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Hongqing Liu

2014-05-10 16:32:51 +0800

<html><head><META http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>Apache Tomcat 6.0 (6.0.39) - Advanced IO and Tomcat</title><meta name="author" content="Remy Maucherat"><style type="text/css" media="print">

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</style></head><body bgcolor="#ffffff" text="#000000" link="#525D76" alink="#525D76" vlink="#525D76"><table border="0" width="100%" cellspacing="0"><tr><td><a href="http://tomcat.apache.org/"><img src="./images/tomcat.gif" align="right" alt="

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The Apache Tomcat Servlet/JSP Container

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" border="0"></a></td><td><h1><font face="arial,helvetica,sanserif">Apache Tomcat 6.0</font></h1><font face="arial,helvetica,sanserif">Version 6.0.39, Jan 27 2014</font></td><td><a href="http://www.apache.org/"><img src="./images/asf-logo.gif" align="right" alt="Apache Logo" border="0"></a></td></tr></table><table border="0" width="100%" cellspacing="4"><tr><td colspan="2"><hr noshade="noshade" size="1"></td></tr><tr><td width="20%" valign="top" nowrap="nowrap" class="noPrint"><p><strong>Links</strong></p><ul><li><a href="index.html">Docs Home</a></li><li><a href="http://wiki.apache.org/tomcat/FAQ">FAQ</a></li></ul><p><strong>User Guide</strong></p><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</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-descriptor-howto.html">16) MBean Descriptor</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></ul><p><strong>Reference</strong></p><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">Javadocs</a></li><li><a href="http://tomcat.apache.org/connectors-doc/">JK 1.2 Documentation</a></li></ul><p><strong>Apache Tomcat Development</strong></p><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></ul></td><td width="80%" valign="top" align="left" id="mainBody"><h1>Apache Tomcat 6.0</h1><h2>Advanced IO and Tomcat</h2><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Table of Contents"></a><a name="Table_of_Contents"><strong>Table of Contents</strong></a></font></td></tr><tr><td><blockquote>

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<ul><li><a href="#Introduction">Introduction</a></li><li><a href="#Comet_support">Comet support</a><ol><li><a href="#CometEvent">CometEvent</a></li><li><a href="#CometFilter">CometFilter</a></li><li><a href="#Example_code">Example code</a></li><li><a href="#Comet_timeouts">Comet timeouts</a></li></ol></li><li><a href="#Asynchronous_writes">Asynchronous writes</a></li></ul>

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</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Introduction"><strong>Introduction</strong></a></font></td></tr><tr><td><blockquote>

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<p>

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With usage of APR or NIO APIs as the basis of its connectors, Tomcat is

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able to provide a number of extensions over the regular blocking IO

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as provided with support for the Servlet API.

</p>

<p>

<b>IMPORTANT NOTE: Usage of these features requires using the APR or NIO

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HTTP connectors. The classic java.io HTTP connector and the AJP connectors

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do not support them.</b>

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</p>

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</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Comet support"></a><a name="Comet_support"><strong>Comet support</strong></a></font></td></tr><tr><td><blockquote>

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<p>

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Comet support allows a servlet to process IO asynchronously, receiving

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events when data is available for reading on the connection (rather than

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always using a blocking read), and writing data back on connections

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asynchronously (most likely responding to some event raised from some

other source).

</p>

<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="CometEvent"><strong>CometEvent</strong></a></font></td></tr><tr><td><blockquote>

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<p>

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Servlets which implement the <code>org.apache.catalina.CometProcessor</code>

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interface will have their event method invoked rather than the usual service

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method, according to the event which occurred. The event object gives

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access to the usual request and response objects, which may be used in the

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usual way. The main difference is that those objects remain valid and fully

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functional at any time between processing of the BEGIN event until processing

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an END or ERROR event.

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The following event types exist:

</p>

<ul>

<li>EventType.BEGIN: will be called at the beginning

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of the processing of the connection. It can be used to initialize any relevant

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fields using the request and response objects. Between the end of the processing

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of this event, and the beginning of the processing of the end or error events,

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it is possible to use the response object to write data on the open connection.

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Note that the response object and dependent OutputStream and Writer are still

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not synchronized, so when they are accessed by multiple threads,

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synchronization is mandatory. After processing the initial event, the request

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is considered to be committed.</li>

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<li>EventType.READ: This indicates that input data is available, and that one read can be made

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without blocking. The available and ready methods of the InputStream or

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Reader may be used to determine if there is a risk of blocking: the servlet

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should read while data is reported available. When encountering a read error,

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the servlet should report it by propagating the exception properly. Throwing

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an exception will cause the error event to be invoked, and the connection

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will be closed.

