83 | <a href="../default-servlet.html">DefaultServlet</a> in the default |
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| 84 | <code>conf/web.xml</code> or in the <code>web.xml</code> of your web |
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| 85 | application. |
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| 86 | </p> |
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| 87 | </td></tr><tr id="Attributes_Standard Implementation_compressionMinSize"><td><code class="attributeName">compressionMinSize</code></td><td> |
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| 88 | <p>If <strong>compression</strong> is set to "on" then this attribute |
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| 89 | may be used to specify the minimum amount of data before the output is |
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| 90 | compressed. If not specified, this attribute is defaults to "2048".</p> |
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| 91 | </td></tr><tr id="Attributes_Standard Implementation_discardRequestsAndResponses"><td><code class="attributeName">discardRequestsAndResponses</code></td><td> |
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| 92 | <p>A boolean value which can be used to enable or disable the recycling |
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| 93 | of the container internal request and response processing objects. If set |
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| 94 | to <code>true</code> the request and response objects will be set for |
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| 95 | garbage collection after every request, otherwise they will be reused. |
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| 96 | If not specified, this attribute is set to <code>false</code>.</p> |
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| 97 | </td></tr><tr id="Attributes_Standard Implementation_initialWindowSize"><td><code class="attributeName">initialWindowSize</code></td><td> |
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| 98 | <p>Controls the initial size of the flow control window for streams that |
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| 99 | Tomcat advertises to clients. If not specified, the default value of |
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| 100 | <code>65535</code> is used.</p> |
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| 101 | </td></tr><tr id="Attributes_Standard Implementation_keepAliveTimeout"><td><code class="attributeName">keepAliveTimeout</code></td><td> |
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| 102 | <p>The time, in milliseconds, that Tomcat will wait between HTTP/2 frames |
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| 103 | when there is no active Stream before closing the connection. Negative |
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| 104 | values will be treated as an infinite timeout. If not specified, a default |
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| 105 | value of <code>20000</code> will be used.</p> |
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| 106 | </td></tr><tr id="Attributes_Standard Implementation_maxConcurrentStreamExecution"><td><code class="attributeName">maxConcurrentStreamExecution</code></td><td> |
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| 107 | <p>The controls the maximum number of streams for any one connection that |
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| 108 | can be allocated threads from the container thread pool. If more streams |
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| 109 | are active than threads are available, those streams will have to wait |
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| 110 | for a stream to become available. If not specified, the default value of |
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| 111 | <code>20</code> will be used.</p> |
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| 112 | </td></tr><tr id="Attributes_Standard Implementation_maxConcurrentStreams"><td><code class="attributeName">maxConcurrentStreams</code></td><td> |
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| 113 | <p>The controls the maximum number of active streams permitted for any one |
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| 114 | connection. If a client attempts to open more active streams than this |
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| 115 | limit, the stream will be reset with a <code>STREAM_REFUSED</code> error. |
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| 116 | If not specified, the default value of <code>100</code> will be used.</p> |
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| 117 | </td></tr><tr id="Attributes_Standard Implementation_maxHeaderCount"><td><code class="attributeName">maxHeaderCount</code></td><td> |
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| 118 | <p>The maximum number of headers in a request that is allowed by the |
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| 119 | container. A request that contains more headers than the specified limit |
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| 120 | will be rejected. A value of less than 0 means no limit. |
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| 121 | If not specified, a default of 100 is used.</p> |
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| 122 | </td></tr><tr id="Attributes_Standard Implementation_maxHeaderSize"><td><code class="attributeName">maxHeaderSize</code></td><td> |
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| 123 | <p>The maximum total size for all headers in a request that is allowed by |
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| 124 | the container. Total size for a header is calculated as the uncompressed |
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| 125 | size of the header name in bytes, plus the uncompressed size of the header |
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| 126 | value in bytes plus an HTTP/2 overhead of 3 bytes per header. A request |
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| 127 | that contains a set of headers that requires more than the specified limit |
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| 128 | will be rejected. A value of less than 0 means no limit. If not specified, |
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| 129 | a default of 8192 is used.</p> |
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| 130 | </td></tr><tr id="Attributes_Standard Implementation_maxTrailerCount"><td><code class="attributeName">maxTrailerCount</code></td><td> |
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| 131 | <p>The maximum number of trailer headers in a request that is allowed by |
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| 132 | the container. A request that contains more trailer headers than the |
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| 133 | specified limit will be rejected. A value of less than 0 means no limit. |
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| 134 | If not specified, a default of 100 is used.</p> |
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| 135 | </td></tr><tr id="Attributes_Standard Implementation_maxTrailerSize"><td><code class="attributeName">maxTrailerSize</code></td><td> |
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| 136 | <p>The maximum total size for all trailer headers in a request that is |
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| 137 | allowed by the container. Total size for a header is calculated as the |
