Tomcat 6支持的Comet

最新推荐文章于 2022-07-22 23:38:37 发布

最新推荐文章于 2022-07-22 23:38:37 发布 · 143 阅读

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#Comet #Tomcat #J# #JSP #thread

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本文介绍如何利用Tomcat6的新特性Comet技术来实现一个简单的聊天应用。通过Comet技术，开发者能够轻松地为Web应用添加推送功能。文章提供了一个具体的聊天Servlet实例，展示了如何处理连接、发送消息等操作。

今天在测试中无意中看到Tomcat 6的新特性Comet，使用Comet技术可以轻松实现一个Pushlet的功能，让我看了着实兴奋不已，而其官方网站还给出了一个Messenger的例子。

public class ChatServlet
extends HttpServlet implements CometProcessor {
protected ArrayList<HttpServletResponse> connections =
new ArrayList<HttpServletResponse> ( );
protected MessageSender messageSender = null;
public void init ( ) throws ServletException {
messageSender = new MessageSender ( );
Thread messageSenderThread =
new Thread (messageSender, "MessageSender[" + getServletContext ( ). getContextPath ( ) + "]" );
messageSenderThread. setDaemon ( true );
messageSenderThread. start ( );
}
public void destroy ( ) {
connections. clear ( );
messageSender. stop ( );
messageSender = null;
}
/**
* Process the given Comet event.
*
* @param event The Comet event that will be processed
* @throws IOException
* @throws ServletException
*/
public void event (CometEvent event )
throws IOException, ServletException {
HttpServletRequest request = event. getHttpServletRequest ( );
HttpServletResponse response = event. getHttpServletResponse ( );
if (event. getEventType ( ) == CometEvent. EventType. BEGIN ) {
log ( "Begin for session: " + request. getSession ( true ). getId ( ) );
PrintWriter writer = response. getWriter ( );
writer. println ( "<!doctype html public \"-//w3c//dtd html 4.0 transitional//en\">" );
writer. println ( "<head><title>JSP Chat</title></head><body bgcolor=\"#FFFFFF\">" );
writer. flush ( );
synchronized (connections ) {
connections. add (response );
}
} else if (event. getEventType ( ) == CometEvent. EventType. ERROR ) {
log ( "Error for session: " + request. getSession ( true ). getId ( ) );
synchronized (connections ) {
connections. remove (response );
}
event. close ( );
} else if (event. getEventType ( ) == CometEvent. EventType. END ) {
log ( "End for session: " + request. getSession ( true ). getId ( ) );
synchronized (connections ) {
connections. remove (response );
}
PrintWriter writer = response. getWriter ( );
writer. println ( "</body></html>" );
event. close ( );
} else if (event. getEventType ( ) == CometEvent. EventType. READ ) {
InputStream is = request. getInputStream ( );
byte [ ] buf = new byte [ 512 ];
do {
int n = is. read (buf ); //can throw an IOException
if (n > 0 ) {
log ( "Read " + n + " bytes: " + new String (buf, 0, n )
+ " for session: " + request. getSession ( true ). getId ( ) );
} else if (n < 0 ) {
error (event, request, response );
return;
}
} while (is. available ( ) > 0 );
}
}
public class MessageSender implements Runnable {
protected boolean running = true;
protected ArrayList<String> messages = new ArrayList<String> ( );
public MessageSender ( ) {
}
public void stop ( ) {
running = false;
}
/**
* Add message for sending.
*/
public void send ( String user, String message ) {
synchronized (messages ) {
messages. add ( "[" + user + "]: " + message );
messages. notify ( );
}
}
public void run ( ) {
while (running ) {
if (messages. size ( ) == 0 ) {
try {
synchronized (messages ) {
messages. wait ( );
}
} catch ( InterruptedException e ) {
// Ignore
}
}
synchronized (connections ) {
String [ ] pendingMessages = null;
synchronized (messages ) {
pendingMessages = messages. toArray ( new String [ 0 ] );
messages. clear ( );
}
// Send any pending message on all the open connections
for ( int i = 0; i < connections. size ( ); i++ ) {
try {
PrintWriter writer = connections. get (i ). getWriter ( );
for ( int j = 0; j < pendingMessages. length; j++ ) {
writer. println (pendingMessages [j ] + "<br>" );
}
writer. flush ( );
} catch ( IOException e ) {
log ( "IOExeption sending message", e );
}
}
}
}
}
}
}

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