Java Servlet 3.0 异步支持实例

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Servlet 3.0中包含了一些重要的新特性。其中包含异步支持。 在这里,我们将看到如何配置一个异步的servlet。

Objective:

  • How to code Java Async Servlet?

Environment & Tools:

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

Library:

  • Java Servlet API 3.0

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.

索引.png

( 3 ) Run Sample Code

Using Maven we can run this sample code as following:

>mvn jetty:run

 Souce Code @ GitHub

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