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</script></head><body><div id="wrapper"><header><div id="header"><div><div><div class="logo noPrint"><a href="http://tomcat.apache.org/"><img alt="Tomcat Home" src="./images/tomcat.png"></a></div><div style="height: 1px;"></div><div class="asfLogo noPrint"><a href="http://www.apache.org/" target="_blank"><img src="./images/asf-feather.png" alt="The Apache Software Foundation" style="width: 266px; height: 83px;"></a></div><h1>Apache Tomcat 8</h1><div class="versionInfo">
Version 8.0.39,
<time datetime="2016-11-09">Nov 9 2016</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="http://wiki.apache.org/tomcat/FAQ">FAQ</a></li><li><a href="#comments_section">User Comments</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="realm-howto.html">6) Realms and AAA</a></li><li><a href="security-manager-howto.html">7) Security Manager</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="extras.html">26) Additional Components</a></li><li><a href="maven-jars.html">27) Mavenized</a></li><li><a href="security-howto.html">28) Security Considerations</a></li><li><a href="windows-service-howto.html">29) Windows Service</a></li><li><a href="windows-auth-howto.html">30) Windows Authentication</a></li><li><a href="jdbc-pool.html">31) Tomcat's JDBC Pool</a></li><li><a href="web-socket-howto.html">32) WebSocket</a></li><li><a href="rewrite.html">33) Rewrite</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 Javadocs</a></li><li><a href="jspapi/index.html">JSP 2.3 Javadocs</a></li><li><a href="elapi/index.html">EL 3.0 Javadocs</a></li><li><a href="websocketapi/index.html">WebSocket 1.1 Javadocs</a></li><li><a href="http://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="http://wiki.apache.org/tomcat/TomcatVersions">Status</a></li><li><a href="developers.html">Developers</a></li><li><a href="architecture/index.html">Architecture</a></li><li><a href="funcspecs/index.html">Functional Specs.</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="#Production_usage">Production usage</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="http://tools.ietf.org/html/rfc6455">RFC 6455</a>.</p>
</div><h3 id="Application_development">Application development</h3><div class="text">
<p>Tomcat implements the Java WebSocket 1.1 API defined by <a href="http://www.jcp.org/en/jsr/detail?id=356">JSR-356</a>.</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="http://svn.apache.org/viewvc/tomcat/trunk/webapps/examples/websocket/">
HTML</a> and the server side <a href="http://svn.apache.org/viewvc/tomcat/trunk/webapps/examples/WEB-INF/classes/websocket/">
code</a>.</p>
</div><h3 id="Production_usage">Production usage</h3><div class="text">
<p>Although the WebSocket implementation does work with any of the HTTP
connectors, it is not recommended to the WebSocket with the BIO HTTP connector
as the typical uses of WebSocket (large numbers of mostly idle connections) is
not a good fit for the HTTP BIO connector which requires that one thread is
allocated per connection regardless of whether or not the connection is idle.
</p>
<p>It has been reported (<a href="http://bz.apache.org/bugzilla/show_bug.cgi?id=56304">56304</a>) that Linux can take large numbers of
minutes to report dropped connections. When using WebSocket with the BIO HTTP
connector this can result in threads blocking on writes for this period. This is
likely to be undesirable. The time taken for the connection to be reported as
dropped can be reduced by using the kernel network parameter
<code>/proc/sys/net/ipv4/tcp_retries2</code>. Alternatively, one of the other
HTTP connectors may be used as they utilise non-blocking IO enabling Tomcat to
implement its own timeout mechanism to handle these cases.</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>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>The Java WebSocket specification 1.0 does not permit programmatic deployment
after the first endpoint has started a WebSocket handshake. By default,
Tomcat continues to permit additional programmatic deployment. This
behavior is controlled by the
<code>org.apache.tomcat.websocket.noAddAfterHandshake</code> servlet context
initialization parameter. The default may be changed by setting the
<code>org.apache.tomcat.websocket.STRICT_SPEC_COMPLIANCE</code> system
property to <code>true</code> but any explicit setting on the servlet context
will always take priority.</p>
<p>The Java WebSocket 1.0 specification requires that callbacks for
asynchronous writes are performed on a different thread to the thread that
initiated the write. Since the container thread pool is not exposed via the
Servlet API, the WebSocket implementation has to provide its own thread pool.
This thread pool is controlled by the following servlet context
initialization parameters:</p>
<ul>
<li><code>org.apache.tomcat.websocket.executorCoreSize</code>: The core
size of the executor thread pool. If not set, the default of 0 (zero)
is used. Note that the maximum permitted size of the executor thread
pool is hard coded to <code>Integer.MAX_VALUE</code> which effectively
means it is unlimited.</li>
<li><code>org.apache.tomcat.websocket.executorKeepAliveTimeSeconds</code>:
The maximum time an idle thread will remain in the executor thread pool
until it is terminated. If not specified, the default of 60 seconds is
used.</li>
</ul>
<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>javax.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 secure server endpoints, the
client SSL configuration is controlled by the <code>userProperties</code>
of the provided <code>javax.websocket.ClientEndpointConfig</code>. The
following user properties are supported:</p>
<ul>
<li><code>org.apache.tomcat.websocket.SSL_CONTEXT</code></li>
<li><code>org.apache.tomcat.websocket.SSL_PROTOCOLS</code></li>
<li><code>org.apache.tomcat.websocket.SSL_TRUSTSTORE</code></li>
<li><code>org.apache.tomcat.websocket.SSL_TRUSTSTORE_PWD</code></li>
</ul>
<p>The default truststore password is <code>changeit</code>.</p>
<p>If the <code>org.apache.tomcat.websocket.SSL_CONTEXT</code> property is
set then the <code>org.apache.tomcat.websocket.SSL_TRUSTSTORE</code> and
<code>org.apache.tomcat.websocket.SSL_TRUSTSTORE_PWD</code> properties
will be ignored.</p>
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