Requested bean is currently in creation: Is there an unresolvable circular reference?

spring容器初始化报错：循环依赖，错误信息如下：

Requested bean is currently in creation: Is there an unresolvable circular reference?

与网上其他人A->B->C->A循环调用的情况不同，我这里是同一个类A，用@Service注解做了定义，又在其他地方用@Bean做了重复申明导致。

如下

@Service

class A {

}

class B {

@Bean

public A a() {

　　　　return new A();

　 }

}