@EnableAsync的使用、进阶、源码分析

@EnableAsync使用

基础使用

使用@EnableAsync开启异步切面，然后在异步调用的方法上加上@Asyc注解即可

@SpringBootApplication
@EnableAsync //开启异步切面
public class SpringdemoApplication {

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

}

@Service
public class AsyncTestServiceImpl implements AsyncTestService {

    @Async //异步
    @Override
    public void invokeAsyncTest01() {

        System.out.println(Thread.currentThread() + "运行了invokeAsyncTest01方法！");

    }

}

自定义异步注解

@Async注解是异步切面默认的异步注解，我们可以在@EnableAsync(annotation = AsyncCustom.class)开启异步切面时指定自定义的异步注解

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface AsyncCustom {
}

@SpringBootApplication
@EnableAsync(annotation = AsyncCustom.class)
public class SpringdemoApplication {

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

}

@Service
public class AsyncTestServiceImpl implements AsyncTestService {

    @AsyncCustom //异步
    @Override
    public void invokeAsyncTest01() {

        System.out.println(Thread.currentThread() + "运行了invokeAsyncTest01方法！");

    }

}

@EnableAsync进阶

线程池配置

配置默认线程池

当@Async注解的value没有指定线程池名称时，将会使用此线程池，不手动设置默认线程池，系统也会给你创建一个默认线程池（详细流程请看 线程池获取优先级）。

@Slf4j
@Component
public class AsyncConfig implements AsyncConfigurer {

	/**
	* 设置默认线程池
	**/
    @Override
    public Executor getAsyncExecutor() {

		//此处最好使用new ThreadPoolExecutor显示创建线程池，SimpleAsyncTaskExecutor没有复用线程
        SimpleAsyncTaskExecutor taskExecutor = new SimpleAsyncTaskExecutor();
        taskExecutor.setThreadNamePrefix("CustomAsync-Test-");

        return taskExecutor;
    }

}

@Service
public class AsyncTestServiceImpl implements AsyncTestService {

    @Async
    @Override
    public void invokeAsyncTest01() {

        System.out.println(Thread.currentThread() + "运行了invokeAsyncTest01方法！");

    }
}

指定线程池 （建议，根据业务进行线程池隔离）

当@Async注解的value有指定线程池名称时，将会使用容器中beanname=此value值的Executor线程池

@Configuration
public class TaskExecutorConfig {

    @Bean
    public Executor deleteFileExecutor() {

		//此处最好使用new ThreadPoolExecutor显示创建，SimpleAsyncTaskExecutor没有复用线程
        SimpleAsyncTaskExecutor taskExecutor = new SimpleAsyncTaskExecutor();
        taskExecutor.setThreadNamePrefix("delete-file-");
        return taskExecutor;
    }

    @Bean
    public Executor sendEmailExecutor() {

		//此处最好使用new ThreadPoolExecutor显示创建线程池，SimpleAsyncTaskExecutor没有复用线程
        SimpleAsyncTaskExecutor taskExecutor = new SimpleAsyncTaskExecutor();
        taskExecutor.setThreadNamePrefix("send-email-");
        return taskExecutor;
    }

}

@Service
public class AsyncTestServiceImpl implements AsyncTestService {

    @Async("deleteFileExecutor")
    @Override
    public void deleteFile() {

        System.out.println(Thread.currentThread() + "运行了deleteFile方法！");

    }

    @Async("sendEmailExecutor")
    @Override
    public void sendEmail() {

        System.out.println(Thread.currentThread() + "运行了sendEmail方法！");

    }

}

异步任务结果

只要是异步，一般都有可能用到需要返回结果的异步任务，当然@Async也支持异步结果返回，目前仅支持CompletableFuture、ListenableFuture、Future

CompletableFuture

@RestController
@RequestMapping("/testasync")
public class TestAsyncController {

    @Autowired
    private AsyncTestService asyncTestService;

    @GetMapping("/test02")
    public void test02() {

        CompletableFuture<String> completableFuture = asyncTestService.invokeAsyncTest02();

        completableFuture.thenAccept(System.out::println);

    }
 }

@Service
public class AsyncTestServiceImpl implements AsyncTestService {

    @Async
    @Override
    public CompletableFuture<String> invokeAsyncTest02() {

        System.out.println(Thread.currentThread() + "运行了invokeAsyncTest02方法！");

        return CompletableFuture.completedFuture("Hello world!");
    }
}

ListenableFuture

@RestController
@RequestMapping("/testasync")
public class TestAsyncController {

    @Autowired
    private AsyncTestService asyncTestService;

    @GetMapping("/test03")
    public void test03() {

        ListenableFuture<String> stringListenableFuture = asyncTestService.invokeAsyncTest03();

        stringListenableFuture.addCallback(System.out::println, System.out::println);

    }
}

@Service
public class AsyncTestServiceImpl implements AsyncTestService {

    @Async
    @Override
    public ListenableFuture<String> invokeAsyncTest03() {

        System.out.println(Thread.currentThread() + "运行了invokeAsyncTest03方法！");

        return new AsyncResult<String>("Hello World!");

    }
}

Future

@RestController
@RequestMapping("/testasync")
public class TestAsyncController {

    @Autowired
    private AsyncTestService asyncTestService;

    @GetMapping("/test04")
    public void test04() throws ExecutionException, InterruptedException {

        Future<String> future = asyncTestService.invokeAsyncTest04();

        String str = future.get();

        System.out.println(str);

    }
}

@Service
public class AsyncTestServiceImpl implements AsyncTestService {
    @Async
    @Override
    public Future<String> invokeAsyncTest04() {

        System.out.println(Thread.currentThread() + "运行了invokeAsyncTest04方法！");

        return new AsyncResult<>("Hello World!");

