Servlet3.0之后版本使用Servlet的异步处理

在实际开发中，如果Servlet接收的请求是需要操作IO流然后再通过IO流的结果来访问或者更新数据库的，那么这个耗时的操作就要放在异步中处理，然后Servlet先跳到一个等待页面，在这个页面中通过Ajax不断发送请求读取异步处理的结果，这样用户体验会比较好，那么Servlet实现异步处理只需要使用到Servlet3.0之后提供的AsyncContext对象，简单的使用方法如下：

@WebServlet(name = "AcyncServlet", urlPatterns = "/AcyncServletDemo", asyncSupported = true)
public class AcyncServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");

        PrintWriter out = response.getWriter();
        out.println("<h1>Servlet Do Post Start</h1>");
        out.flush();

        AsyncContext context = request.startAsync();
        //开启线程
        new AsyncThread(context).start();

        out.println("<h1>Servlet Do Post End</h1>");
        out.flush();
    }

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

    class AsyncThread extends Thread {
        private AsyncContext context;

        public AsyncThread(AsyncContext context) {
            this.context = context;
        }

        @Override
        public void run() {
            try {
                Thread.sleep(2000);
                PrintWriter out = context.getResponse().getWriter();
                out.println("<h1>异步延时输出，这里可以进行一些耗时的操作</h1>");
                out.flush();
                context.complete();

            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

}

在这里，我在注释配置中配置了想要的url-pattern，所以就不需要在web.xml中再次进行配置：

@WebServlet(name = "AcyncServlet", urlPatterns = "/AcyncServletDemo", asyncSupported = true)

要注意的是，必须设置

asyncSupported = true

<h1>Servlet Do Post Start</h1>