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POJava Servlets: why is PrintWriter.flush() not flushing?
 

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    <p>I am currently writing a Comet application which requires me to send chunks of data at a time on a persistent connection. However, I'm having trouble flushing the message to the client before closing the connection. Is there any reason the PrintWriter.flush() method is not behaving like I think it should?</p> <p>This is my Tomcat Comet implementation:</p> <pre><code>public void event(CometEvent event) throws IOException, ServletException { HttpServletRequest request = event.getHttpServletRequest(); HttpServletResponse response = event.getHttpServletResponse(); if (event.getEventType() == EventType.BEGIN) { request.setAttribute("org.apache.tomcat.comet.timeout", 300 * 1000); PrintWriter out = response.getWriter(); out.println("BEGIN!"); out.flush(); System.out.println("EventType.BEGIN"); } else if (event.getEventType() == EventType.READ) { InputStream is = request.getInputStream(); byte[] buf = new byte[512]; do { int n = is.read(buf); //can throw an IOException if (n &gt; 0) { System.out.println("Read " + n + " bytes: " + new String(buf, 0, n) + " for session: " + request.getSession(true).getId()); } else if (n &lt; 0) { return; } } while (is.available() &gt; 0); System.out.println("subtype: "+event.getEventSubType()); System.out.println("EventType.READ"); } else if (event.getEventType() == EventType.END) { PrintWriter out = response.getWriter(); out.println("END!"); out.close(); System.out.println("checkError: "+out.checkError()); System.out.println(event.getEventSubType()); System.out.println("EventType.END"); //eventWorker.enqueue(new EndEvent(request, response)); } else if (event.getEventType() == EventType.ERROR) { PrintWriter out = response.getWriter(); out.println("ERROR!"); out.flush(); System.out.println("checkError: "+out.checkError()); System.out.println("subtype: "+event.getEventSubType()); //response.getWriter().close(); System.out.println("EventType.ERROR"); } else { (new ServletException("EXCEPTION")).printStackTrace(); } } </code></pre> <p>So here I'm trying to send the message "BEGIN!" and keep the connection open afterwards so I can send more data. However, it seems that the message doesn't go through until the connection is closed.</p> <p>This is my ajax code: $.post('comet', function(data) { alert(data); }); </p> <p>After I run this code, Firebug tells me that this is the response header: Server: Apache-Coyote/1.1 Transfer-Encoding: chunked Date: Mon, 13 Jul 2009 21:16:29 GMT</p> <p>This leads me to think that my browser received some data back, but how do I update something on the page before the connection is closed?</p>
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