313 lines
20 KiB
HTML
313 lines
20 KiB
HTML
<html><head><META http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>Apache Tomcat 6.0 - Advanced IO and Tomcat</title><meta name="author" value="Remy Maucherat"><meta name="email" value=""></head><body bgcolor="#ffffff" text="#000000" link="#525D76" alink="#525D76" vlink="#525D76"><table border="0" width="100%" cellspacing="0"><!--PAGE HEADER--><tr><td><!--PROJECT LOGO--><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><font face="arial,helvetica,sanserif"><h1>Apache Tomcat 6.0</h1></font></td><td><!--APACHE LOGO--><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"><!--HEADER SEPARATOR--><tr><td colspan="2"><hr noshade="noshade" size="1"></td></tr><tr><!--RIGHT SIDE MAIN BODY--><td width="80%" valign="top" align="left"><table border="0" width="100%" cellspacing="4"><tr><td align="left" valign="top"><h1>Apache Tomcat 6.0</h1><h2>Advanced IO and Tomcat</h2></td><td align="right" valign="top" nowrap="true"><img src="./../images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></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.
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</p>
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<p>
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<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"><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 aynchronously, recieving
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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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asychnonously (most likely responding to some event raised from some
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other source).
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</p>
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<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:
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</p>
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<ul>
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<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 depedent 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, and can make one additional read
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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>
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</ul>
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<p>
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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):
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</p>
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<ul>
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<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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method of the event.
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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).
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</li>
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</ul>
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<p>
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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"><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 implments asynchronous chat functionality using the API
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described above:
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</p>
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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" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./../images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./../images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./../images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
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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;
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}
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/**
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* 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);
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}
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}
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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() {
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}
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public void stop() {
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running = false;
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}
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/**
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* 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);
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messages.notify();
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}
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}
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public void run() {
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while (running) {
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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) {
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// Ignore
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}
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}
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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);
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}
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}
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}
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}
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}
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}
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}
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</pre></td><td bgcolor="#023264" width="1"><img src="./../images/void.gif" 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" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./../images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./../images/void.gif" 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"><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, simple 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" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./../images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./../images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./../images/void.gif" 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" 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" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./../images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./../images/void.gif" 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" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./../images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./../images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./../images/void.gif" 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" 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" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./../images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./../images/void.gif" 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"><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>.
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</p>
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<p>
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Any servlet can instruct Tomcat to perform a sendfile call by setting the appropriate
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response attributes. 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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response 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).
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</p>
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<ul>
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<li>org.apache.tomcat.sendfile.filename: Canonical filename of the file which will be sent as
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a String</li>
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<li>org.apache.tomcat.sendfile.start: Start offset as a Long</li>
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<li>org.apache.tomcat.sendfile.start: End offset as a Long</li>
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</ul>
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</blockquote></td></tr></table></td></tr><!--FOOTER SEPARATOR--><tr><td colspan="2"><hr noshade="noshade" size="1"></td></tr><!--PAGE FOOTER--><tr><td colspan="2"><div align="center"><font color="#525D76" size="-1"><em>
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Copyright © 1999-2006, Apache Software Foundation
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</em></font></div></td></tr></table></body></html> |