Servlet 3 Async task on Tomcat 7

Question

I\'m trying to implement Simple chat using Servlet 3.0 and Comet pattern based on its async support.

I\'m inspired by this article: http://www.javaworld.com/javaworld/jw

Answer 1

I can't comment on Ramesh's code, so I have to place it here... Since no thread wraps round the ChatManager runnable, I believe you should call run() on it and not start(). Also, quite obvious though, it should be new ChatManager()..not new chatManager()...account of Java been case-sensitive.

Answer 2

You are running while loop inside contextInitialized() method which is wrong. contextInitialized() is invoked by Servlet Container as part of the application startup, having while loop there will block your app start.

Modified the code such the ContextListener will start one daemon thread which publishes the messages to the watchers

@WebListener
public class ChatPushService implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
          final List<AsyncContext> watchers = new  ArrayList<AsyncContext>();
         sce.getServletContext().setAttribute("watchers", watchers);
          // store new messages not published yet
         Queue<String> messages = new ConcurrentLinkedQueue<String>();
         sce.getServletContext().setAttribute("messages", messages);
         new chatManager(sce.getServletContext()).start(); //START DAEMON

      }
}
public class ChatManager implements Runnable
{
ServletContext servletCtx;
public ChatManager(ServletContext ctx)
{
     this.servletCtx = ctx;
}
public void run()
{
         List<AsyncContext> watchers = (List<AsyncContext>) servletCtx.getAttribute("watchers");
     Queue<String> messages = (Queue<String>)appScope.getAttribute("messages");
     Executor messageExecutor = Executors.newCachedThreadPool(); 
         final Executor watcherExecutor = Executors.newCachedThreadPool();
         while(true)
          {      

             if(!messages.isEmpty()) 
             {
                 System.out.println("notEmpty");
                String message =  messages.poll(); 
                messageExecutor.execute(new Runnable(){

                    @Override
                    public void run() {
                         for(final AsyncContext aCtx : watchers){
                             watcherExecutor.execute(new Runnable(){

                                 @Override
                                    public void run() {
                                       try {
                                        aCtx.getResponse().getWriter().print("brrrrr");
                                    } catch (IOException e) {
                                        // TODO Auto-generated catch block
                                        e.printStackTrace();
                                    }
                                 }
                             });
                         }
                    }
             });
          }
    }

}

}