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詳解spring mvc對(duì)異步請(qǐng)求的處理

更新時(shí)間：2017年01月03日 10:41:27 作者：自行車(chē)上的程序員

spring mvc3.2及以上版本增加了對(duì)請(qǐng)求的異步處理，是在servlet3的基礎(chǔ)上進(jìn)行封裝的，有興趣的可以了解一下。

在spring mvc3.2及以上版本增加了對(duì)請(qǐng)求的異步處理，是在servlet3的基礎(chǔ)上進(jìn)行封裝的。

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、聲明version="3.0"，聲明web-app_3_0.xsd

1.2、為servlet或者filter設(shè)置啟用異步支持： <async-supported>true</async-supported> ，修改WEB應(yīng)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類(lèi)支持async

2.1、返回java.util.concurrent.Callable來(lái)完成異步處理

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、在異步處理完成時(shí)返回org.springframework.web.context.request.async.DeferredResult其他線程，例如一個(gè)JMS或一個(gè)AMQP消息,Redis通知等等：

@RequestMapping("/quotes")
@ResponseBody
public 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的聲明必須大于等于3.2

<mvc:annotation-driven>
<!-- 可不設(shè)置，使用默認(rèn)的超時(shí)時(shí)間 -->
  <mvc:async-support default-timeout="3000"/>
</mvc:annotation-driven>

實(shí)際使用示例：

function deferred(){
  $.get('quotes.htm',function(data){
    console.log(data);
    deferred();//每次請(qǐng)求完成,再發(fā)一次請(qǐng)求,避免客戶(hù)端定時(shí)刷新來(lái)獲取數(shù)據(jù)
  });
}

這么做的好處避免web server的連接池被長(zhǎng)期占用而引起性能問(wèn)題，調(diào)用后生成一個(gè)非web的服務(wù)線程來(lái)處理，增加web服務(wù)器的吞吐量~~

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