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Alternately, it is also possible to catch any exception, perform clean up

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on any data structure the servlet may be using, and using the close method

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of the event. It is not allowed to attempt reading data from the request

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object outside of the execution of this method.<br>

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On some platforms, like Windows, a client disconnect is indicated by a READ event.

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Reading from the stream may result in -1, an IOException or an EOFException.

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Make sure you properly handle all these three cases.

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If you don't catch the IOException, Tomcat will instantly invoke your event chain with an ERROR as

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it catches the error for you, and you will be notified of the error at that time.

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</li>

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<li>EventType.END: End may be called to end the processing of the request. Fields that have

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been initialized in the begin method should be reset. After this event has

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been processed, the request and response objects, as well as all their dependent

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objects will be recycled and used to process other requests. End will also be

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called when data is available and the end of file is reached on the request input

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(this usually indicates the client has pipelined a request).</li>

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<li>EventType.ERROR: Error will be called by the container in the case where an IO exception

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or a similar unrecoverable error occurs on the connection. Fields that have

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been initialized in the begin method should be reset. After this event has

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been processed, the request and response objects, as well as all their dependent

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objects will be recycled and used to process other requests.</li>

</ul>

<p>

There are some event subtypes which allow finer processing of events (note: some of these

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events require usage of the org.apache.catalina.valves.CometConnectionManagerValve valve):

</p>

<ul>

<li>EventSubType.TIMEOUT: The connection timed out (sub type of ERROR); note that this ERROR

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type is not fatal, and the connection will not be closed unless the servlet uses the close

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method of the event.

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</li>

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<li>EventSubType.CLIENT_DISCONNECT: The client connection was closed (sub type of ERROR).

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</li>

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<li>EventSubType.IOEXCEPTION: An IO exception occurred, such as invalid content, for example,

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an invalid chunk block (sub type of ERROR).

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</li>

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<li>EventSubType.WEBAPP_RELOAD: The web application is being reloaded (sub type of END).

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</li>

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<li>EventSubType.SESSION_END: The servlet ended the session (sub type of END).

</li>

</ul>

<p>

As described above, the typical lifecycle of a Comet request will consist in a series of

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events such as: BEGIN -> READ -> READ -> READ -> ERROR/TIMEOUT. At any time, the servlet

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may end processing of the request by using the close method of the event object.

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</p>

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</blockquote></td></tr></table>

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<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="CometFilter"><strong>CometFilter</strong></a></font></td></tr><tr><td><blockquote>

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<p>

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Similar to regular filters, a filter chain is invoked when comet events are processed.

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These filters should implement the CometFilter interface (which works in the same way as

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the regular Filter interface), and should be declared and mapped in the deployment

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descriptor in the same way as a regular filter. The filter chain when processing an event

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will only include filters which match all the usual mapping rules, and also implement

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the CometFiler interface.

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</p>

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</blockquote></td></tr></table>

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<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Example code"></a><a name="Example_code"><strong>Example code</strong></a></font></td></tr><tr><td><blockquote>

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<p>

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The following pseudo code servlet implements asynchronous chat functionality using the API

described above:

</p>

public class ChatServlet

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extends HttpServlet implements CometProcessor {

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protected ArrayList<HttpServletResponse> connections =

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new ArrayList<HttpServletResponse>();

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protected MessageSender messageSender = null;

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public void init() throws ServletException {

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messageSender = new MessageSender();

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Thread messageSenderThread =

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new Thread(messageSender, "MessageSender[" + getServletContext().getContextPath() + "]");

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messageSenderThread.setDaemon(true);

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messageSenderThread.start();

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}

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public void destroy() {

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connections.clear();

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messageSender.stop();

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messageSender = null;

}

/**

* Process the given Comet event.

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*

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* @param event The Comet event that will be processed

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* @throws IOException

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* @throws ServletException

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*/

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public void event(CometEvent event)

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throws IOException, ServletException {

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HttpServletRequest request = event.getHttpServletRequest();

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HttpServletResponse response = event.getHttpServletResponse();

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if (event.getEventType() == CometEvent.EventType.BEGIN) {

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log("Begin for session: " + request.getSession(true).getId());

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PrintWriter writer = response.getWriter();

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writer.println("<!doctype html public \"-//w3c//dtd html 4.0 transitional//en\">");

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writer.println("<head><title>JSP Chat</title></head><body bgcolor=\"#FFFFFF\">");

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writer.flush();

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synchronized(connections) {

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connections.add(response);

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}

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} else if (event.getEventType() == CometEvent.EventType.ERROR) {

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log("Error for session: " + request.getSession(true).getId());

