注意一：
@WebServlet(urlPatterns={"/hi"},asyncSupported=true)
注意二：
在客户端看来， 这仍然是同步的请求， 客户端需要等待请求结果。
注意三：异步分为请求异步和相应异步， 本例子只是响应方法异步。
/**
* Copyright (c) 2014 Oracle and/or its affiliates. All rights reserved.
*
* You may not modify, use, reproduce, or distribute this software except in
* compliance with the terms of the License at:
* http://java.net/projects/javaeetutorial/pages/BerkeleyLicense
*/
package javaeetutorial.hello2;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.AsyncContext;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* This is a simple example of an HTTP Servlet. It responds to the GET method of
* the HTTP protocol.
*/
@WebServlet(urlPatterns={"/hi"},asyncSupported=true)
public class GreetingServlet extends HttpServlet {
@Override
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
final AsyncContext context= request.startAsync();
context.start(new Runnable(){
@Override
public void run() {
try {
Thread.sleep(10000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
// then write the data of the response
try {
context.getResponse().getWriter().println("hello");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
context.complete();
}
});
}
@Override
public String getServletInfo() {
return "The Hello servlet says hello.";
}
}