Spring Circular Reference

Question

As far as I know, Spring resolves circular reference issue by exposing an ObjectFactory of each bean currently in creation.

The problem I feel confused is : Why not instantiate each bean at first, and then populate autowire field using Field.set(obj,val) , why bother to make it so complicated using cache and object factory.

Answer 1

Dependency resolution process

Circular dependencies

If you use predominantly constructor injection, it is possible to create an unresolvable circular dependency scenario.

For example: Class A requires an instance of class B through constructor injection, and class B requires an instance of class A through constructor injection. If you configure beans for classes A and B to be injected into each other, the Spring IoC container detects this circular reference at runtime, and throws a BeanCurrentlyInCreationException.

One possible solution is to edit the source code of some classes to be configured by setters rather than constructors. Alternatively, avoid constructor injection and use setter injection only. In other words, although it is not recommended, you can configure circular dependencies with setter injection.

Unlike the typical case (with no circular dependencies), a circular dependency between bean A and bean B forces one of the beans to be injected into the other prior to being fully initialized itself (a classic chicken/egg scenario).