详细介绍请看Spring DeferredResult 如何实现异步化，从而大大增加长连接数量.

DeferredResult provides an alternative to using a Callable for asynchronous request processing. While aCallable is executed concurrently onbehalf of(代表) the application, with aDeferredResult the application can produce the result from a thread of its choice.

DeferredResult提供了一种使用Callable接口的方式来实现异步请求 . 虽然Callable 是代表应用程序并发执行的，但是使用DeferredResultapplication可以得到结果从它执行的线程中。

Prepare to using the DeferredResult application

// 我目前捕捉不到 他的onError()事件

@Slf4j@CrossOrigin@RestController@SpringBootApplicationpublic class DeferredresultSpringmvcApplication { public static void main(String[] args) { SpringApplication.run(DeferredresultSpringmvcApplication.class, args); } private static ExecutorService executors = Executors.newFixedThreadPool(10); @RequestMapping("/get0") public DeferredResult<HashMap<String, Object>> getData() { log.info("controller 调用的 thread : {}",Thread.currentThread().getName()); log.info("controller 开始执行 "); // 设置超时时间 ,其实只有异步有效 我测试了 ,同步根本不会执行 DeferredResult<HashMap<String, Object>> result = new DeferredResult<>(1000L); result.setResult(getMap()); //如果不是线程执行 , 则返回true executors.execute(new Runnable() { @Override public void run() { // 结果是处理是否成功 有返回结果直接返回 success , 如果 异步请求已过期(必须是异步处理 才会生效) 返回false boolean isok = false; isok = result.setResult(getMap()); log.info("DeferredResult 处理是否成功 : {}", isok); // 成功以后的处理结果 (必须 放到 调用的 Runnable接口里) result.setResultHandler(new DeferredResult.DeferredResultHandler() { @Override public void handleResult(Object result) { log.info("DeferredResult 处理结果 : {} ",result.toString()); } }); } }); // 我这里有问题 // 我调用线程异常全部都是在 超时里面 // 处理异常 , 我捕捉不到这个 异常 ,不知道 哪个地方的 , 其实可以自定义异常 ,然后 根据异常类型进行判断 result.onError((e) -> { log.info("onError"); }); // 完成执行 , 处理结果不管是啥 都会执行 result.onCompletion(new Runnable() { @Override public void run() { log.info("处理 onCompletion"); } }); // 处理超时的处理 , 只有异步结果才会处理 result.onTimeout(new Runnable() { @Override public void run() { log.info("处理超时 onTimeout"); } }); log.info("controller 执行完毕 "); // 记住 只能返回 result , 不能返回null return result; } /** * 不用线程池执行 * @return */ @RequestMapping("/get1") public DeferredResult<HashMap<String, Object>> getByNoExecutor(){ log.info("controller 调用的 thread : {}",Thread.currentThread().getName()); log.info("controller 开始执行 "); DeferredResult<HashMap<String, Object>> result = new DeferredResult<>(3000L); result.setResult(getMap()); log.info("controller 执行完毕 "); return result; } /** * 用线程池执行 * @return */ @RequestMapping("/get2") public DeferredResult<HashMap<String, Object>> getByExecutor(){ log.info("controller 调用的 thread : {}",Thread.currentThread().getName()); log.info("controller 开始执行 "); DeferredResult<HashMap<String, Object>> result = new DeferredResult<>(3000L); executors.execute(new Runnable() { @Override public void run() { result.setResult(getMap()); } }); log.info("controller 执行完毕 "); return result; } /** * 模拟service 服务 * @return */ public HashMap<String, Object> getMap(){ log.info("service 开始执行 "); // 模拟 service 延迟服务 HashMap<String, Object> map = new HashMap<>(); try { Thread.sleep(2000);// int i = 1/0; map.put("key",Thread.currentThread().getName()); log.info("service 服务调用的线程 : {} ",Thread.currentThread().getName()); } catch (Exception e) { throw new RuntimeException(); } log.info("service 执行完毕 "); return map; }}

