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<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 11 (11.0.20) - WebSocket How-To</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 11</h1><div class="versionInfo">
Version 11.0.20,
<time datetime="2026-03-16">Mar 16 2026</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="https://cwiki.apache.org/confluence/display/TOMCAT/FAQ">FAQ</a></li></ul></div><div><h2>User Guide</h2><ul><li><a href="introduction.html">1) Introduction</a></li><li><a href="setup.html">2) Setup</a></li><li><a href="appdev/index.html">3) First webapp</a></li><li><a href="deployer-howto.html">4) Deployer</a></li><li><a href="manager-howto.html">5) Manager</a></li><li><a href="host-manager-howto.html">6) Host Manager</a></li><li><a href="realm-howto.html">7) Realms and AAA</a></li><li><a href="jndi-resources-howto.html">8) JNDI Resources</a></li><li><a href="jndi-datasource-examples-howto.html">9) JDBC DataSources</a></li><li><a href="class-loader-howto.html">10) Classloading</a></li><li><a href="jasper-howto.html">11) JSPs</a></li><li><a href="ssl-howto.html">12) SSL/TLS</a></li><li><a href="ssi-howto.html">13) SSI</a></li><li><a href="cgi-howto.html">14) CGI</a></li><li><a href="proxy-howto.html">15) Proxy Support</a></li><li><a href="mbeans-descriptors-howto.html">16) MBeans Descriptors</a></li><li><a href="default-servlet.html">17) Default Servlet</a></li><li><a href="cluster-howto.html">18) Clustering</a></li><li><a href="balancer-howto.html">19) Load Balancer</a></li><li><a href="connectors.html">20) Connectors</a></li><li><a href="monitoring.html">21) Monitoring and Management</a></li><li><a href="logging.html">22) Logging</a></li><li><a href="apr.html">23) APR/Native</a></li><li><a href="virtual-hosting-howto.html">24) Virtual Hosting</a></li><li><a href="aio.html">25) Advanced IO</a></li><li><a href="maven-jars.html">26) Mavenized</a></li><li><a href="security-howto.html">27) Security Considerations</a></li><li><a href="windows-service-howto.html">28) Windows Service</a></li><li><a href="windows-auth-howto.html">29) Windows Authentication</a></li><li><a href="jdbc-pool.html">30) Tomcat's JDBC Pool</a></li><li><a href="web-socket-howto.html">31) WebSocket</a></li><li><a href="rewrite.html">32) Rewrite</a></li><li><a href="cdi.html">33) CDI 2 and JAX-RS</a></li><li><a href="graal.html">34) AOT/GraalVM Support</a></li></ul></div><div><h2>Reference</h2><ul><li><a href="RELEASE-NOTES.txt">Release Notes</a></li><li><a href="config/index.html">Configuration</a></li><li><a href="api/index.html">Tomcat Javadocs</a></li><li><a href="servletapi/index.html">Servlet 6.1 Javadocs</a></li><li><a href="jspapi/index.html">JSP 4.0 Javadocs</a></li><li><a href="elapi/index.html">EL 6.0 Javadocs</a></li><li><a href="websocketapi/index.html">WebSocket 2.2 Javadocs</a></li><li><a href="jaspicapi/index.html">Authentication 3.1 Javadocs</a></li><li><a href="annotationapi/index.html">Annotations 3.0 Javadocs</a></li><li><a href="https://tomcat.apache.org/connectors-doc/">JK 1.2 Documentation</a></li></ul></div><div><h2>Apache Tomcat Development</h2><ul><li><a href="building.html">Building</a></li><li><a href="changelog.html">Changelog</a></li><li><a href="https://cwiki.apache.org/confluence/display/TOMCAT/Tomcat+Versions">Status</a></li><li><a href="developers.html">Developers</a></li><li><a href="architecture/index.html">Architecture</a></li><li><a href="tribes/introduction.html">Tribes</a></li></ul></div></nav></div></div><div id="mainRight"><div id="content"><h2>WebSocket How-To</h2><h3 id="Table_of_Contents">Table of Contents</h3><div class="text">
<ul><li><a href="#Overview">Overview</a></li><li><a href="#Application_development">Application development</a></li><li><a href="#Tomcat_WebSocket_specific_configuration">Tomcat WebSocket specific configuration</a></li></ul>
</div><h3 id="Overview">Overview</h3><div class="text">
<p>Tomcat provides support for WebSocket as defined by
<a href="https://tools.ietf.org/html/rfc6455">RFC 6455</a>.</p>
</div><h3 id="Application_development">Application development</h3><div class="text">
<p>Tomcat implements the Jakarta WebSocket 2.1 API defined by the <a href="https://projects.eclipse.org/projects/ee4j.websocket">Jakarta
WebSocket</a> project.</p>
<p>There are several example applications that demonstrate how the WebSocket API
can be used. You will need to look at both the client side <a href="https://github.com/apache/tomcat/tree/main/webapps/examples/websocket">
HTML</a> and the server side <a href="https://github.com/apache/tomcat/tree/main/webapps/examples/WEB-INF/classes/websocket">
code</a>.</p>
</div><h3 id="Tomcat_WebSocket_specific_configuration">Tomcat WebSocket specific configuration</h3><div class="text">
<p>Tomcat provides a number of Tomcat specific configuration options for
WebSocket. It is anticipated that these will be absorbed into the WebSocket
specification over time.</p>
<p>The write timeout used when sending WebSocket messages in blocking mode
defaults to 20000 milliseconds (20 seconds). This may be changed by setting
the property <code>org.apache.tomcat.websocket.BLOCKING_SEND_TIMEOUT</code>
in the user properties collection attached to the WebSocket session. The
