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

...

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) {
 
    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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