    }
}

Future、ListenableFuture、CompletableFuture区别

• Future为异步任务调用的结果

• ListenableFuture继承了Future，所以也为异步任务调用的结果，但是ListenableFuture还阔以添加两个回调函数，成功回调和异常回调

• CompletableFuture也继承了Future，所以也为异步任务调用的结果，但是CompletableFuture阔以对异步任务进行编排

异常处理器

当返回值是Future及其子类

此时，如果异步任务在执行时抛出异常时，异常先会存储在Future中并记录状态，当正真调用future.get()等获取结果函数时才会抛出异常。

@RestController
@RequestMapping("/testasync")
public class TestAsyncController {

    @Autowired
    private AsyncTestService asyncTestService;
    
    @GetMapping("/test04")
    public void test04() throws ExecutionException, InterruptedException {

        Future<String> future = asyncTestService.invokeAsyncTest04();
        
		//此时当当前线程获取结果时 才会抛出异常
        String str = future.get();

        System.out.println(str);

    }
}

@Service
public class AsyncTestServiceImpl implements AsyncTestService {

    @Async
    @Override
    public Future<String> invokeAsyncTest04() {

        System.out.println(Thread.currentThread() + "运行了invokeAsyncTest04方法！");

        if(true){
            throw new IllegalArgumentException("Hello sendEmailExecutor Exception！");
        }

        return new AsyncResult<>("Hello World!");

    }
}

当返回值是非Future

返回类型非Future时，任务发生异常将会调用异常处理器处理异常。异常处理器阔以AsyncConfigurer 实现类的getAsyncUncaughtExceptionHandler方法手动设置，如果未设置异常处理器，系统将会给你创建一个默认的SimpleAsyncUncaughtExceptionHandler异常处理器，此默认异常处理器异常处理器只对异常进行了日志输出

@Slf4j
@Component
public class AsyncConfig implements AsyncConfigurer {

    @Override
    public Executor getAsyncExecutor() {

        SimpleAsyncTaskExecutor taskExecutor = new SimpleAsyncTaskExecutor();
        taskExecutor.setThreadNamePrefix("CustomAsync-Test-");

        return taskExecutor;
    }

	/**
	* 当异步任务调用出现时将会调用此异常处理器 可在此记录日志，补偿机制等
	**/
    @Override
    public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {

        return (ex, method, params) -> {
            System.err.println("Unexpected exception occurred invoking async method: " + method + ":" + ex.getMessage());
        };

    }

}

@RestController
@RequestMapping("/testasync")
public class TestAsyncController {

    @Autowired
    private AsyncTestService asyncTestService;

    @GetMapping("/test06")
    public void test06() {

        asyncTestService.invokeAsyncTest06();

    }
}

@Service
public class AsyncTestServiceImpl implements AsyncTestService {

    @Async
    @Override
    public void invokeAsyncTest06() {

        System.out.println(Thread.currentThread() + "运行了invokeAsyncTest06方法！");

        throw new IllegalArgumentException("Hello Exception！");

    }
}

扩展异常处理器

原因

博主通过源码发现，异常处理器只能设置一个，且后续所有@Async使用的线程池全都只有走我们设置的默认异常处理器，如果我们根据业务划分了线程池，不同线程池的异常想走不同的处理逻辑，就只有在我们手动设置的异常处理器中进行逻辑判断，非常的不优雅。

博主的解决方案

1. 扩展@Async注解，添加exceptionHandler属性指定异常处理器AsyncUncaughtExceptionHandler 的容器名
2. 在设置AsyncConfigurer 实现类getAsyncUncaughtExceptionHandler方法设置一个自定义异常处理器，此处理器读取异常方法@Async的exceptionHandler属性值，然后获取到容器中名为exceptionHandler属性值的异常处理器
3. 如果能在容器找到给定容器名称的异常处理器，就走此异常处理器
4. 如果不能找到给定容器名称的处理器，就走默认异常处理器
5. 如果没有设置@Async的exceptionHandler属性值，也走默认异常处理器

方案实现

扩展@Async注解，添加@JokerAsync继承@Async，添加exceptionHandler属性

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Async
public @interface JokerAsync {

    @AliasFor(annotation = Async.class)
    String value() default "";

    String exceptionHandler() default "";
}

把AsyncConfigurer 实现类getAsyncUncaughtExceptionHandler方法设置一个自定义异常处理器，此处理器读取异常方法@Async的exceptionHandler属性值，然后获取到容器中名为exceptionHandler属性值的异常处理器

@Slf4j
@Component
public class AsyncConfig implements AsyncConfigurer {

    @Autowired(required = false)
    private Map<String, AsyncUncaughtExceptionHandler> exceptionHandlerMap = new HashMap<>();

    private final AsyncUncaughtExceptionHandler defaultExceptionHandler = new SimpleAsyncUncaughtExceptionHandler();

    @Override
    public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {

        return (ex, method, params) -> {

            String qualifier = getExceptionHandlerQualifier(method);

            AsyncUncaughtExceptionHandler exceptionHandler = null;

            if (Objects.nonNull(qualifier) && qualifier.length() > 0) {
                exceptionHandler = exceptionHandlerMap.get(qualifier);
            }

            if (Objects.isNull(exceptionHandler)) {
                exceptionHandler = defaultExceptionHandler;
            }

            exceptionHandler.handleUncaughtException(ex, method, params);

        };

    }

    protected String getExceptionHandlerQualifier(Method method) {

        JokerAsync async = AnnotatedElementUtils.findMergedAnnotation(method, JokerAsync.class);

        if (async == null) {
            async = AnnotatedElementUtils.findMergedAnnotation(method.getDeclaringClass(), JokerAsync.class);
        }

        return (async != null ? async.exceptionHandler() : null);