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synchronized(connections) {

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connections.remove(response);

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}

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event.close();

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} else if (event.getEventType() == CometEvent.EventType.END) {

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log("End for session: " + request.getSession(true).getId());

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synchronized(connections) {

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connections.remove(response);

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}

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PrintWriter writer = response.getWriter();

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writer.println("</body></html>");

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event.close();

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} else if (event.getEventType() == CometEvent.EventType.READ) {

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InputStream is = request.getInputStream();

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byte[] buf = new byte[512];

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do {

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int n = is.read(buf); //can throw an IOException

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if (n > 0) {

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log("Read " + n + " bytes: " + new String(buf, 0, n)

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+ " for session: " + request.getSession(true).getId());

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} else if (n < 0) {

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error(event, request, response);

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return;

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}

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} while (is.available() > 0);

}

}

public class MessageSender implements Runnable {

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protected boolean running = true;

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protected ArrayList<String> messages = new ArrayList<String>();

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public MessageSender() {

}

public void stop() {

running = false;

}

/**

* Add message for sending.

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*/

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public void send(String user, String message) {

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synchronized (messages) {

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messages.add("[" + user + "]: " + message);

messages.notify();

}

}

public void run() {

while (running) {

if (messages.size() == 0) {

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try {

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synchronized (messages) {

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messages.wait();

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}

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} catch (InterruptedException e) {

// Ignore

}

}

synchronized (connections) {

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String[] pendingMessages = null;

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synchronized (messages) {

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pendingMessages = messages.toArray(new String[0]);

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messages.clear();

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}

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// Send any pending message on all the open connections

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for (int i = 0; i < connections.size(); i++) {

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try {

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PrintWriter writer = connections.get(i).getWriter();

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for (int j = 0; j < pendingMessages.length; j++) {

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writer.println(pendingMessages[j] + "<br>");

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}

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writer.flush();

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} catch (IOException e) {

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log("IOExeption sending message", e);

}

}

}

}

}

}

}

</pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>

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</blockquote></td></tr></table>

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<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Comet timeouts"></a><a name="Comet_timeouts"><strong>Comet timeouts</strong></a></font></td></tr><tr><td><blockquote>

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<p>If you are using the NIO connector, you can set individual timeouts for your different comet connections.

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To set a timeout, simply set a request attribute like the following code shows:

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<div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>CometEvent event.... event.setTimeout(30*1000);</pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div> or

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<div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>event.getHttpServletRequest().setAttribute("org.apache.tomcat.comet.timeout", new Integer(30 * 1000));</pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>

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This sets the timeout to 30 seconds.

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Important note: in order to set this timeout, it has to be done on the <code>BEGIN</code> event.

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The default value is <code>soTimeout</code>

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</p>

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<p>If you are using the APR connector, all Comet connections will have the same timeout value. It is <code>soTimeout*50</code>

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</p>

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</blockquote></td></tr></table>

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</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Asynchronous writes"></a><a name="Asynchronous_writes"><strong>Asynchronous writes</strong></a></font></td></tr><tr><td><blockquote>

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<p>

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When APR or NIO is enabled, Tomcat supports using sendfile to send large static files.

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These writes, as soon as the system load increases, will be performed

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asynchronously in the most efficient way. Instead of sending a large response using

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blocking writes, it is possible to write content to a static file, and write it

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using a sendfile code. A caching valve could take advantage of this to cache the

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response data in a file rather than store it in memory. Sendfile support is

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available if the request attribute <code>org.apache.tomcat.sendfile.support</code>

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is set to <code>Boolean.TRUE</code>.

</p>

<p>

Any servlet can instruct Tomcat to perform a sendfile call by setting the appropriate

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request attributes. It is also necessary to correctly set the content length

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for the response. When using sendfile, it is best to ensure that neither the

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request or response have been wrapped, since as the response body will be sent later

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by the connector itself, it cannot be filtered. Other than setting the 3 needed

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request attributes, the servlet should not send any response data, but it may use

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any method which will result in modifying the response header (like setting cookies).

</p>

<ul>

<li><code>org.apache.tomcat.sendfile.filename</code>: Canonical filename of the file which will be sent as

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a String</li>

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<li><code>org.apache.tomcat.sendfile.start</code>: Start offset as a Long</li>

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<li><code>org.apache.tomcat.sendfile.end</code>: End offset as a Long</li>

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</ul>

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</blockquote></td></tr></table></td></tr><tr><td colspan="2"><hr noshade="noshade" size="1"></td></tr><tr><td colspan="2"><div align="center"><font color="#525D76" size="-1"><em>

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</em></font></div></td></tr></table></body></html>