一、Spring中实现异步执行
在这里我先以事件的机制举例，注意默认情况下事件的发布与监听都是同步执行的。那么我们来看一看基于异步事件的例子该怎么写
首先还是定义事件：
package com.bdqn.lyrk.ssm.study.app.entity.event;
import org.springframework.context.ApplicationEvent;
/**
* 定义一个饥饿的事件
*
* @author chen.nie
* @date 2018/6/26
**/
public class HungryEvent extends ApplicationEvent {
/**
* Create a new ApplicationEvent.
*
* @param source the object on which the event initially occurred (never {@code null})
*/
public HungryEvent(Object source) {
super(source);
}
}
定义一个Person类，该类主要发布相关事件
package com.bdqn.lyrk.ssm.study.app.entity.event;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationEventPublisherAware;
import org.springframework.stereotype.Component;
import static com.bdqn.lyrk.ssm.study.app.utils.Printer.print;
@Component
public class Person implements ApplicationEventPublisherAware {
private int hungry;
private String name = "admin";
public String getName() {
return name;
}
private ApplicationEventPublisher applicationEventPublisher;
public void setHungry(int hungry) {
this.hungry = hungry;
}
public void work(){
if (hungry < 10) {
print("饿了，谁来帮我做做饭..");
applicationEventPublisher.publishEvent(new HungryEvent(this));
}
print("继续工作....");
}
@Override
public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
this.applicationEventPublisher = applicationEventPublisher;
}
}
定义事件的监听者
package com.bdqn.lyrk.ssm.study.app.entity;
import com.bdqn.lyrk.ssm.study.app.entity.event.HungryEvent;
import com.bdqn.lyrk.ssm.study.app.entity.event.Person;
import org.springframework.context.event.EventListener;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Component;
import static com.bdqn.lyrk.ssm.study.app.utils.Printer.print;
@Component
public class TeacherEntity {
@Async
@EventListener(HungryEvent.class)
public void cook(HungryEvent hungryEvent) throws InterruptedException {
Person person = (Person) hungryEvent.getSource();
print(person.getName() + "饿了开始做饭");
Thread.sleep(5000);
print("饭做好了...");
}
}
在这里@Async表明调用该方法时，会开启一个线程进行异步执行。@EventListener表明该方法会监听对应的事件
AppConfig的配置
@Configuration
@ComponentScan
@EnableAsync
public class AppConfig{
/**
* 定义异步线程任务
*
* @author chen.nie
* @date 2018/6/27
**/
@Bean
public Executor taskExecutor() {
ExecutorService executorService = Executors.newSingleThreadExecutor();
return executorService;
}
}
在这里顺便用Printer方法打印出线程名称
public class Printer {
public static void print(String content) {
System.out.printf("[%s]--%s%n", Thread.currentThread().getName(), content);
}
}
main方法：
public static void main(String[] args) {
AnnotationConfigApplicationContext appApplicationContext = new AnnotationConfigApplicationContext(AppConfig.class);
Person person = appApplicationContext.getBean(Person.class);
person.setHungry(1);
person.work();
appApplicationContext.close();
}
执行结果：
[main]--饿了，谁来帮我做做饭.. [main]--继续工作.... [pool-1-thread-1]--admin饿了开始做饭 [pool-1-thread-1]--饭做好了...
二、Async的原理分析
2.1 @EnableAsync
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AsyncConfigurationSelector.class)
public @interface EnableAsync {
/**
* Indicate the 'async' annotation type to be detected at either class
* or method level.
* <p>By default, both Spring's @{@link Async} annotation and the EJB 3.1
* {@code @javax.ejb.Asynchronous} annotation will be detected.
* <p>This attribute exists so that developers can provide their own
* custom annotation type to indicate that a method (or all methods of
* a given class) should be invoked asynchronously.
*/
Class<? extends Annotation> annotation() default Annotation.class;
/**
* Indicate whether subclass-based (CGLIB) proxies are to be created as opposed
* to standard Java interface-based proxies.
* <p><strong>Applicable only if the {@link #mode} is set to {@link AdviceMode#PROXY}</strong>.
* <p>The default is {@code false}.
