引言

在業務處理中，有些業務使用異步的方式更為合理。比如在某個業務邏輯中，把一些數據存入到redis緩存中，緩存只是一個輔助的功能，成功或者失敗對主業務并不會產生根本影響，這個過程可以通過異步的方法去進行。

Spring中通過在方法上設置@Async注解，可使得方法被異步調用。也就是說該方法會在調用時立即返回，而這個方法的實際執行交給Spring的TaskExecutor去完成。

代碼示例

項目是一個普通的Spring的項目，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"> <!-- 包掃描 --> <context:component-scan base-package="com.lzumetal.ssm"/> <!-- 執行異步任務的線程池TaskExecutor --> <task:executor id="myexecutor" pool-size="5" /> <task:annotation-driven executor="myexecutor"/></beans>

兩個Service類：

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;/** * 業務Service */@Servicepublic 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"); } /**  * 獲取異步方法執行的返回值  */ 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()方法是會阻塞的  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;/** * 緩存服務 */@Servicepublic class CacheService { private static final Logger log = LoggerFactory.getLogger(CacheService.class); @Async(value = "myexecutor") //指定執行任務的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");  //返回的結果需要通過AsyncResult這個類包裝  return new AsyncResult<>("Async operation success"); }}

測試類：

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();  //不讓主線程過早結束，否則控制臺看不到異步方法中的輸出內容  TimeUnit.SECONDS.sleep(5L);   } @Test public void testAsyncReturn() throws Exception {  businessService.doBusinessWithAsyncReturn();  TimeUnit.SECONDS.sleep(5L); }}

執行test()方法的結果：

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

執行testAsyncReturn()方法的結果：

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的使用注意點

1. 返回值：不要返回值直接void；需要返回值用AsyncResult或者CompletableFuture
2. 可自定義執行器并指定例如：@Async("otherExecutor")
3. @Async必須不同類間調用： A類—>B類.C方法()（@Async注釋在B類/方法中），如果在同一個類中調用，會變同步執行,例如:A類.B()—>A類.@Async C()。
4. @Async也可以加到類，表示這個類的所有方法都是異步執行，并且方法上的注解會覆蓋類上的注解。但一般不這么用！

以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持VeVb武林網。