178 lines
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178 lines
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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 8 (8.0.53) - WebSocket How-To</title><script type="application/javascript" data-comments-identifier="tomcat-8.0-doc/web-socket-howto">
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</script></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 8</h1><div class="versionInfo">
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Version 8.0.53,
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<time datetime="2018-06-29">Jun 29 2018</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://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="host-manager-howto.html">6) Host Manager</a></li><li><a href="realm-howto.html">7) Realms and AAA</a></li><li><a href="security-manager-howto.html">8) Security Manager</a></li><li><a href="jndi-resources-howto.html">9) JNDI Resources</a></li><li><a href="jndi-datasource-examples-howto.html">10) JDBC DataSources</a></li><li><a href="class-loader-howto.html">11) Classloading</a></li><li><a href="jasper-howto.html">12) JSPs</a></li><li><a href="ssl-howto.html">13) SSL/TLS</a></li><li><a href="ssi-howto.html">14) SSI</a></li><li><a href="cgi-howto.html">15) CGI</a></li><li><a href="proxy-howto.html">16) Proxy Support</a></li><li><a href="mbeans-descriptors-howto.html">17) MBeans Descriptors</a></li><li><a href="default-servlet.html">18) Default Servlet</a></li><li><a href="cluster-howto.html">19) Clustering</a></li><li><a href="balancer-howto.html">20) Load Balancer</a></li><li><a href="connectors.html">21) Connectors</a></li><li><a href="monitoring.html">22) Monitoring and Management</a></li><li><a href="logging.html">23) Logging</a></li><li><a href="apr.html">24) APR/Native</a></li><li><a href="virtual-hosting-howto.html">25) Virtual Hosting</a></li><li><a href="aio.html">26) Advanced IO</a></li><li><a href="extras.html">27) Additional Components</a></li><li><a href="maven-jars.html">28) Mavenized</a></li><li><a href="security-howto.html">29) Security Considerations</a></li><li><a href="windows-service-howto.html">30) Windows Service</a></li><li><a href="windows-auth-howto.html">31) Windows Authentication</a></li><li><a href="jdbc-pool.html">32) Tomcat's JDBC Pool</a></li><li><a href="web-socket-howto.html">33) WebSocket</a></li><li><a href="rewrite.html">34) 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="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://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">
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<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>
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</div><h3 id="Overview">Overview</h3><div class="text">
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<p>Tomcat provides support for WebSocket as defined by
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<a href="https://tools.ietf.org/html/rfc6455">RFC 6455</a>.</p>
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</div><h3 id="Application_development">Application development</h3><div class="text">
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<p>Tomcat implements the Java WebSocket 1.1 API defined by <a href="https://www.jcp.org/en/jsr/detail?id=356">JSR-356</a>.</p>
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<p>There are several example applications that demonstrate how the WebSocket API
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can be used. You will need to look at both the client side <a href="https://svn.apache.org/viewvc/tomcat/trunk/webapps/examples/websocket/">
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HTML</a> and the server side <a href="https://svn.apache.org/viewvc/tomcat/trunk/webapps/examples/WEB-INF/classes/websocket/">
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code</a>.</p>
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</div><h3 id="Production_usage">Production usage</h3><div class="text">
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<p>Although the WebSocket implementation does work with any of the HTTP
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connectors, it is not recommended to the WebSocket with the BIO HTTP connector
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as the typical uses of WebSocket (large numbers of mostly idle connections) is
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not a good fit for the HTTP BIO connector which requires that one thread is
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allocated per connection regardless of whether or not the connection is idle.
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</p>
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<p>It has been reported (<a href="https://bz.apache.org/bugzilla/show_bug.cgi?id=56304">56304</a>) that Linux can take large numbers of
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minutes to report dropped connections. When using WebSocket with the BIO HTTP
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connector this can result in threads blocking on writes for this period. This is
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likely to be undesirable. The time taken for the connection to be reported as
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dropped can be reduced by using the kernel network parameter
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<code>/proc/sys/net/ipv4/tcp_retries2</code>. Alternatively, one of the other
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HTTP connectors may be used as they utilise non-blocking IO enabling Tomcat to
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implement its own timeout mechanism to handle these cases.</p>
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</div><h3 id="Tomcat_WebSocket_specific_configuration">Tomcat WebSocket specific configuration</h3><div class="text">
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<p>Tomcat provides a number of Tomcat specific configuration options for
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WebSocket. It is anticipated that these will be absorbed into the WebSocket
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specification over time.</p>
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<p>The write timeout used when sending WebSocket messages in blocking mode
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defaults to 20000 milliseconds (20 seconds). This may be changed by setting
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the property <code>org.apache.tomcat.websocket.BLOCKING_SEND_TIMEOUT</code>
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in the user properties collection attached to the WebSocket session. The
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value assigned to this property should be a <code>Long</code> and represents
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the timeout to use in milliseconds. For an infinite timeout, use
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<code>-1</code>.</p>
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<p>If the application does not define a <code>MessageHandler.Partial</code> for
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incoming binary messages, any incoming binary messages must be buffered so
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the entire message can be delivered in a single call to the registered
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<code>MessageHandler.Whole</code> for binary messages. The default buffer
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size for binary messages is 8192 bytes. This may be changed for a web
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application by setting the servlet context initialization parameter
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<code>org.apache.tomcat.websocket.binaryBufferSize</code> to the desired
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value in bytes.</p>
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<p>If the application does not define a <code>MessageHandler.Partial</code> for
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incoming text messages, any incoming text messages must be buffered so the
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entire message can be delivered in a single call to the registered
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<code>MessageHandler.Whole</code> for text messages. The default buffer size
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for text messages is 8192 bytes. This may be changed for a web application by
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setting the servlet context initialization parameter
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<code>org.apache.tomcat.websocket.textBufferSize</code> to the desired value
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in bytes.</p>
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<p>The Java WebSocket specification 1.0 does not permit programmatic deployment
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after the first endpoint has started a WebSocket handshake. By default,
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Tomcat continues to permit additional programmatic deployment. This
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behavior is controlled by the
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<code>org.apache.tomcat.websocket.noAddAfterHandshake</code> servlet context
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initialization parameter. The default may be changed by setting the
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<code>org.apache.tomcat.websocket.STRICT_SPEC_COMPLIANCE</code> system
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property to <code>true</code> but any explicit setting on the servlet context
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will always take priority.</p>
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<p>The Java WebSocket 1.0 specification requires that callbacks for
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asynchronous writes are performed on a different thread to the thread that
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initiated the write. Since the container thread pool is not exposed via the
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Servlet API, the WebSocket implementation has to provide its own thread pool.
