异常出现条件

1. 开启异步处理注解 @EnableAsync
2. 代码环境

@Service
public class AyncTestImpl implements AyncTest {@Autowiredprivate HelloServiceA helloServiceA;@Async@Overridepublic void sayHello() {helloServiceA.hello();}
}

@Service
public class HelloServiceA {@Autowiredprivate AyncTest ayncTest;public void hello(){System.out.println("hello A");}}

3. 加载顺序，这里我们得确保Spring首先实例化AyncTestImpl 然后在实例化HelloServiceA。，同一个文件夹下AyncTestImpl 在HelloServiceA 前面默认加载顺序就可以符合。
   
   DefaultListableBeanFactory的preInstantiateSingletons() 方法
   

出现如下异常

警告: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'ayncTestImpl': Bean with name 'ayncTestImpl' has been injected into other beans [helloServiceA] in its raw version as part of a circular reference, but has eventually been wrapped. This means that said other beans do not use the final version of the bean. This is often the result of over-eager type matching - consider using 'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.
Exception in thread "main" org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'ayncTestImpl': Bean with name 'ayncTestImpl' has been injected into other beans [helloServiceA] in its raw version as part of a circular reference, but has eventually been wrapped. This means that said other beans do not use the final version of the bean. This is often the result of over-eager type matching - consider using 'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:682)at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:540)at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:369)at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:283)at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:367)at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:905)at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:943)at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:591)at org.springframework.context.annotation.AnnotationConfigApplicationContext.(AnnotationConfigApplicationContext.java:108)at com.demo.Entrance.main(Entrance.java:41)

解释：： helloServiceA 注入的ayncTestImpl 不是最终的版本。我们知道ayncTestImpl的方法是需要进行异步执行，正常ayncTestImpl对象是没有这种功能的，要添加这种功能需要对ayncTestImpl对象进行代理，所以Spring有处理器对ayncTestImpl对象进行动态代理，使之具有异步方法功能。出现这个异常就是说helloServiceA 注入的ayncTestImpl的原始对象， 而Spring容器最终的aynnTestImpl的对象是进行代理之后具有异步功能的代理对象

解决方法

让Spring容器先完全的加载ayncTestImpl对象，容器注入ayncTestImpl代理对象之后再去，即可以在ayncTestImpl的注入对象加入@Lazy注解。

@Service
public class AyncTestImpl implements AyncTest {@Autowired@Lazyprivate HelloServiceA helloServiceA;@Async@Overridepublic void sayHello() {helloServiceA.hello();}
}

原理探究

设置Debug断点，我们直接看ayncTestImpl的Bean生命周期过程就行。

这里就不就Debug了，建议自己去Debug， 这里只总结出一个流程图，更容易接收

@Async增强时机与一般AOP增强时机的过程

总结

到这里，Async为什么会引发BeanCurrentlyInCreationException 就结束了，接着笔者还会出一篇博文， 探究@aync的增强原理，为什么我们开启了 @EnableAsync 注解，然后在方法上使用 @Async 就可以使用异步功能，以及如果异步方法出现了异常，Spring Async又提供了怎样获取异常处理扩展点呢？