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场景&原因

先上代码

package com.shi.cycleref;import org.springframework.scheduling.annotation.Async;import org.springframework.scheduling.annotation.EnableAsync;import org.springframework.stereotype.Component;import javax.annotation.Resource;/** * @author syz */@EnableAsync@Componentpublic class A {
       @Resource    private B b;    @Async    public void a () {
       }}

package com.shi.cycleref;import org.springframework.context.annotation.Lazy;import org.springframework.stereotype.Component;import javax.annotation.Resource;/** * @author syz */@Componentpublic class B {
       @Resource    private A a;}

org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name ‘a’: Bean with name ‘a’ has been injected into other beans [b] 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.

执行以上代码出现以上错误，去分析了一下步骤

1. 先实例化A，初始化A时发现依赖B，缓存A
2. 实例化B，初始化B时发现依赖A，缓存中取到A注入，B完成
3. 返回初始化A步骤把刚刚生成好的B注入，发现A用到@Async注解生成A的代理类，造成了B中注入的A是未被代理的类（不是最终版本）

解决方法

1. 在B类中A属性上加@Lazy注解，在使用A时才会注入A

package com.shi.cycleref;import org.springframework.context.annotation.Lazy;import org.springframework.stereotype.Component;import javax.annotation.Resource;/** * @author syz */@Componentpublic class B {
       @Resource    @Lazy    private A a;}

2. 在A类上使用@DependsOn注解，创建A时会判断是否有此注解，有则先去创建标明的类

package com.shi.cycleref;import org.springframework.context.annotation.DependsOn;import org.springframework.scheduling.annotation.Async;import org.springframework.scheduling.annotation.EnableAsync;import org.springframework.stereotype.Component;import javax.annotation.Resource;/** * @author syz */@EnableAsync@Component@DependsOn("b")public class A {
       {
           System.out.println("AAAAAAAAAAAAA");    }    @Resource    private B b;    @Async    public void a () {
       }}

注意

主要是一个初始化顺序的问题，A在B之前创建完毕则可避免此问题

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