Spring Boot @Async 異步任務執行方法

1、任務執行和調度

Spring用TaskExecutor和TaskScheduler接口提供了異步執行和調度任務的抽象。

Spring的TaskExecutor和java.util.concurrent.Executor接口時一樣的，這個接口只有一個方法execute(Runnable task)。

1.1、TaskExecutor類型

Spring已經內置了許多TaskExecutor的實現，你沒有必要自己去實現：

1. SimpleAsyncTaskExecutor 這種實現不會重用任何線程，每次調用都會創建一個新的線程。
2. SyncTaskExecutor 這種實現不會異步的執行
3. ConcurrentTaskExecutor 這種實現是java.util.concurrent.Executor的一個adapter。
4. SimpleThreadPoolTaskExecutor 這種實現實際上是Quartz的SimpleThreadPool的一個子類，它監聽Spring的聲明周期回調。
5. ThreadPoolTaskExecutor 這是最常用最通用的一種實現。它包含了java.util.concurrent.ThreadPoolExecutor的屬性，並且用TaskExecutor進行包裝。

1.2、註解支持調度和異步執行

To enable support for @Scheduled and @Async annotations add @EnableScheduling and @EnableAsync to one of your

 @Configuration classes:@Configuration@EnableAsync@EnableSchedulingpublic class AppConfig {}

特別注意

The default advice mode for processing @Async annotations is "proxy" which allows for interception of calls through the proxy only; local calls within the same class cannot get intercepted that way. For a more advanced mode of interception, consider switching to "aspectj" mode in combination with compile-time or load-time weaving.

默認是用代理去處理@Async的，因此，相同類中的方法調用帶@Async的方法是無法異步的，這種情況仍然是同步。

舉個例子：下面這種，在外部直接調用sayHi()是可以異步執行的，而調用sayHello()時sayHi()仍然是同步執行

public class A { public void sayHello() { sayHi(); } @Async public void sayHi() { } }

1.3、@Async註解

在方法上加@Async註解表示這是一個異步調用。換句話說，方法的調用者會立即得到返回，並且實際的方法執行是想Spring的TaskExecutor提交了一個任務。

In other words, the caller will return immediately upon invocation and the actual execution of the method will occur in a task that has been submitted to a Spring TaskExecutor.

 @Asyncvoid doSomething() { // this will be executed asynchronously}

 @Asyncvoid doSomething(String s) { // this will be executed asynchronously}

 @AsyncFuture<String> returnSomething(int i) { // this will be executed asynchronously}

注意：

@Async methods may not only declare a regular java.util.concurrent.Future return type but also Spring's org.springframework.util.concurrent.ListenableFuture or, as of Spring 4.2, JDK 8's java.util.concurrent.CompletableFuture: for richer interaction with the asynchronous task and for immediate composition with further processing steps.

1.4、@Async限定Executor

默認情況下，當在方法上加@Async註解時，將會使用一個支持註解驅動的Executor。然而，@Async註解的value值可以指定一個別的Executor

 @Async("otherExecutor")void doSomething(String s) { // this will be executed asynchronously by "otherExecutor"}

這裡，otherExecutor是Spring容器中任意Executor bean的名字。

1.5、@Async異常管理

當一個@Async方法有一個Future類型的返回值時，就很容易管理在調Future的get()方法獲取任務的執行結果時拋出的異常。如果返回類型是void，那麼異常是不會被捕獲到的。

 public class MyAsyncUncaughtExceptionHandler implements AsyncUncaughtExceptionHandler { @Override public void handleUncaughtException(Throwable ex, Method method, Object... params) { // handle exception }}

2、線程池配置

import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import org.springframework.scheduling.annotation.EnableAsync;import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;@Configuration@EnableAsyncpublic class TaskExecutorConfig { private Integer corePoolSize = 30; private Integer maxPoolSize = 50; private Integer keepAliveSeconds = 300;// private Integer queueCapacity = 2000; @Bean("myThreadPoolTaskExecutor") public ThreadPoolTaskExecutor myThreadPoolTaskExecutor() { ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor(); executor.setCorePoolSize(corePoolSize); executor.setMaxPoolSize(maxPoolSize); executor.setKeepAliveSeconds(keepAliveSeconds);// executor.setQueueCapacity(queueCapacity); executor.setWaitForTasksToCompleteOnShutdown(true); executor.initialize(); return executor; }}

調用

@Async("myThreadPoolTaskExecutor") @Override public void present(CouponPresentLogEntity entity) { try { CouponBaseResponse rst = couponSendRpcService.send(entity.getUserId(), entity.getCouponBatchKey(), "1", entity.getVendorId()); if (null != rst && rst.isSuccess()) { entity.setStatus(PresentStatusEnum.SUCCESS.getType()); }else { String reason = (null == rst) ? "響應異常" : rst.getMsg(); entity.setFailureReason(reason); entity.setStatus(PresentStatusEnum.FAILURE.getType()); } }catch (Exception ex) { log.error(ex.getMessage(), ex); entity.setFailureReason(ex.getMessage()); entity.setStatus(PresentStatusEnum.FAILURE.getType()); } couponPresentLogDao.update(entity); }

結果

[INFO ] 2018-05-09 16:27:39.887 [myThreadPoolTaskExecutor-1] [com.ourhours.coupon.rpc.dubbo.ReceiveLogFilter] - receive method-name:send; arguments:[10046031,"4d7cc32f8f7e4b00bca56f6bf4b3b658","1",10001]
[INFO ] 2018-05-09 16:27:39.889 [myThreadPoolTaskExecutor-2] [com.ourhours.coupon.rpc.dubbo.ReceiveLogFilter] - receive method-name:send; arguments:[10046031,"4d7cc32f8f7e4b00bca56f6bf4b3b658","1",10001]

參考：

Spring Framework Reference Documentation 4.3.17.RELEASE

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