Spring Boot 入门 - 进阶篇（2）- 异步调用(@Async)

异步处理

• Java的异步处理Thread/Runnable、Callable/Future
• Servlet 2.5的异步处理 Tomcat的CometProcessor、Jetty的Continuations
• Servlet 3.0的异步处理 asyncSupported、AsyncContext
• Spring MVC的异步处理 @Async、AsyncTaskExecutor
• Spring MVC的SSE ResponseBodyEmitter、SseEmitter、StreamingResponseBody

Spring Boot本身对异步调用没有多大的变动，基本还是Spring MVC的@Async。

（1）开启Spring的异步支持

@Configuration
@EnableAsync
public class SpringAsyncConfig { 

}

开启@EnableWebMvc的时候也自动开启了异步处理，但在Spring Boot项目中是不能使用@EnableWebMvc的。它会使Spring Boot的AutoConfigure一部分功能失效。
官方文档里有说明：
http://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#boot-features-spring-mvc-auto-configuration

@EnableWebMvc
@ComponentScan("com.example.component")
@Configuration
public class WebMvcConfig extends WebMvcConfigurerAdapter {

    @Override
    public void configureAsyncSupport(AsyncSupportConfigurer configurer) {
        configurer.setTaskExecutor(mvcAsyncExecutor());
    }

    @Bean
    public AsyncTaskExecutor mvcAsyncExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setMaxPoolSize(10);
        return executor;
    }
}

（2）定义需要执行异步处理的方法

1）没有返回值

@Async
public void asyncMethodWithVoidReturnType() {
    System.out.println("Execute method asynchronously. "
      + Thread.currentThread().getName());
}

2）带返回值

@Async
public Future<String> asyncMethodWithReturnType() {
    System.out.println("Execute method asynchronously - "
      + Thread.currentThread().getName());
    try {
        Thread.sleep(5000);
        return new AsyncResult<String>("hello world !");
    } catch (InterruptedException e) {
    }
 
    return null;
}

（3）异步线程池的定义

1）一个线程池

@Configuration
@EnableAsync
public class SpringAsyncConfig {
    @Bean
    public AsyncTaskExecutor taskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setMaxPoolSize(10);
        return executor;
    }
}

2）多个线程池

@Configuration
@EnableAsync
public class SpringAsyncConfig {
     
    @Bean(name = "threadPoolTaskExecutor1")
    public Executor threadPoolTaskExecutor() {
        return new ThreadPoolTaskExecutor();
    }
     
    @Bean(name = "threadPoolTaskExecutor2")
    public Executor threadPoolTaskExecutor() {
        return new ThreadPoolTaskExecutor();
    }

}

@Async("threadPoolTaskExecutor1")
public void asyncMethodWithConfiguredExecutor() {
    System.out.println("Execute method with configured executor - "
      + Thread.currentThread().getName());
}

（4）异步异常的处理

public interface AsyncConfigurer {
    Executor getAsyncExecutor();
    AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler();
}

AsyncConfigurerSupport是AsyncConfigurer接口的实现但里边什么也没做。

@Configuration
@EnableAsync
class SpringAsyncConfigurer extends AsyncConfigurerSupport {

    @Bean
    public ThreadPoolTaskExecutor asyncExecutor() {
        ThreadPoolTaskExecutor threadPool = new ThreadPoolTaskExecutor();
        threadPool.setCorePoolSize(3);
        threadPool.setMaxPoolSize(3);
        threadPool.setWaitForTasksToCompleteOnShutdown(true);
        threadPool.setAwaitTerminationSeconds(60 * 15);
        return threadPool;
    }

    @Override
    public Executor getAsyncExecutor() {
        return asyncExecutor;
    }
}

可以自己实现AsyncConfigurer接口处理异常。

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

    @Override
    public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
        return new CustomAsyncExceptionHandler();
    }

}

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);
        }
    }
     
}

参考：
http://qiita.com/kazuki43zoo/items/8be79f98621f90865b78
http://qiita.com/kazuki43zoo/items/ce88dea403c596249e8a
http://qiita.com/kazuki43zoo/items/53b79fe91c41cc5c2e59