springmvc的异步特性介绍

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1.为什么需要异步模式

异步其实是个老生常谈的话题，异步的本质在于请求处理线程不在阻塞，工作线程完成处理后勾起一个回调处理线程（回调处理线程和请求处理线程原因），由回调处理线程向浏览器反馈结果。

2.springMvc在4.x版本开始支持异步

环境要求，Servlet版本是3.x以上，Spring MVC版本是4.x以上，建议使用最新，例如:

    
      javax.servlet
      javax.servlet-api
      3.1.0
      provided
    
    
      org.springframework
      spring-webmvc
      4.2.3.RELEASE
    

3.使用DefferedResult特性

由于Spring MVC的良好封装，异步功能使用特别简单。在Controller中，传统的同步模式返回的ModelAndView，而异步模式则是返回DeferredResult

    @GetMapping("/sync")
    public DeferredResult sync() {
        DeferredResult result = new DeferredResult();
        LOGGER.info("start....");
        longTimeAsyncCallService.exec((ret) -> {
            LOGGER.info("sync complete...." + ret);
            result.setResult("OK");
        });
        return result;
    }

结果：
[nio-8080-exec-1] com.example.demo.DemoController          : start....
[nio-8080-exec-1] c.example.demo.LongTimeAsyncCallService  : 完成此任务需要等待:5秒.
[pool-1-thread-1] c.example.demo.LongTimeAsyncCallService  : sync start.
[pool-1-thread-1] com.example.demo.DemoController          : sync complete....callback result 3

4.使用WebAsyncTask特性

与上一个不同之处在于返回WebAsyncTask的话是不需要我们主动去调用Callback的，它仅仅是简单地把请求处理线程的任务转交给另一工作线程而已

   @GetMapping("/sync2")
    public WebAsyncTask syncTask() {
        LOGGER.info("start....");
        Callable callable = new Callable() {
            public String call() throws Exception {
                Thread.sleep(5000); //假设是一些长时间任务
                LOGGER.info("exec sync complete....");
                return "suc";
            }
        };
        return new WebAsyncTask(callable);
    }

结果：
[nio-8080-exec-4] com.example.demo.DemoController          : start....
[      my-task-2] com.example.demo.DemoController          : exec sync complete....

5.超时处理

    @GetMapping("/sync-timeout")
    public DeferredResult syncTimeout() {
        DeferredResult deferredResult = new DeferredResult(2000L);
        LOGGER.info("start....timeout:2s");
        longTimeAsyncCallService.exec(new LongTermTaskCallback() {
            @Override
            public void callback(Object result) {
                LOGGER.info("exec sync complete...." + result);
                deferredResult.setResult("Ok");
            }
        });
        deferredResult.onTimeout(new Runnable() {
            @Override
            public void run() {
                LOGGER.info("exec timeout complete....");
                deferredResult.setResult("timeout");
            }
        });
        return deferredResult;
    }

DefferedResult结果：
    [nio-8080-exec-7] com.example.demo.DemoController          : start....timeout:2s
    [nio-8080-exec-7] c.example.demo.LongTimeAsyncCallService  : 完成此任务需要等待:5秒.
    [nio-8080-exec-8] com.example.demo.DemoController          : exec timeout complete....
    [pool-1-thread-1] c.example.demo.LongTimeAsyncCallService  : sync start.
    [pool-1-thread-1] com.example.demo.DemoController          : exec sync complete....callback result 8

    @GetMapping("/sync-timeout2")
    public WebAsyncTask syncTaskTimeout() {
        LOGGER.info("start....timeout:2s");
        Callable callable = new Callable() {
            public String call() throws Exception {
                Thread.sleep(5000); //假设是一些长时间任务
                LOGGER.info("exec sync complete....");
                return "suc";
            }
        };
        WebAsyncTask asyncTask = new WebAsyncTask(2000, callable);
        asyncTask.onTimeout(new Callable() {
            public String call() throws Exception {
                LOGGER.info("exec timeout complete....");
                return "timeout";
            }
        });
        return asyncTask;
    }

 WebAsyncTask结果：
    [io-8080-exec-10] com.example.demo.DemoController          : start....timeout:2s
    [nio-8080-exec-1] com.example.demo.DemoController          : exec timeout complete....
    [      my-task-3] com.example.demo.DemoController          : exec sync complete....

源码：https://github.com/alex2chen/springboot-sync-web