@Async注解的使用

    在实际开发场景中，不需要等待某个方法执行完成而继续往后执行，那么我们可以将这个方法加上@Async注解放入后台线程（或线程池）中异步执行。简单示例代码如下：

先使用@EnableAsync来开启异步的支持，配置一个线程池：

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@Configuration @EnableAsync public class ThreadPoolConfig {       private static int corePoolSize=30;       private static int maxPoolSize=100;       private static int queueCapacity=100;       private static int keepAliveSeconds=300;       @Bean     public TaskExecutor jobExecutor() {         ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();         // 设置核心线程数         executor.setCorePoolSize(corePoolSize);         // 设置最大线程数         executor.setMaxPoolSize(maxPoolSize);         // 设置队列容量         executor.setQueueCapacity(queueCapacity);         // 设置线程活跃时间（秒）         executor.setKeepAliveSeconds(keepAliveSeconds);         // 设置默认线程名称         executor.setThreadNamePrefix("async-job-thread-");         // 设置拒绝策略rejection-policy：当pool已经达到max size的时候，如何处理新任务 CALLER_RUNS：不在新线程中执行任务，而是有调用者所在的线程来执行         executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());         // 等待所有任务结束后再关闭线程池         executor.setWaitForTasksToCompleteOnShutdown(true);         return executor;     }   }

然后在指定需要异步执行方法上加入@Async注解，并自定线程池（当然可以不指定，直接写@Async）

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@Async("jobExecutor") public void asyncUpdateOrders(){     logger.info(Thread.currentThread().getName()+"异步执行"); }

程序执行入口主程序：

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@RequestMapping(value = "/asyncUpdateOrders") @ResponseBody public String asyncUpdateOrders(HttpServletRequest request) {     try {         logger.info(Thread.currentThread().getName()+"主线程请求异步执行asyncUpdateOrders");         ordersService.asyncUpdateOrders();         logger.info(Thread.currentThread().getName()+"主线程请求异步执行asyncUpdateOrders结束");     } catch (Exception e) {         logger.error(e.getMessage(), e);         return  "false";     }     return "true"; }

　　

执行结果：

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2020-06-23 15:18:59.363 [] [http-nio-8080-exec-1] INFO  o.s.web.servlet.DispatcherServlet :Completed initialization in 10 ms 2020-06-23 15:18:59.396 [] [http-nio-8080-exec-1] INFO  c.y.p.w.c.OrderProcessController :http-nio-8080-exec-1主线程请求异步执行asyncUpdateOrders 2020-06-23 15:18:59.404 [] [http-nio-8080-exec-1] INFO  c.y.p.w.c.OrderProcessController :http-nio-8080-exec-1主线程请求异步执行asyncUpdateOrders结束 2020-06-23 15:18:59.404 [] [async-job-thread-1] INFO  c.y.p.d.s.impl.OrdersServiceImpl :async-job-thread-1异步执行

　　

直接写@Async不指定线程池时，如果线程池配置只配了上面jobExecutor一种，则会默认使用该线程池执行，结果和上面一样，如果线程池配置配置了多个线程池，则此时不指定线程池时则会使用系统默认的SimpleAsyncTaskExecutor线程执行，结果如下：

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2020-06-23 15:23:38.071 [] [http-nio-8080-exec-1] INFO  c.y.p.w.c.OrderProcessController :http-nio-8080-exec-1主线程请求异步执行asyncUpdateOrders 2020-06-23 15:23:38.077 [] [http-nio-8080-exec-1] INFO  o.s.s.a.AnnotationAsyncExecutionInterceptor :More than one TaskExecutor bean found within the context,<br>and none is named 'taskExecutor'. Mark one of them as primary or name it 'taskExecutor' (possibly as an alias) in order to use it for async <br>processing: [jobExecutor, jobBBExecutor] 2020-06-23 15:23:38.079 [] [http-nio-8080-exec-1] INFO  c.y.p.w.c.OrderProcessController :http-nio-8080-exec-1主线程请求异步执行asyncUpdateOrders结束 2020-06-23 15:23:38.079 [] [SimpleAsyncTaskExecutor-1] INFO  c.y.p.d.s.impl.OrdersServiceImpl :SimpleAsyncTaskExecutor-1异步执行