Spring中@Async注解执行异步任务的方法

引言

在业务处理中，有些业务使用异步的方式更为合理。比如在某个业务逻辑中，把一些数据存入到redis缓存中，缓存只是一个辅助的功能，成功或者失败对主业务并不会产生根本影响，这个过程可以通过异步的方法去进行。

Spring中通过在方法上设置@Async注解，可使得方法被异步调用。也就是说该方法会在调用时立即返回，而这个方法的实际执行交给Spring的TaskExecutor去完成。

代码示例

项目是一个普通的Spring的项目，Spring的配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:context="http://www.springframework.org/schema/context"
  xmlns:task="http://www.springframework.org/schema/task"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
  http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
  http://www.springframework.org/schema/context
  http://www.springframework.org/schema/context/spring-context.xsd
  http://www.springframework.org/schema/task
  http://www.springframework.org/schema/task/spring-task.xsd">

 <!-- 包扫描 -->
 <context:component-scan base-package="com.lzumetal.ssm"/>

 <!-- 执行异步任务的线程池TaskExecutor -->
 <task:executor id="myexecutor" pool-size="5" />
 <task:annotation-driven executor="myexecutor"/>

</beans>

两个Service类：

package com.lzumetal.ssm.anotation.service;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;

/**
 * 业务Service
 */
@Service
public class BusinessService {

 private static final Logger log = LoggerFactory.getLogger(BusinessService.class);

 @Autowired
 private CacheService cacheService;

 public void doBusiness() {
  log.error("start to deal with our business");
  cacheService.cacheData();
  log.error("comlete service operation");
 }

 /**
  * 获取异步方法执行的返回值
  */
 public void doBusinessWithAsyncReturn() throws ExecutionException, InterruptedException {
  log.error("start to deal with our business");
  Future<String> future = cacheService.cacheDataWithReturn();
  log.error(future.get()); //future.get()方法是会阻塞的
  log.error("comlete service operation");
 }
}

package com.lzumetal.ssm.anotation.service;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.scheduling.annotation.Async;
import org.springframework.scheduling.annotation.AsyncResult;
import org.springframework.stereotype.Service;

import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

/**
 * 缓存服务
 */
@Service
public class CacheService {

 private static final Logger log = LoggerFactory.getLogger(CacheService.class);

 @Async(value = "myexecutor") //指定执行任务的TaskExecutor
 public void cacheData() {
  try {
   TimeUnit.SECONDS.sleep(3L);
  } catch (InterruptedException e) {
   e.printStackTrace();
  }
  log.error("success store the result to cache");
 }

 @Async
 public Future<String> cacheDataWithReturn() {
  try {
   TimeUnit.SECONDS.sleep(3L);
  } catch (InterruptedException e) {
   e.printStackTrace();
  }
  log.error("success store the result to cache");
  //返回的结果需要通过AsyncResult这个类包装
  return new AsyncResult<>("Async operation success");
 }
}

测试类：

package com.lzumetal.ssm.anotation.test;

import com.lzumetal.ssm.anotation.service.BusinessService;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import java.util.concurrent.TimeUnit;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"classpath:spring-context.xml"})
public class MainTest {

 @Autowired
 private BusinessService businessService;

 @Test
 public void test() throws InterruptedException {
  businessService.doBusiness();
  //不让主线程过早结束，否则控制台看不到异步方法中的输出内容
  TimeUnit.SECONDS.sleep(5L);
 }

 @Test
 public void testAsyncReturn() throws Exception {
  businessService.doBusinessWithAsyncReturn();
  TimeUnit.SECONDS.sleep(5L);
 }