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This thread pool is controlled by the following servlet context
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initialization parameters:</p>
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<ul>
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<li><code>org.apache.tomcat.websocket.executorCoreSize</code>: The core
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size of the executor thread pool. If not set, the default of 0 (zero)
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is used. Note that the maximum permitted size of the executor thread
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pool is hard coded to <code>Integer.MAX_VALUE</code> which effectively
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means it is unlimited.</li>
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<li><code>org.apache.tomcat.websocket.executorKeepAliveTimeSeconds</code>:
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The maximum time an idle thread will remain in the executor thread pool
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until it is terminated. If not specified, the default of 60 seconds is
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used.</li>
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</ul>
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<p>When using the WebSocket client to connect to server endpoints, the timeout
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for IO operations while establishing the connection is controlled by the
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<code>userProperties</code> of the provided
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<code>javax.websocket.ClientEndpointConfig</code>. The property is
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<code>org.apache.tomcat.websocket.IO_TIMEOUT_MS</code> and is the
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timeout as a <code>String</code> in milliseconds. The default is 5000 (5
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seconds).</p>
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<p>When using the WebSocket client to connect to secure server endpoints, the
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client SSL configuration is controlled by the <code>userProperties</code>
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of the provided <code>javax.websocket.ClientEndpointConfig</code>. The
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following user properties are supported:</p>
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<ul>
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<li><code>org.apache.tomcat.websocket.SSL_CONTEXT</code></li>
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<li><code>org.apache.tomcat.websocket.SSL_PROTOCOLS</code></li>
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<li><code>org.apache.tomcat.websocket.SSL_TRUSTSTORE</code></li>
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<li><code>org.apache.tomcat.websocket.SSL_TRUSTSTORE_PWD</code></li>
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</ul>
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<p>The default truststore password is <code>changeit</code>.</p>
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<p>If the <code>org.apache.tomcat.websocket.SSL_CONTEXT</code> property is
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set then the <code>org.apache.tomcat.websocket.SSL_TRUSTSTORE</code> and
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<code>org.apache.tomcat.websocket.SSL_TRUSTSTORE_PWD</code> properties
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will be ignored.</p>
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<p>For secure server end points, host name verification is enabled by default.
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To bypass this verification (not recommended), it is necessary to provide a
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custom <code>SSLContext</code> via the
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<code>org.apache.tomcat.websocket.SSL_CONTEXT</code> user property. The
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custom <code>SSLContext</code> must be configured with a custom
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<code>TrustManager</code> that extends
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<code>javax.net.ssl.X509ExtendedTrustManager</code>. The desired verification
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(or lack of verification) can then be controlled by appropriate
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implementations of the individual abstract methods.</p>
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<p>When using the WebSocket client to connect to server endpoints, the number of
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HTTP redirects that the client will follow is controlled by the
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<code>userProperties</code> of the provided
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<code>javax.websocket.ClientEndpointConfig</code>. The property is
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<ocde>org.apache.tomcat.websocket.MAX_REDIRECTIONS</ocde>. The default value
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is 20. Redirection support can be disabled by configuring a value of zero.</p>
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</div><div class="noprint"><h3 id="comments_section">
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Comments
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</h3><div class="text"><p class="notice"><strong>Notice: </strong>This comments section collects your suggestions
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on improving documentation for Apache Tomcat.<br><br>
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If you have trouble and need help, read
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<a href="https://tomcat.apache.org/findhelp.html">Find Help</a> page
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and ask your question on the tomcat-users
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<a href="https://tomcat.apache.org/lists.html">mailing list</a>.
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Do not ask such questions here. This is not a Q&A section.<br><br>
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The Apache Comments System is explained <a href="./comments.html">here</a>.
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Comments may be removed by our moderators if they are either
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implemented or considered invalid/off-topic.
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</p><div id="comments_thread"></div></div></div></div></div></div></div><footer><div id="footer">
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