    }

}

测试示例代码

@Slf4j
@Component
public class DeleteFileAsyncUncaughtExceptionHandler implements AsyncUncaughtExceptionHandler {

    @Override
    public void handleUncaughtException(Throwable ex, Method method, Object... params) {
        log.error("DeleteFileAsyncUncaughtExceptionHandler Unexpected exception occurred invoking async method: " + method, ex);
    }

}

@Slf4j
@Component
public class SendFileAsyncUncaughtExceptionHandler implements AsyncUncaughtExceptionHandler {


    @Override
    public void handleUncaughtException(Throwable ex, Method method, Object... params) {
        log.error("SendFileAsyncUncaughtExceptionHandler Unexpected exception occurred invoking async method: " + method, ex);
    }

}

@Service
public class AsyncTestServiceImpl implements AsyncTestService {

    @JokerAsync(exceptionHandler = "deleteFileAsyncUncaughtExceptionHandler")
    @Override
    public void deleteFile() {

        System.out.println(Thread.currentThread() + "运行了deleteFile方法！");

        throw new IllegalArgumentException("Hello deleteFileExecutor Exception！");

    }

    @JokerAsync(exceptionHandler = "sendFileAsyncUncaughtExceptionHandler")
    @Override
    public void sendEmail() {

        System.out.println(Thread.currentThread() + "运行了sendEmail方法！");

        throw new IllegalArgumentException("Hello sendEmailExecutor Exception！");

    }

}

@RestController
@RequestMapping("/testasync")
public class TestAsyncController {

    @Autowired
    private AsyncTestService asyncTestService;

    @GetMapping("/sendEmail")
    public void sendEmail() {

        asyncTestService.sendEmail();

    }

    @GetMapping("/deleteFile")
    public void deleteFile() {

        asyncTestService.deleteFile();

    }
}

结果如下：不同的业务走不同的异常处理器

源码分析

首先咱们从@EnableAsync入口开始看起

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
//使用@Import 导入AsyncConfigurationSelector类到容器中
@Import(AsyncConfigurationSelector.class) 
public @interface EnableAsync {

	//自定义异步注解
	Class<? extends Annotation> annotation() default Annotation.class;
	
	//JDK代理 还是 CGLIB代理
	boolean proxyTargetClass() default false;

	AdviceMode mode() default AdviceMode.PROXY;

	int order() default Ordered.LOWEST_PRECEDENCE;

}

注意使用@Import注解导入的一般会实现ImportSelector 接口，则ImportSelector 中的selectImports方法返回的类的完全限定名数组中的类会被加入到容器中；如果是实现了ImportBeanDefinitionRegistrar接口，则会调用registerBeanDefinitions的方法

public interface ImportSelector {
	String[] selectImports(AnnotationMetadata importingClassMetadata);

	@Nullable
	default Predicate<String> getExclusionFilter() {
		return null;
	}

}

public interface ImportBeanDefinitionRegistrar {

	default void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry,
			BeanNameGenerator importBeanNameGenerator) {

		registerBeanDefinitions(importingClassMetadata, registry);
	}

	default void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
	}

}

继续看@EnableAsync使用@Import导入的AsyncConfigurationSelector类

public class AsyncConfigurationSelector extends AdviceModeImportSelector<EnableAsync> {

	private static final String ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME =
			"org.springframework.scheduling.aspectj.AspectJAsyncConfiguration";


	/**
	 * Returns {@link ProxyAsyncConfiguration} or {@code AspectJAsyncConfiguration}
	 * for {@code PROXY} and {@code ASPECTJ} values of {@link EnableAsync#mode()},
	 * respectively.
	 */
	@Override
	@Nullable
	public String[] selectImports(AdviceMode adviceMode) {
		switch (adviceMode) {
			//@EnableAsync mode属性默认为AdviceMode.PROXY 
			case PROXY:
				return new String[] {ProxyAsyncConfiguration.class.getName()};
			case ASPECTJ:
				return new String[] {ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME};
			default:
				return null;
		}
	}

}

看哈AsyncConfigurationSelector的父类AdviceModeImportSelector

/**
* 由于该类实现ImportSelector接口 所以会调用selectImports方法
**/
public abstract class AdviceModeImportSelector<A extends Annotation> implements ImportSelector {

	public static final String DEFAULT_ADVICE_MODE_ATTRIBUTE_NAME = "mode";

	protected String getAdviceModeAttributeName() {
		return DEFAULT_ADVICE_MODE_ATTRIBUTE_NAME;
	}

	//importingClassMetadata 是加了@Import注解的类的元信息
	@Override
	public final String[] selectImports(AnnotationMetadata importingClassMetadata) {
		Class<?> annType = GenericTypeResolver.resolveTypeArgument(getClass(), AdviceModeImportSelector.class);
		Assert.state(annType != null, "Unresolvable type argument for AdviceModeImportSelector");

		AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor(importingClassMetadata, annType);
		if (attributes == null) {
			throw new IllegalArgumentException(String.format(
					"@%s is not present on importing class '%s' as expected",
					annType.getSimpleName(), importingClassMetadata.getClassName()));
		}
		//得到加了@Import注解类上的mode属性值
		AdviceMode adviceMode = attributes.getEnum(getAdviceModeAttributeName());
		//模板方法 调用子类实现的selectImports方法得到需要导入到Spring容器中的类的
		String[] imports = selectImports(adviceMode);
		if (imports == null) {
			throw new IllegalArgumentException("Unknown AdviceMode: " + adviceMode);
		}
		return imports;
	}

	@Nullable
	protected abstract String[] selectImports(AdviceMode adviceMode);

}

由于@EnableAsync mode属性默认为AdviceMode.PROXY ，所以ProxyAsyncConfiguration类将会导入容器继续点进去看

@Configuration(proxyBeanMethods = false)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public class ProxyAsyncConfiguration extends AbstractAsyncConfiguration {

