spring mvc对异步请求的处理

冷不防 2021-09-25 22:02 387阅读 0赞

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

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<?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>

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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

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<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>

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2、使controller类支持async

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

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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();
        }
      
    }

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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：

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@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

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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>
    
        <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~~

可以看下这个blog，还不错：http://wiselyman.iteye.com/blog/2215852

[copycode.gif]: /images/20210923/6666b868d26d4310b74efb1a10a678ba.png