Servlet3.0之异步支持

理解异步请求在Servlet中的实现

最新推荐文章于 2025-11-30 18:24:05 发布

最新推荐文章于 2025-11-30 18:24:05 发布 · 189 阅读

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#java #servlet3.0 #异步

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本文详细解释了在Servlet中使用异步请求的概念、关键接口和监听器的运用，通过实例展示了如何在Servlet中引入异步操作，并在主线程和子线程间高效交互。了解如何利用异步请求提高用户体验和服务器效率。

将该部分单独拧出来，方便查看

3.3 异步的支持

3.3.1 AsyncContext接口

ServletRequest执行startAsync()或者startAsync(ServletRequest, ServletResponse) 进入异步模式，将会创建一个AsyncContext，将其需要异步的操作放在此AsyncContext中

addListener(AsyncListener listener)//可以增加监听器

3.3.2 ServletRequest接口

startAsync()

startAsync(ServletRequest, ServletResponse)

将当前请求/响应或指定请求/响应放到异步模式中

3.3.3 AsyncListener异步监听器

void	onComplete`(`AsyncEvent `event)` Notifies this AsyncListener that an asynchronous operation has been completed.
`void`	onError`(`AsyncEvent `event)` Notifies this AsyncListener that an asynchronous operation has failed to complete.
`void`	onStartAsync`(`AsyncEvent `event)` Notifies this AsyncListener that a new asynchronous cycle is being initiated via a call to one of the `ServletRequest#startAsync` methods.
`void`	onTimeout`(`AsyncEvent `event)` Notifies this AsyncListener that an asynchronous operation has timed out.

可以给AsyncContext实例增加一个AsyncListener监听器，当AsyncContext调用complete()完成后即可触发onComplete(e)方法

3.3.4 例子

asyncSupported要定义为true

3.3.4.1简单例子

@WebServlet(name = "syncServlet", value = { "/syncServlet"},asyncSupported=true)

publicclass SyncTestServlet extends HttpServlet {

privatestaticfinallongserialVersionUID = -126107068129496624L;

publicvoid doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

response.setContentType("text/html");

PrintWriter out = response.getWriter();

out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");

out.println("<HTML>");

out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");

out.println(" <BODY>");

out.print(" Servlet Start::: This is ");

out.print(this.getClass());

out.println(" using the GET method ");

out.flush();

//-------------增加一个异步线程

System.out.println("主response对象:"+response);

AsyncContext sc = request.startAsync(request,response);

Thread t = new Thread(new MyThread(sc));

t.start();

//-------------继续主线程

//注：主线程不需要等待子线程完毕，可以先执行并打印出来【异步进行】

out.println(" -------Servlet end.");

out.flush();

}

class MyThread extends Thread{

private AsyncContext syncContext;

public MyThread(AsyncContext syncContext){

this.syncContext = syncContext;

}

publicvoid run(){

System.out.println("MyThread start2....");

HttpServletResponse resp = (HttpServletResponse) syncContext.getResponse();

System.out.println("MyThread end2....");

try {

PrintWriter out = resp.getWriter();

out.println(" -----MyThread start----");

out.println(" -----wait running.....");

out.flush();//flush即可先输出，不需要等全部完成

System.out.println("子线程里的response对象（和主线程是同一个）:"+resp);

Thread.sleep(3000);

out.println(" -----MyThread end----");

out.println(" </BODY>");

out.println("</HTML>");

out.flush();

//out.close();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (InterruptedException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

syncContext.complete();//完成异步操作

}

Servlet3.0之异步支持

将该部分单独拧出来，方便查看

3.3 异步的支持

3.3.1 AsyncContext接口

3.3.2 ServletRequest接口

3.3.3 AsyncListener异步监听器

3.3.4 例子

3.3.4.1简单例子

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