value assigned to this property should be a <code>Long</code> and represents
the timeout to use in milliseconds. For an infinite timeout, use
<code>-1</code>.</p>
<p>The time Tomcat waits for a peer to send a WebSocket session close message
after Tomcat has sent a close message to the peer defaults to 30000
milliseconds (30 seconds). This may be changed by setting the property
<code>org.apache.tomcat.websocket.SESSION_CLOSE_TIMEOUT</code> in the user
properties collection attached to the WebSocket session. The value assigned
to this property should be a <code>Long</code> and represents the timeout to
use in milliseconds. Values less than or equal to zero will be ignored.</p>
<p>The write timeout Tomcat uses when writing a session close message when the
close is abnormal defaults to 50 milliseconds. This may be changed by setting
the property
<code>org.apache.tomcat.websocket.ABNORMAL_SESSION_CLOSE_SEND_TIMEOUT</code>
in the user properties collection attached to the WebSocket session. The
value assigned to this property should be a <code>Long</code> and represents
the timeout to use in milliseconds. Values less than or equal to zero will be
ignored.</p>
<p>In addition to the <code>Session.setMaxIdleTimeout(long)</code> method which
is part of the Jakarta WebSocket API, Tomcat provides greater control of the
timing out the session due to lack of activity. Setting the property
<code>org.apache.tomcat.websocket.READ_IDLE_TIMEOUT_MS</code> in the user
properties collection attached to the WebSocket session will trigger a
session timeout if no WebSocket message is received for the specified number
of milliseconds. Setting the property
<code>org.apache.tomcat.websocket.WRITE_IDLE_TIMEOUT_MS</code> will trigger a
session timeout if no WebSocket message is sent for the specified number of
milliseconds. These can be used separately or together, with or without
<code>Session.setMaxIdleTimeout(long)</code>. If the associated property is
not specified, the read and/or write idle timeout will be applied.</p>
<p>If the application does not define a <code>MessageHandler.Partial</code> for
incoming binary messages, any incoming binary messages must be buffered so
the entire message can be delivered in a single call to the registered
<code>MessageHandler.Whole</code> for binary messages. The default buffer
size for binary messages is 8192 bytes. This may be changed for a web
application by setting the servlet context initialization parameter
<code>org.apache.tomcat.websocket.binaryBufferSize</code> to the desired
value in bytes.</p>
<p>If the application does not define a <code>MessageHandler.Partial</code> for
incoming text messages, any incoming text messages must be buffered so the
entire message can be delivered in a single call to the registered
<code>MessageHandler.Whole</code> for text messages. The default buffer size
for text messages is 8192 bytes. This may be changed for a web application by
setting the servlet context initialization parameter
<code>org.apache.tomcat.websocket.textBufferSize</code> to the desired value
in bytes.</p>
<p>When using the WebSocket client to connect to server endpoints, the timeout
for IO operations while establishing the connection is controlled by the
<code>userProperties</code> of the provided
<code>jakarta.websocket.ClientEndpointConfig</code>. The property is
<code>org.apache.tomcat.websocket.IO_TIMEOUT_MS</code> and is the
timeout as a <code>String</code> in milliseconds. The default is 5000 (5
seconds).</p>
<p>When using the WebSocket client to connect to server endpoints, the number of
HTTP redirects that the client will follow is controlled by the
<code>userProperties</code> of the provided
<code>jakarta.websocket.ClientEndpointConfig</code>. The property is
<ocde>org.apache.tomcat.websocket.MAX_REDIRECTIONS</ocde>. The default value
is 20. Redirection support can be disabled by configuring a value of zero.
</p>
<p>When using the WebSocket client to connect to a server endpoint that requires
BASIC or DIGEST authentication, the following user properties must be set:
</p>
<ul>
<li><code>org.apache.tomcat.websocket.WS_AUTHENTICATION_USER_NAME</code>
</li>
<li><code>org.apache.tomcat.websocket.WS_AUTHENTICATION_PASSWORD</code>
</li>
</ul>
<p>Optionally, the WebSocket client can be configured only to send
credentials if the server authentication challenge includes a specific realm
by defining that realm in the optional user property:</p>
<ul>
<li><code>org.apache.tomcat.websocket.WS_AUTHENTICATION_REALM</code></li>
</ul>
<p>When using the WebSocket client to connect to a server endpoint via a forward
proxy (also known as a gateway) that requires BASIC or DIGEST authentication,
the following user properties must be set:
</p>
<ul>
<li><code>org.apache.tomcat.websocket.WS_PROXY_AUTHENTICATION_USER_NAME
</code></li>
<li><code>org.apache.tomcat.websocket.WS_PROXY_AUTHENTICATION_PASSWORD
</code></li>
</ul>
<p>Optionally, the WebSocket client can be configured only to send
credentials if the server authentication challenge includes a specific realm
by defining that realm in the optional user property:</p>
<ul>
<li><code>org.apache.tomcat.websocket.WS_PROXY_AUTHENTICATION_REALM</code>
</li>
</ul>
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