}

执行test()方法的结果：

22:20:33,207  INFO main support.DefaultTestContextBootstrapper:260 - Loaded default TestExecutionListener class names from location [META-INF/spring.factories]: [org.springframework.test.context.web.ServletTestExecutionListener, org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener, org.springframework.test.context.support.DependencyInjectionTestExecutionListener, org.springframework.test.context.support.DirtiesContextTestExecutionListener, org.springframework.test.context.transaction.TransactionalTestExecutionListener, org.springframework.test.context.jdbc.SqlScriptsTestExecutionListener]
22:20:33,226  INFO main support.DefaultTestContextBootstrapper:209 - Could not instantiate TestExecutionListener [org.springframework.test.context.web.ServletTestExecutionListener]. Specify custom listener classes or make the default listener classes (and their required dependencies) available. Offending class: [javax/servlet/ServletContext]
22:20:33,227  INFO main support.DefaultTestContextBootstrapper:187 - Using TestExecutionListeners: [org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener@100fc185, org.springframework.test.context.support.DependencyInjectionTestExecutionListener@643b1d11, org.springframework.test.context.support.DirtiesContextTestExecutionListener@2ef5e5e3, org.springframework.test.context.transaction.TransactionalTestExecutionListener@36d4b5c, org.springframework.test.context.jdbc.SqlScriptsTestExecutionListener@6d00a15d]22:20:33,324  INFO main xml.XmlBeanDefinitionReader:317 - Loading XML bean definitions from class path resource [spring-context.xml]
22:20:33,585  INFO main support.GenericApplicationContext:583 - Refreshing org.springframework.context.support.GenericApplicationContext@4f7d0008: startup date [Wed May 30 22:20:33 CST 2018]; root of context hierarchy
22:20:33,763  INFO main concurrent.ThreadPoolTaskExecutor:165 - Initializing ExecutorService
22:20:33,766  INFO main support.PostProcessorRegistrationDelegate$BeanPostProcessorChecker:325 - Bean 'myexecutor' of type [org.springframework.scheduling.config.TaskExecutorFactoryBean] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
22:20:33,767  INFO main support.PostProcessorRegistrationDelegate$BeanPostProcessorChecker:325 - Bean 'myexecutor' of type [org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
22:20:34,107 ERROR main service.BusinessService:24 - start to deal with our business
22:20:34,113 ERROR main service.BusinessService:26 - comlete service operation
22:20:37,166 ERROR myexecutor-1 service.CacheService:28 - success store the result to cache
22:20:39,117  INFO Thread-0 support.GenericApplicationContext:984 - Closing org.springframework.context.support.GenericApplicationContext@4f7d0008: startup date [Wed May 30 22:20:33 CST 2018]; root of context hierarchy
22:20:39,118  INFO Thread-0 concurrent.ThreadPoolTaskExecutor:203 - Shutting down ExecutorService

执行testAsyncReturn()方法的结果：

21:38:16,908  INFO main support.DefaultTestContextBootstrapper:260 - Loaded default TestExecutionListener class names from location [META-INF/spring.factories]: [org.springframework.test.context.web.ServletTestExecutionListener, org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener, org.springframework.test.context.support.DependencyInjectionTestExecutionListener, org.springframework.test.context.support.DirtiesContextTestExecutionListener, org.springframework.test.context.transaction.TransactionalTestExecutionListener, org.springframework.test.context.jdbc.SqlScriptsTestExecutionListener]
21:38:16,926  INFO main support.DefaultTestContextBootstrapper:209 - Could not instantiate TestExecutionListener [org.springframework.test.context.web.ServletTestExecutionListener]. Specify custom listener classes or make the default listener classes (and their required dependencies) available. Offending class: [javax/servlet/ServletContext]
21:38:16,927  INFO main support.DefaultTestContextBootstrapper:187 - Using TestExecutionListeners: [org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener@100fc185, org.springframework.test.context.support.DependencyInjectionTestExecutionListener@643b1d11, org.springframework.test.context.support.DirtiesContextTestExecutionListener@2ef5e5e3, org.springframework.test.context.transaction.TransactionalTestExecutionListener@36d4b5c, org.springframework.test.context.jdbc.SqlScriptsTestExecutionListener@6d00a15d]21:38:17,025  INFO main xml.XmlBeanDefinitionReader:317 - Loading XML bean definitions from class path resource [spring-context.xml]
21:38:17,263  INFO main support.GenericApplicationContext:583 - Refreshing org.springframework.context.support.GenericApplicationContext@4f7d0008: startup date [Wed May 30 21:38:17 CST 2018]; root of context hierarchy
21:38:17,405  INFO main concurrent.ThreadPoolTaskExecutor:165 - Initializing ExecutorService
21:38:17,407  INFO main support.PostProcessorRegistrationDelegate$BeanPostProcessorChecker:325 - Bean 'myexecutor' of type [org.springframework.scheduling.config.TaskExecutorFactoryBean] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
21:38:17,407  INFO main support.PostProcessorRegistrationDelegate$BeanPostProcessorChecker:325 - Bean 'myexecutor' of type [org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
21:38:17,692 ERROR main service.BusinessService:35 - start to deal with our business
21:38:20,833 ERROR myexecutor-1 service.CacheService:39 - success store the result to cache
21:38:20,834 ERROR main service.BusinessService:37 - Async operation success
21:38:20,835 ERROR main service.BusinessService:38 - comlete service operation
21:38:25,838  INFO Thread-0 support.GenericApplicationContext:984 - Closing org.springframework.context.support.GenericApplicationContext@4f7d0008: startup date [Wed May 30 21:38:17 CST 2018]; root of context hierarchy
21:38:25,839  INFO Thread-0 concurrent.ThreadPoolTaskExecutor:203 - Shutting down ExecutorService

@Async的使用注意点

1. 返回值：不要返回值直接void；需要返回值用AsyncResult或者CompletableFuture
2. 可自定义执行器并指定例如：@Async("otherExecutor")
3. @Async必须不同类间调用： A类—>B类.C方法()（@Async注释在B类/方法中），如果在同一个类中调用，会变同步执行,例如:A类.B()—>A类.@Async C()。
4. @Async也可以加到类，表示这个类的所有方法都是异步执行，并且方法上的注解会覆盖类上的注解。但一般不这么用！

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