我们看打印结果 发现

1. get1 执行结果2019-10-12 12:44:17.549 INFO 2020 --- [nio-8080-exec-2] c.s.DeferredresultSpringmvcApplication : controller 调用的 thread : http-nio-8080-exec-22019-10-12 12:44:17.549 INFO 2020 --- [nio-8080-exec-2] c.s.DeferredresultSpringmvcApplication : controller 开始执行 2019-10-12 12:44:17.549 INFO 2020 --- [nio-8080-exec-2] c.s.DeferredresultSpringmvcApplication : service 开始执行 2019-10-12 12:44:19.549 INFO 2020 --- [nio-8080-exec-2] c.s.DeferredresultSpringmvcApplication : service 服务调用的线程 : http-nio-8080-exec-2 2019-10-12 12:44:19.549 INFO 2020 --- [nio-8080-exec-2] c.s.DeferredresultSpringmvcApplication : service 执行完毕 2019-10-12 12:44:19.549 INFO 2020 --- [nio-8080-exec-2] c.s.DeferredresultSpringmvcApplication : controller 执行完毕 2. get2执行结果2019-10-12 12:44:47.993 INFO 2020 --- [nio-8080-exec-4] c.s.DeferredresultSpringmvcApplication : controller 调用的 thread : http-nio-8080-exec-42019-10-12 12:44:47.993 INFO 2020 --- [nio-8080-exec-4] c.s.DeferredresultSpringmvcApplication : controller 开始执行 2019-10-12 12:44:47.994 INFO 2020 --- [nio-8080-exec-4] c.s.DeferredresultSpringmvcApplication : controller 执行完毕 2019-10-12 12:44:47.997 INFO 2020 --- [pool-1-thread-1] c.s.DeferredresultSpringmvcApplication : service 开始执行 2019-10-12 12:44:49.999 INFO 2020 --- [pool-1-thread-1] c.s.DeferredresultSpringmvcApplication : service 服务调用的线程 : pool-1-thread-1 2019-10-12 12:44:49.999 INFO 2020 --- [pool-1-thread-1] c.s.DeferredresultSpringmvcApplication : service 执行完毕

那我们如何自己实现一个呢 ?

/** * 自定义简单使用 * @return */ @RequestMapping("/get3") public MyCallable<HashMap<String, Object>> get(){ log.info("controller 调用的 thread : {}",Thread.currentThread().getName()); log.info("controller 开始执行 "); MyCallable<HashMap<String, Object>> objectMyCallable = new MyCallable<>(); log.info("controller 执行完毕 "); return objectMyCallable; } /** * 简单的执行逻辑 * @param <T> */ private class MyCallable<T> implements Callable<T> { @Override public T call() throws Exception { return (T)getMap(); } } /** * 模拟service 服务 * @return */ public HashMap<String, Object> getMap(){ log.info("service 开始执行 "); // 模拟 service 延迟服务 HashMap<String, Object> map = new HashMap<>(); try { Thread.sleep(2000);// int i = 1/0; map.put("key",Thread.currentThread().getName()); log.info("service 服务调用的线程 : {} ",Thread.currentThread().getName()); } catch (Exception e) { throw new RuntimeException(); } log.info("service 执行完毕 "); return map; }

让我们看一下我们实现的 执行结果

2019-10-12 12:42:23.869 INFO 2020 --- [nio-8080-exec-5] c.s.DeferredresultSpringmvcApplication : controller 调用的 thread : http-nio-8080-exec-52019-10-12 12:42:23.870 INFO 2020 --- [nio-8080-exec-5] c.s.DeferredresultSpringmvcApplication : controller 开始执行 2019-10-12 12:42:23.872 INFO 2020 --- [nio-8080-exec-5] c.s.DeferredresultSpringmvcApplication : controller 执行完毕 2019-10-12 12:42:23.875 INFO 2020 --- [ task-1] c.s.DeferredresultSpringmvcApplication : service 开始执行 2019-10-12 12:42:25.875 INFO 2020 --- [ task-1] c.s.DeferredresultSpringmvcApplication : service 服务调用的线程 : task-1 2019-10-12 12:42:25.875 INFO 2020 --- [ task-1] c.s.DeferredresultSpringmvcApplication : service 执行完毕

这里的task 线程是谁呢 ?

