JavaEE6-异步Servlet Sample

最新推荐文章于 2023-03-29 17:47:02 发布

karl1235

最新推荐文章于 2023-03-29 17:47:02 发布

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分类专栏： JavaEE

本文链接：https://blog.youkuaiyun.com/karl5421/article/details/10003731

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本文介绍了一个使用Java EE 6的异步Servlet示例，通过主线程启动子线程处理耗时任务，同时保持与客户端的连接。展示了如何配置AsyncContext并监听其状态变化。

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个人理解：

异步Servlet工作方式在主线程基础之上再新开一个子线程来处理比较耗时的任务，两个线程共用一个socket连接，所以在连接的关闭上需小心。

异步Servlet代码：

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package me.ypqiao.javaee6sample.listener;

import java.io.IOException;
import java.io.PrintWriter;
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;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 *
 * @author ypqiao
 */
@WebServlet(name = "AsynServlet", urlPatterns = {"/AsynServlet"}, 
        asyncSupported = true)
public class AsynServlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest request, 
            HttpServletResponse response) throws ServletException, IOException {
        
        request.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");
       
        PrintWriter out = response.getWriter();
        
        try {
         
            out.println(" work1 completed <br/>");
            
            // get and config an instance of AsyncContext
            AsyncContext ctx = request.startAsync();
            ctx.setTimeout(2000);
            ctx.addListener( new AsyncContextListener() );
            
            // start the asynccontext to do ayncwork
            ctx.start( new AsyncTask(ctx));
            
            out.println(" work3 completed  <br/>");
            
         
        } finally {            
            out.flush();
        }
    }
}

class AsyncTask implements Runnable {
    
    private static Log log = LogFactory.getLog(AsyncTask.class);
    
    private AsyncContext context;

    public AsyncTask(AsyncContext context){
        this.context = context;
    }
    
    @Override
    public void run() {
        
        log.info(" start to do a long-time work ");
        
        try {
            
            Thread.sleep(2000);
            context.getResponse().getWriter().print(" work2 completed  <br/>");
            
            //throw new RuntimeException(" exception test ");
            
        }
        catch( Exception e ){
            log.error(e.getMessage(),e);
        }
        finally{
             context.complete();
        }
    }
}


class AsyncContextListener implements AsyncListener{

    private static Log log = LogFactory.getLog(AsyncContextListener.class);
        
    @Override
    public void onComplete(AsyncEvent event) throws IOException {
        log.info(" the asyn context has been completed ");
    }

    @Override
    public void onTimeout(AsyncEvent event) throws IOException {
       
        log.warn(" the asyn context has been timeout ");
        
    }

    @Override
    public void onError(AsyncEvent event) throws IOException {
        
        log.error(" the asyn context has error ",event.getThrowable());
        
    }

    @Override
    public void onStartAsync(AsyncEvent event) throws IOException {
        
        log.debug(" the asyn context has started ",event.getThrowable());
        
    }
    
}