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| 138 | uncompressed size of the header name in bytes, plus the uncompressed size |
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| 139 | of the header value in bytes plus an HTTP/2 overhead of 3 bytes per |
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| 140 | header. A request that contains a set of trailer headers that requires |
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| 141 | more than the specified limit will be rejected. A value of less than 0 |
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| 142 | means no limit. If not specified, a default of 8192 is used.</p> |
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| 143 | </td></tr><tr id="Attributes_Standard Implementation_noCompressionStrongETag"><td><code class="attributeName">noCompressionStrongETag</code></td><td> |
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| 144 | <p>This flag configures whether resources with a stong ETag will be |
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| 145 | considered for compression. If <code>true</code>, resources with a strong |
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| 146 | ETag will not be compressed. The default value is <code>true</code>.</p> |
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| 147 | <p>This attribute is deprecated. It will be removed in Tomcat 10 onwards |
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| 148 | where it will be hard-coded to <code>true</code>.</p> |
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| 149 | </td></tr><tr id="Attributes_Standard Implementation_noCompressionUserAgents"><td><code class="attributeName">noCompressionUserAgents</code></td><td> |
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| 150 | <p>The value is a regular expression (using <code>java.util.regex</code>) |
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| 151 | matching the <code>user-agent</code> header of HTTP clients for which |
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| 152 | compression should not be used, |
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| 153 | because these clients, although they do advertise support for the |
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| 154 | feature, have a broken implementation. |
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| 155 | The default value is an empty String (regexp matching disabled).</p> |
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| 156 | </td></tr><tr id="Attributes_Standard Implementation_overheadContinuationThreshold"><td><code class="attributeName">overheadContinuationThreshold</code></td><td> |
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| 157 | <p>The threshold below which the payload size of a non-final |
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| 158 | <code>CONTINUATION</code> frame will trigger an increase in the overhead |
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| 159 | count (see <strong>overheadCountFactor</strong>). The overhead count will |
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| 160 | be increased by <code>overheadContinuationThreshold/payloadSize</code> so |
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| 161 | that the smaller the <code>CONTINUATION</code> frame, the greater the |
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| 162 | increase in the overhead count. A value of zero or less disables the |
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| 163 | checking of non-final <code>CONTINUATION</code> frames. If not specified, |
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| 164 | a default value of <code>1024</code> will be used.</p> |
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| 165 | </td></tr><tr id="Attributes_Standard Implementation_overheadCountFactor"><td><code class="attributeName">overheadCountFactor</code></td><td> |
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| 166 | <p>The factor to apply when counting overhead frames to determine if a |
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| 167 | connection has too high an overhead and should be closed. The overhead |
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| 168 | count starts at <code>-10 * overheadCountFactor</code>. The count is |
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| 169 | decreased by 20 for each data frame sent or received and each headers frame |
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| 170 | received. The count is increased by the <code>overheadCountFactor</code> |
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| 171 | for each setting, priority, priority update and ping frame received. If |
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| 172 | the overhead count exceeds zero, the connection is closed. A value of less |
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| 173 | than <code>1</code> disables this protection. In normal usage a value of |
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| 174 | approximately <code>20</code> or higher will close the connection before |
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| 175 | any streams can complete. If not specified, a default value of |
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| 176 | <code>10</code> will be used.</p> |
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| 177 | </td></tr><tr id="Attributes_Standard Implementation_overheadResetFactor"><td><code class="attributeName">overheadResetFactor</code></td><td> |
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| 178 | <p>The amount by which the overhead count (see |
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| 179 | <strong>overheadCountFactor</strong>) will be increased for each reset |
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| 180 | frame received or sent. If not specified, a default value of |
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| 181 | <code>50</code> will be used. A value of less than zero will be treated as |
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| 182 | zero.</p> |
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| 183 | </td></tr><tr id="Attributes_Standard Implementation_overheadDataThreshold"><td><code class="attributeName">overheadDataThreshold</code></td><td> |
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| 184 | <p>The threshold below which the average payload size of the current and |
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| 185 | previous non-final <code>DATA</code> frames will trigger an increase in |
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| 186 | the overhead count (see <strong>overheadCountFactor</strong>). The |
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| 187 | overhead count will be increased by |
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| 188 | <code>overheadDataThreshold/average</code> so that the smaller the |
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| 189 | average, the greater the increase in the overhead count. A value of zero |
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| 190 | or less disables the checking of non-final <code>DATA</code> frames. If |
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| 191 | not specified, a default value of <code>1024</code> will be used.</p> |
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| 192 | </td></tr><tr id="Attributes_Standard Implementation_overheadWindowUpdateThreshold"><td><code class="attributeName">overheadWindowUpdateThreshold</code></td><td> |
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| 193 | <p>The threshold below which the average size of current and previous |
