spring mvc对异步请求的处理

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在spring mvc3.2及以上版本增加了对请求的异步处理，是在servlet3的基础上进行封装的。

1、修改web.xml

<?xml version="1.0" encoding="UTF-8"?><web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee"    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee     http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">...</web-app>

1.1、声明version="3.0"，声明web-app_3_0.xsd

1.2、为servlet或者filter设置启用异步支持：<async-supported>true</async-supported>，修改WEB应用的web.xml

<!-- spring mvc --><servlet><servlet-name>SpringMvc</servlet-name><servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class><init-param><param-name>contextConfigLocation</param-name><param-value>...</param-value></init-param><load-on-startup>1</load-on-startup><async-supported>true</async-supported></servlet>

2、使controller类支持async

2.1、返回java.util.concurrent.Callable来完成异步处理

package org.springframework.samples.mvc.async;  import java.util.concurrent.Callable;  import org.springframework.stereotype.Controller;import org.springframework.ui.Model;import org.springframework.web.bind.annotation.ExceptionHandler;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RequestParam;import org.springframework.web.bind.annotation.ResponseBody;import org.springframework.web.context.request.async.WebAsyncTask;  @Controller@RequestMapping("/async/callable")public class CallableController {    @RequestMapping("/response-body")    public @ResponseBody Callable<String> callable() {          return new Callable<String>() {            @Override            public String call() throws Exception {                Thread.sleep(2000);                return "Callable result";            }        };    }      @RequestMapping("/view")    public Callable<String> callableWithView(final Model model) {          return new Callable<String>() {            @Override            public String call() throws Exception {                Thread.sleep(2000);                model.addAttribute("foo", "bar");                model.addAttribute("fruit", "apple");                return "views/html";            }        };    }      @RequestMapping("/exception")    public @ResponseBody Callable<String> callableWithException(            final @RequestParam(required=false, defaultValue="true") boolean handled) {          return new Callable<String>() {            @Override            public String call() throws Exception {                Thread.sleep(2000);                if (handled) {                    // see handleException method further below                    throw new IllegalStateException("Callable error");                }                else {                    throw new IllegalArgumentException("Callable error");                }            }        };    }      @RequestMapping("/custom-timeout-handling")    public @ResponseBody WebAsyncTask<String> callableWithCustomTimeoutHandling() {          Callable<String> callable = new Callable<String>() {            @Override            public String call() throws Exception {                Thread.sleep(2000);                return "Callable result";            }        };          return new WebAsyncTask<String>(1000, callable);    }      @ExceptionHandler    @ResponseBody    public String handleException(IllegalStateException ex) {        return "Handled exception: " + ex.getMessage();    }  }

2.2、在异步处理完成时返回org.springframework.web.context.request.async.DeferredResult其他线程，例如一个JMS或一个AMQP消息,Redis通知等等：

@RequestMapping("/quotes")@ResponseBodypublic DeferredResult<String> quotes() {  DeferredResult<String> deferredResult = new DeferredResult<String>();  // Add deferredResult to a Queue or a Map...  return deferredResult;}    // In some other thread...deferredResult.setResult(data);// Remove deferredResult from the Queue or Map

3、spring配置文件的修改

spring mvc的dtd的声明必须大于等于3.2

<mvc:annotation-driven><!--  可不设置，使用默认的超时时间 -->    <mvc:async-support default-timeout="3000"/></mvc:annotation-driven>

实际使用示例：

function deferred(){    $.get('quotes.htm',function(data){        console.log(data);        deferred();//每次请求完成,再发一次请求,避免客户端定时刷新来获取数据    });}

这么做的好处避免web server的连接池被长期占用而引起性能问题，调用后生成一个非web的服务线程来处理，增加web服务器的吞吐量~~

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