* <p>Note that setting this attribute to {@code true} will affect <em>all</em>
* Spring-managed beans requiring proxying, not just those marked with {@code @Async}.
* For example, other beans marked with Spring's {@code @Transactional} annotation
* will be upgraded to subclass proxying at the same time. This approach has no
* negative impact in practice unless one is explicitly expecting one type of proxy
* vs. another — for example, in tests.
*/
boolean proxyTargetClass() default false;
/**
* Indicate how async advice should be applied.
* <p>The default is {@link AdviceMode#PROXY}.
* @see AdviceMode
*/
AdviceMode mode() default AdviceMode.PROXY;
/**
* Indicate the order in which the {@link AsyncAnnotationBeanPostProcessor}
* should be applied.
* <p>The default is {@link Ordered#LOWEST_PRECEDENCE} in order to run
* after all other post-processors, so that it can add an advisor to
* existing proxies rather than double-proxy.
*/
int order() default Ordered.LOWEST_PRECEDENCE;
}
绝大多数的特性注解@EnableXXX都有个特性使用@Import进行导入操作，那么我们不妨在看一下AsyncConfigurationSelector这个类
public class AsyncConfigurationSelector extends AdviceModeImportSelector<EnableAsync> {
private static final String ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME =
"org.springframework.scheduling.aspectj.AspectJAsyncConfiguration";
/**
* {@inheritDoc}
* @return {@link ProxyAsyncConfiguration} or {@code AspectJAsyncConfiguration} for
* {@code PROXY} and {@code ASPECTJ} values of {@link EnableAsync#mode()}, respectively
*/
@Override
public String[] selectImports(AdviceMode adviceMode) {
switch (adviceMode) {
case PROXY:
return new String[] { ProxyAsyncConfiguration.class.getName() };
case ASPECTJ:
return new String[] { ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME };
default:
return null;
}
}
}
看到这里我们已经能猜到Spring中的Async是基于AOP实现的，毕竟我们看到了AspectJ与Proxy了嘛
2.2、ProxyAsyncConfiguration
/*
* Copyright 2002-2015 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.scheduling.annotation;
import java.lang.annotation.Annotation;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Role;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.scheduling.config.TaskManagementConfigUtils;
import org.springframework.util.Assert;
/**
* {@code @Configuration} class that registers the Spring infrastructure beans necessary
* to enable proxy-based asynchronous method execution.
*
* @author Chris Beams
* @author Stephane Nicoll
* @since 3.1
* @see EnableAsync
* @see AsyncConfigurationSelector
*/
@Configuration
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public class ProxyAsyncConfiguration extends AbstractAsyncConfiguration {
@Bean(name = TaskManagementConfigUtils.ASYNC_ANNOTATION_PROCESSOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public AsyncAnnotationBeanPostProcessor asyncAdvisor() {
Assert.notNull(this.enableAsync, "@EnableAsync annotation metadata was not injected");
AsyncAnnotationBeanPostProcessor bpp = new AsyncAnnotationBeanPostProcessor();
Class<? extends Annotation> customAsyncAnnotation = this.enableAsync.getClass("annotation");
if (customAsyncAnnotation != AnnotationUtils.getDefaultValue(EnableAsync.class, "annotation")) {
bpp.setAsyncAnnotationType(customAsyncAnnotation);
}
if (this.executor != null) {
bpp.setExecutor(this.executor);
}
if (this.exceptionHandler != null) {
bpp.setExceptionHandler(this.exceptionHandler);
}
bpp.setProxyTargetClass(this.enableAsync.getBoolean("proxyTargetClass"));
bpp.setOrder(this.enableAsync.<Integer>getNumber("order"));
return bpp;
}
}
在这里我们可以看到此类是一个Spring的配置类，主要用于创建AsyncAnnotationBeanPostProcessor的Bean
2.3、AsyncAnnotationBeanPostProcessor
首先我先贴一下这个类图：
我们先看一下它的父类AbstractAdvisingBeanPostProcessor里重写的方法，在该方法里动态改变Bean的相关属性
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) {
if (bean instanceof AopInfrastructureBean) {
// Ignore AOP infrastructure such as scoped proxies.