	//把异步后置处理器放入容器中
	@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");
		//异步后置处理器
		AsyncAnnotationBeanPostProcessor bpp = new AsyncAnnotationBeanPostProcessor();
		
		//把线程池和异常处理器放到后置处理器中
		bpp.configure(this.executor, this.exceptionHandler);
		
		//得到@EnableAsync中annotation的注解
		Class<? extends Annotation> customAsyncAnnotation = this.enableAsync.getClass("annotation");
		
		//自定义注解不等于默认值时 把自定义异步注解放入后置处理器中
		if (customAsyncAnnotation != AnnotationUtils.getDefaultValue(EnableAsync.class, "annotation")) {
			bpp.setAsyncAnnotationType(customAsyncAnnotation);
		}
		//设置动态代理方式
		bpp.setProxyTargetClass(this.enableAsync.getBoolean("proxyTargetClass"));
		
		bpp.setOrder(this.enableAsync.<Integer>getNumber("order"));
		return bpp;
	}

}

看哈ProxyAsyncConfiguration 的父类AbstractAsyncConfiguration

@Configuration(proxyBeanMethods = false)
public abstract class AbstractAsyncConfiguration implements ImportAware {

	@Nullable
	protected AnnotationAttributes enableAsync;

	@Nullable
	protected Supplier<Executor> executor;

	@Nullable
	protected Supplier<AsyncUncaughtExceptionHandler> exceptionHandler;

	//importMetadata 是加了@Import注解的类的元信息
	@Override
	public void setImportMetadata(AnnotationMetadata importMetadata) {
		//@EnableAsync的注解属性设置给enableAsync属性
		this.enableAsync = AnnotationAttributes.fromMap(
				importMetadata.getAnnotationAttributes(EnableAsync.class.getName(), false));
		if (this.enableAsync == null) {
			throw new IllegalArgumentException(
					"@EnableAsync is not present on importing class " + importMetadata.getClassName());
		}
	}

	/**
	* 配置默认线程池 默认异常处理器
	**/
	@Autowired(required = false)
	void setConfigurers(Collection<AsyncConfigurer> configurers) {
		if (CollectionUtils.isEmpty(configurers)) {
			return;
		}
		if (configurers.size() > 1) {
			throw new IllegalStateException("Only one AsyncConfigurer may exist");
		}
		AsyncConfigurer configurer = configurers.iterator().next();
		this.executor = configurer::getAsyncExecutor;
		this.exceptionHandler = configurer::getAsyncUncaughtExceptionHandler;
	}

}

public interface AsyncConfigurer {
	
	//配置异步线程池
	@Nullable
	default Executor getAsyncExecutor() {
		return null;
	}

	//配置异步异常处理器
	@Nullable
	default AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
		return null;
	}

}

上述代码表明 把@EnableAsync注解的属性解析了设置到了AsyncAnnotationBeanPostProcessor后置处理器中，还有AsyncConfigurer配置的线程池和异常处理器也设置到了后置处理中，现在我们继续看AsyncAnnotationBeanPostProcessor后置处理器的代码

public class AsyncAnnotationBeanPostProcessor extends AbstractBeanFactoryAwareAdvisingPostProcessor {

	public static final String DEFAULT_TASK_EXECUTOR_BEAN_NAME =
			AnnotationAsyncExecutionInterceptor.DEFAULT_TASK_EXECUTOR_BEAN_NAME;

	//默认线程池
	@Nullable
	private Supplier<Executor> executor;

	//异常处理器
	@Nullable
	private Supplier<AsyncUncaughtExceptionHandler> exceptionHandler;

	//异步注解
	@Nullable
	private Class<? extends Annotation> asyncAnnotationType;

	public AsyncAnnotationBeanPostProcessor() {
		setBeforeExistingAdvisors(true);
	}
	
	public void configure(
			@Nullable Supplier<Executor> executor, @Nullable Supplier<AsyncUncaughtExceptionHandler> exceptionHandler) {

		this.executor = executor;
		this.exceptionHandler = exceptionHandler;
	}

	public void setExecutor(Executor executor) {
		this.executor = SingletonSupplier.of(executor);
	}
	public void setExceptionHandler(AsyncUncaughtExceptionHandler exceptionHandler) {
		this.exceptionHandler = SingletonSupplier.of(exceptionHandler);
	}

	public void setAsyncAnnotationType(Class<? extends Annotation> asyncAnnotationType) {
		Assert.notNull(asyncAnnotationType, "'asyncAnnotationType' must not be null");
		this.asyncAnnotationType = asyncAnnotationType;
	}

	/**
	*  由于父类实现了BeanFactoryAware接口 在实例初始化时会被调用
	**/
	@Override
	public void setBeanFactory(BeanFactory beanFactory) {
		super.setBeanFactory(beanFactory);
		/**
		* Advice：通知，标识逻辑织入的位置（增强代码调用的地方）。
		* PointCut：切入点，标识对什么方法进入代理（判断哪个方法能被增强）;
		* Advisor：通知器，是通知与切入点的集合（一般里面持有一个Advice和一个PointCut，用来标识一个切面增强）。
		**/
		//我们阔以看到此处创建了一个通知器 把线程池和异常处理器传进去 
		AsyncAnnotation  advisor = new AsyncAnnotationAdvisor(this.executor, this.exceptionHandler);
		if (this.asyncAnnotationType != null) {
			advisor.setAsyncAnnotationType(this.asyncAnnotationType);
		}
		//把类工厂传入通知器中
		advisor.setBeanFactory(beanFactory);
		//把通知器赋给本类的成员变量
		this.advisor = advisor;
	}

