将数据从Servlet Java发送到JSP

Question

I'm doing a project in java in which I implemented a chat, everything works perfectly only when I receive messages I can not print the web page. In my Servlet I have a callback method that is invoked when messages arrive, in fact if you see mold them in the console, but if you are sending them to the jsp using the RequestDispatcher can not get them to see.

I would like to know if there is a system that the jsp page listens for a callback method in the servlet?

Obviously, this system should not be constantly invoke the class I have something absurd like that.

So that I can print the messages I receive.

---

This is my code I put a comment where I should print eventually find in jsp page, or do a redirect by passing parameters post or get

     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


    String strJid = (String) request.getParameter("jid");
    String strMessage = (String) request.getParameter("textMessage");


    Connection connection = (Connection)getServletContext().getAttribute("classConnection");

    ChatManager chatManager = connection.getChatManager();
    Chat newChat = chatManager.createChat(strJid, new MessageListener(){


        @Override
        public void processMessage(Chat chat, Message message){

     //from here I have to print the message.getBody () in jsp page,
    //how can I do? I'm happy also reload the page and pass as a parameter to get or post

        }
    });

    try{
        newChat.sendMessage(strMessage);
    }
    catch(XMPPException e){
        System.out.println("Errore invio messaggio");
    }


}

Answer 1

To implement a callback method in your servlet to receive chat messages is the wrong approach. A servlet will be called once for a browser request, creates the HTML page and send it back to the browser. After that there is no such kind of a connection between the servlet and the web page.

In traditional web programming all communication between browser and server is intiated by the client. There is no way for the server to send a message to the client. Workarounds are long polling requests.

But nowadays you can use Websockets . There are several frameworks supporting Websockets both for client and server side. One of them is Atmosphere . Their tutorial is a chat application.