Spring Boot @Async 异步任务执行方法

1、任务执行和调度

Spring用TaskExecutor和TaskScheduler接口提供了异步执行和调度任务的抽象。

Spring的TaskExecutor和java.util.concurrent.Executor接口时一样的，这个接口只有一个方法execute(Runnable task)。

1.1、TaskExecutor类型

Spring已经内置了许多TaskExecutor的实现，你没有必要自己去实现：

1. SimpleAsyncTaskExecutor  这种实现不会重用任何线程，每次调用都会创建一个新的线程。
2. SyncTaskExecutor  这种实现不会异步的执行
3. ConcurrentTaskExecutor  这种实现是java.util.concurrent.Executor的一个adapter。
4. SimpleThreadPoolTaskExecutor  这种实现实际上是Quartz的SimpleThreadPool的一个子类，它监听Spring的声明周期回调。
5. ThreadPoolTaskExecutor  这是最常用最通用的一种实现。它包含了java.util.concurrent.ThreadPoolExecutor的属性，并且用TaskExecutor进行包装。

1.2、注解支持调度和异步执行

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

@Configuration classes:

@Configuration
@EnableAsync
@EnableScheduling
public class AppConfig {
}

特别注意

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.

默认是用代理去处理@Async的，因此，相同类中的方法调用带@Async的方法是无法异步的，这种情况仍然是同步。

举个例子：下面这种，在外部直接调用sayHi()是可以异步执行的，而调用sayHello()时sayHi()仍然是同步执行

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

  @Async
  public void sayHi() {

  }   
}

1.3、@Async注解

在方法上加@Async注解表示这是一个异步调用。换句话说，方法的调用者会立即得到返回，并且实际的方法执行是想Spring的TaskExecutor提交了一个任务。

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.

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

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

@Async
Future<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

默认情况下，当在方法上加@Async注解时，将会使用一个支持注解驱动的Executor。然而，@Async注解的value值可以指定一个别的Executor

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

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

1.5、@Async异常管理

当一个@Async方法有一个Future类型的返回值时，就很容易管理在调Future的get()方法获取任务的执行结果时抛出的异常。如果返回类型是void，那么异常是不会被捕获到的。

public class MyAsyncUncaughtExceptionHandler implements AsyncUncaughtExceptionHandler {

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

2、线程池配置

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
@EnableAsync
public 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;
  }
}

调用

@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) ? "响应异常" : 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);
  }

结果

[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]

参考：

Spring Framework Reference Documentation 4.3.17.RELEASE

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