}

上诉代码主要是把增强的advisor 类创建好并复制给了本类成员变量，
下面我们继续看此类的父类AbstractAdvisingBeanPostProcessor，应为此类实现了BeanPostProcessor 接口，所以初始化完后肯定会调用postProcessAfterInitialization方法

public abstract class AbstractAdvisingBeanPostProcessor extends ProxyProcessorSupport implements BeanPostProcessor {

	@Nullable
	protected Advisor advisor;

	protected boolean beforeExistingAdvisors = false;

	private final Map<Class<?>, Boolean> eligibleBeans = new ConcurrentHashMap<>(256);

	public void setBeforeExistingAdvisors(boolean beforeExistingAdvisors) {
		this.beforeExistingAdvisors = beforeExistingAdvisors;
	}


	@Override
	public Object postProcessBeforeInitialization(Object bean, String beanName) {
		return bean;
	}

	@Override
	public Object postProcessAfterInitialization(Object bean, String beanName) {
		if (this.advisor == null || bean instanceof AopInfrastructureBean) {
			// Ignore AOP infrastructure such as scoped proxies.
			return bean;
		}

		//如果被代理过 直接把Advisor加入到代理里中的Advisor列表中
		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;
			}
		}

		//如果没被代理过但是需要被代理的类 创建代理并直接加入到增强Advisor加入的Advisor列表中，并返回代理类
		if (isEligible(bean, beanName)) {
			ProxyFactory proxyFactory = prepareProxyFactory(bean, beanName);
			if (!proxyFactory.isProxyTargetClass()) {
				evaluateProxyInterfaces(bean.getClass(), proxyFactory);
			}
			proxyFactory.addAdvisor(this.advisor);
			customizeProxyFactory(proxyFactory);

			// Use original ClassLoader if bean class not locally loaded in overriding class loader
			ClassLoader classLoader = getProxyClassLoader();
			if (classLoader instanceof SmartClassLoader && classLoader != bean.getClass().getClassLoader()) {
				classLoader = ((SmartClassLoader) classLoader).getOriginalClassLoader();
			}
			return proxyFactory.getProxy(classLoader);
		}

		// No proxy needed.
		return bean;
	}

	protected boolean isEligible(Object bean, String beanName) {
		return isEligible(bean.getClass());
	}

	//判断此类是否需要代理
	protected boolean isEligible(Class<?> targetClass) {
		Boolean eligible = this.eligibleBeans.get(targetClass);
		if (eligible != null) {
			return eligible;
		}
		if (this.advisor == null) {
			return false;
		}
		eligible = AopUtils.canApply(this.advisor, targetClass);
		this.eligibleBeans.put(targetClass, eligible);
		return eligible;
	}

	protected ProxyFactory prepareProxyFactory(Object bean, String beanName) {
		ProxyFactory proxyFactory = new ProxyFactory();
		proxyFactory.copyFrom(this);
		proxyFactory.setTarget(bean);
		return proxyFactory;
	}

	protected void customizeProxyFactory(ProxyFactory proxyFactory) {
	}

}

上述代码可以知道，只是把增强的advisor 放入代理类中，所以我们只需要看advisor 中的增强方法就知道增强的代码逻辑。我们来看advisor 成员的实现类AsyncAnnotationAdvisor，而AsyncAnnotationAdvisor是Advisor的实现类。而Advisor实现类一般会包含一般里面持有一个Advice和一个PointCut类，而Advice的子类MethodInterceptor的invoke方法就是代理的主要增强代码实现的地方

	* Advice：通知，标识逻辑织入的位置（增强代码调用的地方）。
	* PointCut：切入点，标识对什么方法进入代理（判断哪个方法能被增强）;
	* Advisor：通知器，是通知与切入点的集合（一般里面持有一个Advice和一个PointCut，用来标识一个切面增强）。

public class AsyncAnnotationAdvisor extends AbstractPointcutAdvisor implements BeanFactoryAware {

	private Advice advice;

	private Pointcut pointcut;

	public AsyncAnnotationAdvisor() {
		this((Supplier<Executor>) null, (Supplier<AsyncUncaughtExceptionHandler>) null);
	}

	public AsyncAnnotationAdvisor(
			@Nullable Executor executor, @Nullable AsyncUncaughtExceptionHandler exceptionHandler) {

		this(SingletonSupplier.ofNullable(executor), SingletonSupplier.ofNullable(exceptionHandler));
	}

	@SuppressWarnings("unchecked")
	public AsyncAnnotationAdvisor(
			@Nullable Supplier<Executor> executor, @Nullable Supplier<AsyncUncaughtExceptionHandler> exceptionHandler) {

		Set<Class<? extends Annotation>> asyncAnnotationTypes = new LinkedHashSet<>(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.
		}
		//通知实现
		this.advice = buildAdvice(executor, exceptionHandler);
		//切入点实现
		this.pointcut = buildPointcut(asyncAnnotationTypes);
	}

	public void setAsyncAnnotationType(Class<? extends Annotation> asyncAnnotationType) {
		Assert.notNull(asyncAnnotationType, "'asyncAnnotationType' must not be null");
		Set<Class<? extends Annotation>> asyncAnnotationTypes = new HashSet<>();
		asyncAnnotationTypes.add(asyncAnnotationType);
		this.pointcut = buildPointcut(asyncAnnotationTypes);
	}

	@Override
	public void setBeanFactory(BeanFactory beanFactory) {
		if (this.advice instanceof BeanFactoryAware) {
			((BeanFactoryAware) this.advice).setBeanFactory(beanFactory);
		}
	}