return bean;
}
// 如果为Advised对象且当前的bean适配当前的Advice，则将advisor添加到Advised里
if (bean instanceof Advised) {
Advised advised = (Advised) bean;
if (!advised.isFrozen() && isEligible(AopUtils.getTargetClass(bean))) {
// Add our local Advisor to the existing proxy's Advisor chain...
if (this.beforeExistingAdvisors) {
advised.addAdvisor(0, this.advisor);
}
else {
advised.addAdvisor(this.advisor);
}
return bean;
}
}
// 如果当前的bean复合当前的通知
if (isEligible(bean, beanName)) {
ProxyFactory proxyFactory = prepareProxyFactory(bean, beanName);
if (!proxyFactory.isProxyTargetClass()) {
evaluateProxyInterfaces(bean.getClass(), proxyFactory);
}
proxyFactory.addAdvisor(this.advisor);
customizeProxyFactory(proxyFactory);
return proxyFactory.getProxy(getProxyClassLoader());
}
// No async proxy needed.
return bean;
}
而AsyncAnnotationBeanPostProcessor 重写了BeanFactoryAware接口方法，请大家关注一下属性Executor和setBeanFactory方法：
public class AsyncAnnotationBeanPostProcessor extends AbstractBeanFactoryAwareAdvisingPostProcessor {
/**
* The default name of the {@link TaskExecutor} bean to pick up: "taskExecutor".
* <p>Note that the initial lookup happens by type; this is just the fallback
* in case of multiple executor beans found in the context.
* @since 4.2
* @see AnnotationAsyncExecutionInterceptor#DEFAULT_TASK_EXECUTOR_BEAN_NAME
*/
public static final String DEFAULT_TASK_EXECUTOR_BEAN_NAME =
AnnotationAsyncExecutionInterceptor.DEFAULT_TASK_EXECUTOR_BEAN_NAME;
protected final Log logger = LogFactory.getLog(getClass());
private Class<? extends Annotation> asyncAnnotationType;
private Executor executor;
private AsyncUncaughtExceptionHandler exceptionHandler;
public AsyncAnnotationBeanPostProcessor() {
setBeforeExistingAdvisors(true);
}
/**
* Set the 'async' annotation type to be detected at either class or method
* level. By default, both the {@link Async} annotation and the EJB 3.1
* {@code javax.ejb.Asynchronous} annotation will be detected.
* <p>This setter property exists so that developers can provide their own
* (non-Spring-specific) annotation type to indicate that a method (or all
* methods of a given class) should be invoked asynchronously.
* @param asyncAnnotationType the desired annotation type
*/
public void setAsyncAnnotationType(Class<? extends Annotation> asyncAnnotationType) {
Assert.notNull(asyncAnnotationType, "'asyncAnnotationType' must not be null");
this.asyncAnnotationType = asyncAnnotationType;
}
/**
* Set the {@link Executor} to use when invoking methods asynchronously.
* <p>If not specified, default executor resolution will apply: searching for a
* unique {@link TaskExecutor} bean in the context, or for an {@link Executor}
* bean named "taskExecutor" otherwise. If neither of the two is resolvable,
* a local default executor will be created within the interceptor.
* @see AsyncAnnotationAdvisor#AsyncAnnotationAdvisor(Executor, AsyncUncaughtExceptionHandler)
* @see AnnotationAsyncExecutionInterceptor#getDefaultExecutor(BeanFactory)
* @see #DEFAULT_TASK_EXECUTOR_BEAN_NAME
*/
public void setExecutor(Executor executor) {
this.executor = executor;
}
/**
* Set the {@link AsyncUncaughtExceptionHandler} to use to handle uncaught
* exceptions thrown by asynchronous method executions.
