关于servlet3.0中的异步servlet

 刚看了一下维基百科上的介绍,servlet3.0是2009年随着JavaEE6.0发布的:

到现在已经有六七年的时间了,在我第一次接触java的时候(2011年),servlet3.0就已经出现很久了,但是到现在,里边的一些东西还是没有能够好好地了解一下

最近在研究java的长连接,在了解jetty中的continuations机制的时候也重新了解了一下servlet3.0中的异步servlet机制,通过看几个博客,加上自己的一些测试,算是搞明白了一些,在这里记录一下:

在服务器的并发请求数量比较大的时候,会产生很多的servlet线程(这些servlet线程在servlet容器的线程池中维护),如果每个请求需要耗费的时间比较长(比如,执行了一些IO的处理等),在之前的非异步的servlet中,这些servlet线程将会阻塞,严重耗费服务器的资源.而在servlet3.0中首次出现的异步servlet,通过一个单独的新的线程来执行这些比较耗时的任务(也可以把这些任务放到一个自己维护的线程池里),servlet线程立即返回servlet容器的servlet池以便响应其他请求,这样,在降低了系统的资源消耗的同时,也会提升系统的吞吐量

下面是我自己做的一个模拟的操作(代码参考了importnew上的这篇文章:http://www.importnew.com/8864.html)

一个服务器端需要十秒才能返回的servlet,分别有同步的版本和异步的版本,通过JMeter做压力测试,配合jprofiler来分析服务器的资源消耗情况(主要是线程的创建和使用情况)来分析当服务器处理时间较长的时候,异步的servlet和同步的servlet对服务器性能的影响

同步的servlet:

package com.jiaoyiping.websample.asyncServlet;
 /*
  * Created with Intellij IDEA
  * USER: 焦一平
  * Mail: jiaoyiping@gmail.com
  * Date: 2016/10/22
  * Time: 22:16
  * To change this template use File | Settings | Editor | File and Code Templates
 */
import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

import java.io.PrintWriter;
@WebServlet(urlPatterns = "/syncServlet")

public class SyncServlet extends HttpServlet {

//线程睡眠十秒才返回的servlet

private static final long serialVersionUID = 1L;
</span><span style="color: #0000ff;">protected</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> doGet(HttpServletRequest request,
                     HttpServletResponse response) </span><span style="color: #0000ff;">throws</span><span style="color: #000000;"> ServletException, IOException {
    </span><span style="color: #0000ff;">long</span> startTime =<span style="color: #000000;"> System.currentTimeMillis();
    System.out.println(</span>"LongRunningServlet Start::Name="
            + Thread.currentThread().getName() + "::ID="
            +<span style="color: #000000;"> Thread.currentThread().getId());
    </span><span style="color: #0000ff;">int</span> milliseconds = 10000<span style="color: #000000;">;
    longProcessing(milliseconds);

    PrintWriter out </span>=<span style="color: #000000;"> response.getWriter();
    </span><span style="color: #0000ff;">long</span> endTime =<span style="color: #000000;"> System.currentTimeMillis();
    out.write(</span>"Processing done for " + milliseconds + " milliseconds!!"<span style="color: #000000;">);
    System.out.println(</span>"LongRunningServlet Start::Name="
            + Thread.currentThread().getName() + "::ID="
            + Thread.currentThread().getId() + "::Time Taken="
            + (endTime - startTime) + " ms."<span style="color: #000000;">);
    out.flush();
    out.close();
}

</span><span style="color: #0000ff;">private</span> <span style="color: #0000ff;">void</span> longProcessing(<span style="color: #0000ff;">int</span><span style="color: #000000;"> secs) {
    </span><span style="color: #0000ff;">try</span><span style="color: #000000;"> {
        Thread.sleep(secs);
    } </span><span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) {
        e.printStackTrace();
    }
}

}    

异步的servlet:

package com.jiaoyiping.websample.asyncServlet.async;
import javax.servlet.AsyncContext;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

import java.util.concurrent.ThreadPoolExecutor;
/*


Created with Intellij IDEA


USER: 焦一平


Mail: jiaoyiping@gmail.com


Date: 2016/10/22


Time: 22:38


To change this template use File | Settings | Editor | File and Code Templates

*/

@WebServlet(asyncSupported = true, urlPatterns = "/asyncServlet")

public class AsyncServlet extends HttpServlet {

@Override

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

long startTime = System.currentTimeMillis();

System.out.println("AsyncLongRunningServlet Start::Name="

+ Thread.currentThread().getName() + "::ID="

+ Thread.currentThread().getId());
request.setAttribute(</span>"org.apache.catalina.ASYNC_SUPPORTED", <span style="color: #0000ff;">true</span><span style="color: #000000;">);
</span><span style="color: #0000ff;">int</span> secs = 10000<span style="color: #000000;">;
AsyncContext asyncCtx </span>=<span style="color: #000000;"> request.startAsync();
asyncCtx.addListener(</span><span style="color: #0000ff;">new</span><span style="color: #000000;"> AppAsyncListener());
asyncCtx.setTimeout(</span>2000000<span style="color: #000000;">);
ThreadPoolExecutor executor </span>= (ThreadPoolExecutor) request.getServletContext().getAttribute("executor"<span style="color: #000000;">);
executor.execute(</span><span style="color: #0000ff;">new</span><span style="color: #000000;"> AsyncRequestProcessor(asyncCtx, secs));
</span><span style="color: #0000ff;">long</span> endTime =<span style="color: #000000;"> System.currentTimeMillis();
System.out.println(</span>"AsyncLongRunningServlet End::Name="
        + Thread.currentThread().getName() + "::ID="
        + Thread.currentThread().getId() + "::Time Taken="
        + (endTime - startTime) + " ms."<span style="color: #000000;">);

}

}