	@Override
	public Advice getAdvice() {
		return this.advice;
	}

	@Override
	public Pointcut getPointcut() {
		return this.pointcut;
	}

	/**
	* 通知的实现类
	**/
	protected Advice buildAdvice(
			@Nullable Supplier<Executor> executor, @Nullable Supplier<AsyncUncaughtExceptionHandler> exceptionHandler) {
		//核心通知类
		AnnotationAsyncExecutionInterceptor interceptor = new AnnotationAsyncExecutionInterceptor(null);
		interceptor.configure(executor, exceptionHandler);
		return interceptor;
	}

	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 = new AnnotationMatchingPointcut(null, asyncAnnotationType, true);
			if (result == null) {
				result = new ComposablePointcut(cpc);
			}
			else {
				result.union(cpc);
			}
			result = result.union(mpc);
		}
		return (result != null ? result : Pointcut.TRUE);
	}

}

上面代码可以知道核心通知的实现类是AnnotationAsyncExecutionInterceptor，那就继续AnnotationAsyncExecutionInterceptor代码

public class AnnotationAsyncExecutionInterceptor extends AsyncExecutionInterceptor {

	public AnnotationAsyncExecutionInterceptor(@Nullable Executor defaultExecutor) {
		super(defaultExecutor);
	}

	public AnnotationAsyncExecutionInterceptor(@Nullable Executor defaultExecutor, AsyncUncaughtExceptionHandler exceptionHandler) {
		super(defaultExecutor, exceptionHandler);
	}

	@Override
	@Nullable
	protected String getExecutorQualifier(Method method) {
		// Maintainer's note: changes made here should also be made in
		// AnnotationAsyncExecutionAspect#getExecutorQualifier
		Async async = AnnotatedElementUtils.findMergedAnnotation(method, Async.class);
		if (async == null) {
			async = AnnotatedElementUtils.findMergedAnnotation(method.getDeclaringClass(), Async.class);
		}
		return (async != null ? async.value() : null);
	}

}

没有看到我们需要的invoke方法，继续看父类AsyncExecutionInterceptor

public class AsyncExecutionInterceptor extends AsyncExecutionAspectSupport implements MethodInterceptor, Ordered {

	public AsyncExecutionInterceptor(@Nullable Executor defaultExecutor) {
		super(defaultExecutor);
	}

	public AsyncExecutionInterceptor(@Nullable Executor defaultExecutor, AsyncUncaughtExceptionHandler exceptionHandler) {
		super(defaultExecutor, exceptionHandler);
	}

	@Override
	@Nullable
	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);
		
		//通过方法上的@Async注解里的value参数 value参数就是线程池Executor放入Spring容器的名称 ********
		AsyncTaskExecutor executor = determineAsyncExecutor(userDeclaredMethod);
		if (executor == null) {
			throw new IllegalStateException(
					"No executor specified and no default executor set on AsyncExecutionInterceptor either");
		}

		//把任务调用封装成callable方法  ****************
		Callable<Object> task = () -> {
			try {
				Object result = invocation.proceed();
				if (result instanceof Future) {
					return ((Future<?>) result).get();
				}
			}
			//如果出现了异常 走异常处理器
			catch (ExecutionException ex) {
				handleError(ex.getCause(), userDeclaredMethod, invocation.getArguments());
			}
			catch (Throwable ex) {
				handleError(ex, userDeclaredMethod, invocation.getArguments());
			}
			return null;
		};
		
		//把callable 线程池 和 方法返回类型一同传到doSubmit方法 *************
		return doSubmit(task, executor, invocation.getMethod().getReturnType());
	}

	@Nullable
	protected String getExecutorQualifier(Method method) {
		return null;
	}
	
	/**
	* 如果从父类方法获取不到线程池 就返回一个默认线程池new SimpleAsyncTaskExecutor()
	**/
	@Override
	@Nullable
	protected Executor getDefaultExecutor(@Nullable BeanFactory beanFactory) {
		Executor defaultExecutor = super.getDefaultExecutor(beanFactory);
		return (defaultExecutor != null ? defaultExecutor : new SimpleAsyncTaskExecutor());
	}

	@Override
	public int getOrder() {
		return Ordered.HIGHEST_PRECEDENCE;
	}

}

我们会发现获取线程池方法和正真调用方法的doSubmit方法都是在父类AsyncExecutionAspectSupport中，继续看AsyncExecutionAspectSupport代码

public abstract class AsyncExecutionAspectSupport implements BeanFactoryAware {

	public static final String DEFAULT_TASK_EXECUTOR_BEAN_NAME = "taskExecutor";


	protected final Log logger = LogFactory.getLog(getClass());

	private final Map<Method, AsyncTaskExecutor> executors = new ConcurrentHashMap<>(16);

	private SingletonSupplier<Executor> defaultExecutor;

	private SingletonSupplier<AsyncUncaughtExceptionHandler> exceptionHandler;

	@Nullable
	private BeanFactory beanFactory;

	public AsyncExecutionAspectSupport(@Nullable Executor defaultExecutor) {
		//默认线程池 
		this.defaultExecutor = new SingletonSupplier<>(defaultExecutor, () -> getDefaultExecutor(this.beanFactory));
		//默认异常处理器
		this.exceptionHandler = SingletonSupplier.of(SimpleAsyncUncaughtExceptionHandler::new);
	}

	public AsyncExecutionAspectSupport(@Nullable Executor defaultExecutor, AsyncUncaughtExceptionHandler exceptionHandler) {
		//默认线程池 
		this.defaultExecutor = new SingletonSupplier<>(defaultExecutor, () -> getDefaultExecutor(this.beanFactory));
		//默认异常处理器
		this.exceptionHandler = SingletonSupplier.of(exceptionHandler);
	}

	public void configure(@Nullable Supplier<Executor> defaultExecutor,
			@Nullable Supplier<AsyncUncaughtExceptionHandler> exceptionHandler) {
		//默认线程池
		this.defaultExecutor = new SingletonSupplier<>(defaultExecutor, () -> getDefaultExecutor(this.beanFactory));
		//默认异常处理器
		this.exceptionHandler = new SingletonSupplier<>(exceptionHandler, SimpleAsyncUncaughtExceptionHandler::new);
	}

	public void setExecutor(Executor defaultExecutor) {
		this.defaultExecutor = SingletonSupplier.of(defaultExecutor);
	}

	public void setExceptionHandler(AsyncUncaughtExceptionHandler exceptionHandler) {
		this.exceptionHandler = SingletonSupplier.of(exceptionHandler);
	}