ThreadPoolTaskExecutor 是 springboot自带的默认的 异步线程池 , 我们可以自己设置

@Configurationpublic class AsyncPoolConfig { @Bean public ThreadPoolTaskExecutor asyncThreadPoolTaskExecutor(){ ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor(); executor.setCorePoolSize(20); executor.setMaxPoolSize(200); executor.setQueueCapacity(25); executor.setKeepAliveSeconds(200); executor.setThreadNamePrefix("asyncThread"); executor.setWaitForTasksToCompleteOnShutdown(true); executor.setAwaitTerminationSeconds(60); executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy()); executor.initialize(); return executor; }}

// 复杂的呢

/** * 自定义灵活性 增加代码的可拓展性,加入线程池 * @return */ @RequestMapping("/get4") public MyCallable2<HashMap<String, Object>> get2(){ log.info("controller 调用的 thread : {}",Thread.currentThread().getName()); log.info("controller 开始执行 "); MyCallable2<HashMap<String, Object>> objectMyCallable = new MyCallable2<>(new Callable<HashMap<String, Object>>() { @Override public HashMap<String, Object> call() throws Exception { return getMap(); } }); log.info("controller 执行完毕 "); return objectMyCallable; } /** * 这里 其实 就是 一个 deferred result * @param <T> */ private class MyCallable2<T> implements Callable<T> { private ExecutorService executors = Executors.newFixedThreadPool(10); private Callable<T> callable; public MyCallable2(Callable<T> callable) { this.callable = callable; } // 让一个新的线程执行 call方法 @Override public T call() throws Exception { Future<T> submit = executors.submit(callable); return submit.get(); } } /** * 模拟service 服务 * @return */ public HashMap<String, Object> getMap(){ log.info("service 开始执行 "); // 模拟 service 延迟服务 HashMap<String, Object> map = new HashMap<>(); try { Thread.sleep(2000);// int i = 1/0; map.put("key",Thread.currentThread().getName()); log.info("service 服务调用的线程 : {} ",Thread.currentThread().getName()); } catch (Exception e) { throw new RuntimeException(); } log.info("service 执行完毕 "); return map; }

执行结果

2019-10-12 12:42:44.879 INFO 2020 --- [nio-8080-exec-8] c.s.DeferredresultSpringmvcApplication : controller 调用的 thread : http-nio-8080-exec-82019-10-12 12:42:44.880 INFO 2020 --- [nio-8080-exec-8] c.s.DeferredresultSpringmvcApplication : controller 开始执行 2019-10-12 12:42:44.882 INFO 2020 --- [nio-8080-exec-8] c.s.DeferredresultSpringmvcApplication : controller 执行完毕 2019-10-12 12:42:44.883 INFO 2020 --- [pool-2-thread-1] c.s.DeferredresultSpringmvcApplication : service 开始执行 2019-10-12 12:42:46.884 INFO 2020 --- [pool-2-thread-1] c.s.DeferredresultSpringmvcApplication : service 服务调用的线程 : pool-2-thread-1 2019-10-12 12:42:46.884 INFO 2020 --- [pool-2-thread-1] c.s.DeferredresultSpringmvcApplication : service 执行完毕

​ 感觉我写的很详细 , 其他的就不多说了 , 其实他的应用场景就是 当一个处理请求消耗很长的时间时 , 需要去使用这个 , 主要就是采用发挥一个异步处理的线程事件, 不是返回一个结果 , 这点要明白