Java Servlet 3.0 異步支持實例

Servlet 3.0中包含了一些重要的新特性。其中包含異步支持。 在這里，我們將看到如何配置一個異步的servlet。

Objective:

• How to code Java Async Servlet?
</ul>

Environment & Tools:

• JDK 1.7
• Eclipse (or other IDE)
• Maven (optional)
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Library:

• Java Servlet API 3.0
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This Sample:
We will send 5 jquery.ajax request to the async servlet. These requests will run 5 threads that will stay on hold until we send a request with “exit” parameter.

( 1 ) Async Servlet

We will use @WebServlet to define the servlet instead of using web.xml file.

package com.hmkcode;

import java.io.IOException;

import javax.servlet.AsyncContext;
import javax.servlet.AsyncEvent;
import javax.servlet.AsyncListener;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(name="asyncServlet",value = {"/async"},asyncSupported = true)
public class AsyncServlet extends HttpServlet
{

private static final long serialVersionUID = 1L;

    String param ="";

  @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {

       // 1.0 start async
       final AsyncContext ctx = req.startAsync();
       param = ctx.getRequest().getParameter("seq");

       // 2.0 set the timeout
       ctx.setTimeout(0);

       // 3.0 add listener
       ctx.addListener(new AsyncListener() {

            @Override
            public void onTimeout(AsyncEvent arg0) throws IOException {
                System.out.println("onTimeout...");            
            }

            @Override
            public void onStartAsync(AsyncEvent arg0) throws IOException {
                System.out.println("onStartAsync...");             
            }

            @Override
            public void onError(AsyncEvent arg0) throws IOException {
                System.out.println("onError...");          
            }

            @Override
            public void onComplete(AsyncEvent arg0) throws IOException {
                System.out.println("onComplete...");
            }
       });

       // 4.0 run a thread
       ctx.start(new Runnable() {
            @Override
            public void run() {
                 try {

                      // hold until receive exit
                      while(!param.equals("exit")){}

                      ctx.getResponse().getWriter().write(ctx.getRequest().getParameter("seq"));

                } catch (IOException e) {
                    e.printStackTrace();
                }

             ctx.complete();
            }

       });
   }
}

We need 4 steps to make our async servlet.

1. Get AsyncContext
2. Set TimeOut (optional)
3. Add Listener
4. Call AsyncContext.start()

 ( 2 ) Client Side

This part is just providing a way to send some request to the async servlet.

• index.html
• myfunctions.js



( 3 ) Run Sample Code

Using Maven we can run this sample code as following:

>mvn jetty:run

 Souce Code @ GitHub