	@Override
	public void setBeanFactory(BeanFactory beanFactory) {
		this.beanFactory = beanFactory;
	}

	/**
	* 获取@Async注释方法使用的线程池
	**/
	@Nullable
	protected AsyncTaskExecutor determineAsyncExecutor(Method method) {
		//先从缓存中取
		AsyncTaskExecutor executor = this.executors.get(method);
		//没有在从容器中找
		if (executor == null) {
			Executor targetExecutor;
			//得到此方法中@Async属性value的值 即  容器中线程池的Bean名称
			String qualifier = getExecutorQualifier(method);
			//如果设置了value值 就从容器中获取
			if (StringUtils.hasLength(qualifier)) {
				targetExecutor = findQualifiedExecutor(this.beanFactory, qualifier);
			}
			//如果没有设置value值 就获取AsyncConfigurer配置的默认线程池 如果没有就从容器中获取TaskExecutor的实现类，如果有多个TaskExecutor实现类，就取容器bean名称为“taskExecutor”的容Bean类
			else {
				targetExecutor = this.defaultExecutor.get();
			}
			if (targetExecutor == null) {
				return null;
			}
			executor = (targetExecutor instanceof AsyncListenableTaskExecutor ?
					(AsyncListenableTaskExecutor) targetExecutor : new TaskExecutorAdapter(targetExecutor));
			//放入缓存中
			this.executors.put(method, executor);
		}
		return executor;
	}

	@Nullable
	protected Executor getDefaultExecutor(@Nullable BeanFactory beanFactory) {
		if (beanFactory != null) {
			try {
				//先获取容器中TaskExecutor的实现类
				return beanFactory.getBean(TaskExecutor.class);
			}
			catch (NoUniqueBeanDefinitionException ex) {
				logger.debug("Could not find unique TaskExecutor bean. " +
						"Continuing search for an Executor bean named 'taskExecutor'", ex);
				try {
				//如果有多个就取名称DEFAULT_TASK_EXECUTOR_BEAN_NAME的Executor容器类
					return beanFactory.getBean(DEFAULT_TASK_EXECUTOR_BEAN_NAME, Executor.class);
				}
				catch (NoSuchBeanDefinitionException ex2) {
					if (logger.isInfoEnabled()) {
						logger.info("More than one TaskExecutor bean found within the context, and none is named " +
								"'taskExecutor'. Mark one of them as primary or name it 'taskExecutor' (possibly " +
								"as an alias) in order to use it for async processing: " + ex.getBeanNamesFound());
					}
				}
			}
			//如果容器中没有TaskExecutor的实现类 取名称DEFAULT_TASK_EXECUTOR_BEAN_NAME的Executor容器类
			catch (NoSuchBeanDefinitionException ex) {
				logger.debug("Could not find default TaskExecutor bean. " +
						"Continuing search for an Executor bean named 'taskExecutor'", ex);
				try {
					return beanFactory.getBean(DEFAULT_TASK_EXECUTOR_BEAN_NAME, Executor.class);
				}
				catch (NoSuchBeanDefinitionException ex2) {
					logger.info("No task executor bean found for async processing: " +
							"no bean of type TaskExecutor and no bean named 'taskExecutor' either");
				}
				// Giving up -> either using local default executor or none at all...
			}
		}
		//走完所有都没取到 线程池  那么就返回null 子类中会判断如果返回null 将new出一个默认线程池
		return null;
	}

	@Nullable
	protected Object doSubmit(Callable<Object> task, AsyncTaskExecutor executor, Class<?> returnType) {
		//如果返回类型是CompletableFuture及其子类 
		if (CompletableFuture.class.isAssignableFrom(returnType)) {
			return CompletableFuture.supplyAsync(() -> {
				try {
					return task.call();
				}
				catch (Throwable ex) {
					throw new CompletionException(ex);
				}
			}, executor);
		}
		//如果返回类型是ListenableFuture及其子类 
		else if (ListenableFuture.class.isAssignableFrom(returnType)) {
			return ((AsyncListenableTaskExecutor) executor).submitListenable(task);
		}
		//如果返回类型是Future及其子类 
		else if (Future.class.isAssignableFrom(returnType)) {
			return executor.submit(task);
		}
		//如果返回类型是其他
		else {
			executor.submit(task);
			return null;
		}
	}

	/**
	* 异常处理器
	**/
	protected void handleError(Throwable ex, Method method, Object... params) throws Exception {
		//如果返回类型是Future及其子类 发生异常 则直接丢出异常
		if (Future.class.isAssignableFrom(method.getReturnType())) {
			ReflectionUtils.rethrowException(ex);
		}
		//否则 则走异常处理器
		else {
			// Could not transmit the exception to the caller with default executor
			try {
				this.exceptionHandler.obtain().handleUncaughtException(ex, method, params);
			}
			catch (Throwable ex2) {
				logger.warn("Exception handler for async method '" + method.toGenericString() +
						"' threw unexpected exception itself", ex2);
			}
		}
	}