* @since 4.1
*/
public void setExceptionHandler(AsyncUncaughtExceptionHandler exceptionHandler) {
this.exceptionHandler = exceptionHandler;
}
@Override
public void setBeanFactory(BeanFactory beanFactory) {
super.setBeanFactory(beanFactory);
AsyncAnnotationAdvisor advisor = new AsyncAnnotationAdvisor(this.executor, this.exceptionHandler);
if (this.asyncAnnotationType != null) {
advisor.setAsyncAnnotationType(this.asyncAnnotationType);
}
advisor.setBeanFactory(beanFactory);
this.advisor = advisor;
}
}
在这里指定对应的this.advisor为AsyncAnnotationAdvisor。
2.4、AsyncAnnotationAdvisor
在这里我们先看看它的构造函数：
public AsyncAnnotationAdvisor(Executor executor, AsyncUncaughtExceptionHandler exceptionHandler) {
Set<Class<? extends Annotation>> asyncAnnotationTypes = new LinkedHashSet<Class<? extends Annotation>>(2);
asyncAnnotationTypes.add(Async.class);
try {
asyncAnnotationTypes.add((Class<? extends Annotation>)
ClassUtils.forName("javax.ejb.Asynchronous", AsyncAnnotationAdvisor.class.getClassLoader()));
}
catch (ClassNotFoundException ex) {
// If EJB 3.1 API not present, simply ignore.
}
if (exceptionHandler != null) {
this.exceptionHandler = exceptionHandler;
}
else {
this.exceptionHandler = new SimpleAsyncUncaughtExceptionHandler();
}
this.advice = buildAdvice(executor, this.exceptionHandler);
this.pointcut = buildPointcut(asyncAnnotationTypes);
}
在这里主要是构建通知和切点，下面我们分别来看看怎么实现的：
buildAdvice:
protected Advice buildAdvice(Executor executor, AsyncUncaughtExceptionHandler exceptionHandler) {
return new AnnotationAsyncExecutionInterceptor(executor, exceptionHandler);
}
AnnotationAsyncExecutionInterceptor的父类实现了MethodInterceptor接口，我们来看看它重写的方法：
/**
* Intercept the given method invocation, submit the actual calling of the method to
* the correct task executor and return immediately to the caller.
* @param invocation the method to intercept and make asynchronous
* @return {@link Future} if the original method returns {@code Future}; {@code null}
* otherwise.
*/
@Override
public Object invoke(final MethodInvocation invocation) throws Throwable {
Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);
Method specificMethod = ClassUtils.getMostSpecificMethod(invocation.getMethod(), targetClass);
final Method userDeclaredMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);
//取@Async里的value属性对应Bean，如果没有值取名字为taskExecutor的Bean
AsyncTaskExecutor executor = determineAsyncExecutor(userDeclaredMethod);
if (executor == null) {
throw new IllegalStateException(
"No executor specified and no default executor set on AsyncExecutionInterceptor either");
}
Callable<Object> task = new Callable<Object>() {
@Override
public Object call() throws Exception {
try {
//异步执行本体方法
Object result = invocation.proceed();
if (result instanceof Future) {
return ((Future<?>) result).get();
}
}
catch (ExecutionException ex) {
handleError(ex.getCause(), userDeclaredMethod, invocation.getArguments());
}
catch (Throwable ex) {
handleError(ex, userDeclaredMethod, invocation.getArguments());
}
return null;
}
};
return doSubmit(task, executor, invocation.getMethod().getReturnType());
}
buildPointCut:
/**
* Calculate a pointcut for the given async annotation types, if any.
* @param asyncAnnotationTypes the async annotation types to introspect
* @return the applicable Pointcut object, or {@code null} if none
*/
protected Pointcut buildPointcut(Set<Class<? extends Annotation>> asyncAnnotationTypes) {
ComposablePointcut result = null;
for (Class<? extends Annotation> asyncAnnotationType : asyncAnnotationTypes) {
Pointcut cpc = new AnnotationMatchingPointcut(asyncAnnotationType, true);
Pointcut mpc = AnnotationMatchingPointcut.forMethodAnnotation(asyncAnnotationType);
if (result == null) {
result = new ComposablePointcut(cpc);
}
else {
result.union(cpc);
}
result = result.union(mpc);
}
return result;
}
在这里使用AnnotationMatchingPointcut，该切点会在有对应的annotation方法上切入相关的Advice，此处asyncAnnotationTypes对应的就是@Async
三、总结
Spring异步机制用到如下几种方式实现：
1）重写BeanPostProcessor来改变Bean的属性，在这里针对Advised或者ProxyFactory动态添加定义好的通知AsyncAnnotationAdvisor
2) 使用AOP的机制来，异步执行@Async标记的方法
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