详解spring mvc对异步请求的处理

详解spring mvc对异步请求的处理

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

xmlns:xsi="http://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">

...

xmlns:xsi="http://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">

...

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： true ，修改WEB应用的web.xml

SpringMvc

org.springframework.web.servlet.DispatcherServlet

contextConfigLocation

...

1

true

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 callable() {

return new Callable() {

@Override

public String call() throws Exception {

Thread.sleep(2000);

return "Callable result";

}

};

}

@RequestMapping("/view")

public Callable callableWithView(final Model model) {

return new Callable() {

@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 callableWithException(

final @RequestParam(required=false, defaultValue="true") boolean handled) {

http:// return new Callable() {

@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 callableWithCustomTimeoutHandling() {

Callable callable = new Callable() {

@Override

public String call() throws Exception {

Thread.sleep(2000);

return "Callable result";

}

};

return new WebAsyncTask(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")

@ResponseBody

public DeferredResult quotes() {

DeferredResult deferredResult = new DeferredResult();

// 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

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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