}

到此为止，源码已经分析的差不多了，我们阔以得出几个重点：

• AsyncConfigurer实现类可以设置默认线程池和默认异常处理器
• @Async的value是支持指定线程池
• @Async是支持全局异常处理器
• @Async注解的方法是可以支持返回类型为CompletableFuture、ListenableFuture、Future

总结

线程池获取优先级

当@Async中value值没有指定线程池

• 首先使用 AsyncConfigurer类中配置的默认线程池
• 如果没有配置AsyncConfigurer类，那么将使用容器TaskExecutor的实现类
• 如果容器中有多个TaskExecutor个实现类，将会使用beanname=”taskExecutor”的Executor实现类
• 如果容器中没有有TaskExecutor实现类，将会使用beanname=”taskExecutor”的Executor实现类
• 如果容器中没有beanname=”taskExecutor”的Executor实现类，将会new出一个SimpleAsyncTaskExecutor线程池

/最好使用new ThreadPoolExecutor显示创建线程池，SimpleAsyncTaskExecutor没有复用线程

当@Async中value值指定了线程池beanname，可以根据业务进行线程池级别隔离

• 取出容器中beanname=（@Async注解value值）的Executor实现类

如果没有取到相应的线程池，比如beanname写错导致取不到相应线程池将会抛出异常

异常处理器

返回类型为Future及其子类时

• 直接抛出异常

返回类型不是Future及其子类

• 当AsyncConfigurer设置了默认异常处理器，则走此异常处理器
• 如果没有设置AsyncConfigurer异常处理器，则走SimpleAsyncUncaughtExceptionHandler异常处理器，此处理器是直接打印日志

方法返回类型

CompletableFuture及其子类

//org.springframework.aop.interceptor.AsyncExecutionInterceptor#invoke
		Callable<Object> task = () -> {
			try {
				//@Async注释的方法调用
				Object result = invocation.proceed();
				//如果是Future类型 调用get获取结果值
				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;
		};
//org.springframework.aop.interceptor.AsyncExecutionAspectSupport#doSubmit
		if (CompletableFuture.class.isAssignableFrom(returnType)) {
		//@Async注释的方法返回类型如果为CompletableFuture及其子类
		//就使用线程池执行并封装成CompletableFuture返回
			return CompletableFuture.supplyAsync(() -> {
				try {
					return task.call();
				}
				catch (Throwable ex) {
					throw new CompletionException(ex);
				}
			}, executor);
		}

ListenableFuture及其子类

//org.springframework.aop.interceptor.AsyncExecutionInterceptor#invoke
		Callable<Object> task = () -> {
			try {
				//@Async注释的方法调用
				Object result = invocation.proceed();
				//如果是Future类型 调用get获取结果值
				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;
		};
//org.springframework.aop.interceptor.AsyncExecutionAspectSupport#doSubmit
		if (ListenableFuture.class.isAssignableFrom(returnType)) {
		//@Async注释的方法返回类型如果为ListenableFuture及其子类
		//就使用线程池执行并返回ListenableFuture
			return ((AsyncListenableTaskExecutor) executor).submitListenable(task);
		}

注意ListenableFuture.addCallback()添加回调函数时，如果异步任务还未执行完成，则回调函数由异步任务线程执行，如果异步任务已经执行完成，则是当前掉addCallback函数的线程调用回调函数

Future及其子类

//org.springframework.aop.interceptor.AsyncExecutionInterceptor#invoke
		Callable<Object> task = () -> {
			try {
				//@Async注释的方法调用
				Object result = invocation.proceed();
				//如果是Future类型 调用get获取结果值
				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;
		};
//org.springframework.aop.interceptor.AsyncExecutionAspectSupport#doSubmit
		if (Future.class.isAssignableFrom(returnType)) {
		//@Async注释的方法返回类型如果为Future及其子类
		//就使用线程池执行并返回Future
			return executor.submit(task);
		}

其他

源码分析

//org.springframework.aop.interceptor.AsyncExecutionInterceptor#invoke
		Callable<Object> task = () -> {
			try {
				//@Async注释的方法调用
				Object result = invocation.proceed();
				//如果是Future类型 调用get获取结果值
				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;
		};
//org.springframework.aop.interceptor.AsyncExecutionAspectSupport#doSubmit
		//@Async注释的方法返回类型如果是非Future
		//使用线程池执行后 直接返回null
		executor.submit(task);
		return null;

当返回值为void时无返回值示例

@RestController
@RequestMapping("/testasync")
public class TestAsyncController {

    @Autowired
    private AsyncTestService asyncTestService;

    @GetMapping("/test05")
    public void test05() {

        asyncTestService.invokeAsyncTest05();

    }
}

@Service
public class AsyncTestServiceImpl implements AsyncTestService {

    @Async
    @Override
    public void invokeAsyncTest05() {

        System.out.println(Thread.currentThread() + "运行了invokeAsyncTest05方法！");

    }
}

当返回值为非Futute类型示例

• 返回的结果为空，如果要异步结果，请用Future封装返回结果

@RestController
@RequestMapping("/testasync")
public class TestAsyncController {

    @Autowired
    private AsyncTestService asyncTestService;

    @GetMapping("/test07")
    public void test07() {

		//永远为null 如果要异步结果 请用Future封装返回结果
        List<String> result = asyncTestService.invokeAsyncTest07();

        System.out.println(result);

    }
}

@Service
public class AsyncTestServiceImpl implements AsyncTestService {

    @Async
    @Override
    public List<String> invokeAsyncTest07() {

        System.out.println(Thread.currentThread() + "invokeAsyncTest07！");

        List<String> result = Arrays.asList("Hello World1", "Hello World2");

        return result;
    }
    
}

思考

• 容器中beanname=”taskExecutor”的默认线程池是何时注入容器中的
• ListenableFuture的子类ListenableFutureTask的addCallback()添加的回调函数是被哪个线程调用的