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| 194 | <code>WINDOW_UPDATE</code> frame will trigger an increase in the overhead |
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| 195 | count (see <strong>overheadCountFactor</strong>). The overhead count will |
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| 196 | be increased by <code>overheadWindowUpdateThreshold/average</code> so |
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| 197 | that the smaller the average, the greater the increase in the overhead |
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| 198 | count. A value of zero or less disables the checking of |
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| 199 | <code>WINDOW_UPDATE</code> frames. If not specified, a default value of |
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| 200 | <code>1024</code> will be used.</p> |
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| 201 | </td></tr><tr id="Attributes_Standard Implementation_readTimeout"><td><code class="attributeName">readTimeout</code></td><td> |
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| 202 | <p>The time, in milliseconds, that Tomcat will wait for additional data |
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| 203 | when a partial HTTP/2 frame has been received. Negative values will be |
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| 204 | treated as an infinite timeout. If not specified, a default value of |
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| 205 | <code>5000</code> will be used.</p> |
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| 206 | </td></tr><tr id="Attributes_Standard Implementation_streamReadTimeout"><td><code class="attributeName">streamReadTimeout</code></td><td> |
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| 207 | <p>The time, in milliseconds, that Tomcat will wait for additional data |
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| 208 | frames to arrive for the stream when an application is performing a |
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| 209 | blocking I/O read and additional data is required. Negative values will be |
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| 210 | treated as an infinite timeout. If not specified, a default value of |
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| 211 | <code>20000</code> will be used.</p> |
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| 212 | </td></tr><tr id="Attributes_Standard Implementation_streamWriteTimeout"><td><code class="attributeName">streamWriteTimeout</code></td><td> |
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| 213 | <p>The time, in milliseconds, that Tomcat will wait for additional window |
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| 214 | update frames to arrive for the stream and/or connection when an |
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| 215 | application is performing a blocking I/O write and the stream and/or |
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| 216 | connection flow control window is too small for the write to complete. |
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| 217 | Negative values will be treated as an infinite timeout. If not specified, |
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| 218 | a default value of <code>20000</code> will be used.</p> |
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| 219 | </td></tr><tr id="Attributes_Standard Implementation_useSendfile"><td><code class="attributeName">useSendfile</code></td><td> |
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| 220 | <p>Use this boolean attribute to enable or disable sendfile capability. |
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| 221 | The default value is <code>true</code>.</p> |
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| 222 | <p>This setting is ignored, and the sendfile capability disabled, if the |
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| 223 | <strong>useAsyncIO</strong> attribute of the associated |
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| 224 | <strong>Connector</strong> is set to <code>false</code>.</p> |
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| 225 | <p>The HTTP/2 sendfile capability uses <a href="https://docs.oracle.com/javase/8/docs/api/java/nio/MappedByteBuffer.html">MappedByteBuffer</a> which is known to cause file locking on Windows.</p> |
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| 226 | </td></tr><tr id="Attributes_Standard Implementation_writeTimeout"><td><code class="attributeName">writeTimeout</code></td><td> |
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| 227 | <p>The time, in milliseconds, that Tomcat will wait to write additional |
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| 228 | data when an HTTP/2 frame has been partially written. Negative values will |
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| 229 | be treated as an infinite timeout. If not specified, a default value of |
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| 230 | <code>5000</code> will be used.</p> |
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| 231 | </td></tr></table> |
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| 232 | |||
| 233 | <p>The HTTP/2 upgrade protocol will also inherit the following attributes from |
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| 234 | the <a href="http.html">HTTP Connector</a> within which it is nested:</p> |
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| 235 | |||
| 236 | <ul> |
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| 237 | <li>maxCookieCount</li> |
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| 238 | <li>maxParameterCount</li> |
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| 239 | <li>maxPartCount</li> |
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| 240 | <li>maxPartHeaderSize</li> |
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| 241 | <li>maxPostSize</li> |
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| 242 | <li>maxSavePostSize</li> |
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| 243 | <li>server</li> |
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| 244 | <li>serverRemoveAppProvidedValues</li> |
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| 245 | </ul> |
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| 246 | |||
| 247 | </div></div> |
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| 248 | |||
| 249 | </div><h3 id="Nested_Components">Nested Components</h3><div class="text"> |
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| 250 | |||
| 251 | <p>This component does not support any nested components.</p> |
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| 252 | |||
| 253 | </div><h3 id="Special_Features">Special Features</h3><div class="text"> |
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| 254 | |||
| 255 | <p>This component does not support any special features.</p> |
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| 256 | |||
| 257 | </div></div></div></div></div><footer><div id="footer"> |
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| 258 | Copyright © 1999-2025, The Apache Software Foundation |
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| 259 | <br> |
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| 260 | Apache Tomcat, Tomcat, Apache, the Apache Tomcat logo and the Apache logo |
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| 261 | are either registered trademarks or trademarks of the Apache Software |
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| 262 | Foundation. |
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| 263 | </div></footer></div></body></html> |