Spring Boot 异步执行方法

最近遇到一个需求，就是当服务器接到请求并不须要任务执行完成才返回结果，能够当即返回结果，让任务异步的去执行。开始考虑是直接启一个新的线程去执行任务或者把任务提交到一个线程池去执行，这两种方法都是能够的。可是 Spring 这么强大，确定有什么更简单的方法，就 google 了一下，还真有呢。就是使用 @EnableAsync 和 @Async 这两个注解就 ok 了。

给方法加上 @Async 注解

package me.deweixu.aysncdemo.service;

public interface AsyncService {

    void asyncMethod(String arg);
}

package me.deweixu.aysncdemo.service.ipml;

import me.deweixu.aysncdemo.service.AsyncService;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Service;

@Service
public class AsyncServiceImpl implements AsyncService {

    @Async
    @Override
    public void asyncMethod(String arg) {
        System.out.println("arg:" + arg);
        System.out.println("=====" + Thread.currentThread().getName() + "=========");
    }
}

@EnableAsync

在启动类或者配置类加上 @EnableAsync 注解

package me.deweixu.aysncdemo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableAsync;

@EnableAsync
@SpringBootApplication
public class AysncDemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(AysncDemoApplication.class, args);
    }
}

测试

package me.deweixu.aysncdemo;

import me.deweixu.aysncdemo.service.AsyncService;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class AysncDemoApplicationTests {

    @Autowired
    AsyncService asyncService;

    @Test
    public void testAsync() {
        System.out.println("=====" + Thread.currentThread().getName() + "=========");
        asyncService.asyncMethod("Async");
    }

}

=====main=========
2018-03-25 21:30:31.391  INFO 28742 --- [           main] .s.a.AnnotationAsyncExecutionInterceptor : No task executor bean found for async processing: no bean of type TaskExecutor and no bean named 'taskExecutor' either
arg:Async
=====SimpleAsyncTaskExecutor-1=========

从上面的结果看 asyncService.asyncMethod("Async") 确实异步执行了，它使用了一个新的线程。

指定 Executor

从上面执行的日志能够猜想到 Spring 默认使用 SimpleAsyncTaskExecutor 来异步执行任务的，能够搜索到这个类。@Async 也能够指定自定义的 Executor。

在启动类中增长自定义的 Executor

package me.deweixu.aysncdemo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;

import java.util.concurrent.Executor;

@EnableAsync
@SpringBootApplication
public class AysncDemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(AysncDemoApplication.class, args);
    }

    @Bean(name = "threadPoolTaskExecutor")
    public Executor threadPoolTaskExecutor() {
        return new ThreadPoolTaskExecutor();
    }
}

指定 Executor

package me.deweixu.aysncdemo.service.ipml;

import me.deweixu.aysncdemo.service.AsyncService;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Service;

@Service
public class AsyncServiceImpl implements AsyncService {

    @Async("threadPoolTaskExecutor")
    @Override
    public void asyncMethod(String arg) {
        System.out.println("arg:" + arg);
        System.out.println("=====" + Thread.currentThread().getName() + "=========");
    }
}

这样在异步执行任务的时候就使用 threadPoolTaskExecutor

设置默认的 Executor

上面提到若是 @Async 不指定 Executor 就默认使用 SimpleAsyncTaskExecutor，其实默认的 Executor 是能够使用 AsyncConfigurer 接口来配置的

@Configuration
public class SpringAsyncConfig implements AsyncConfigurer {
     
    @Override
    public Executor getAsyncExecutor() {
        return new ThreadPoolTaskExecutor();
    }
     
}

异常捕获

在异步执行的方法中是可能出现异常的，咱们能够在任务内部使用 try catch 来处理异常，当任务抛出异常时，Spring 也提供了捕获它的方法。

实现 AsyncUncaughtExceptionHandler 接口

public class CustomAsyncExceptionHandler
  implements AsyncUncaughtExceptionHandler {
 
    @Override
    public void handleUncaughtException(
      Throwable throwable, Method method, Object... obj) {
  
        System.out.println("Exception message - " + throwable.getMessage());
        System.out.println("Method name - " + method.getName());
        for (Object param : obj) {
            System.out.println("Parameter value - " + param);
        }
    }
     
}

实现 AsyncConfigurer 接口重写 getAsyncUncaughtExceptionHandler 方法

@Configuration
public class SpringAsyncConfig implements AsyncConfigurer {
     
    @Override
    public Executor getAsyncExecutor() {
        return new ThreadPoolTaskExecutor();
    }
    
    @Override
    public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
        return new CustomAsyncExceptionHandler();
    }

     
}

改写 asyncMethod 方法使它抛出异常

@Async
    @Override
    public void asyncMethod(String arg) {
        System.out.println("arg:" + arg);
        System.out.println("=====" + Thread.currentThread().getName() + "=========");
        throw new NullPointerException();
    }

运行结果：

=====main=========
arg:Async
=====threadPoolTaskExecutor-1=========
Exception message - Async NullPointerException
Method name - asyncMethod
Parameter value - Async

正确捕获到了异常。