Circular Dependency in spring bean

1. What Is a Circular Dependency?

It happens when a bean A depends on another bean B, and the bean B depends on the bean A as well:

Bean A → Bean B → Bean A

Of course, we could have more beans implied:

Bean A → Bean B → Bean C → Bean D → Bean E → Bean A


Circular dependency is a design smell, either fix it or use @Lazy for the dependency which causes problem to workaround it.

@Component
public class CircularDependencyA {

    private CircularDependencyB circB;

    @Autowired
    public CircularDependencyA(CircularDependencyB circB) {
        this.circB = circB;
    }
}

@Component
public class CircularDependencyB {

    private CircularDependencyA circA;

    @Autowired
    public CircularDependencyB(CircularDependencyA circA) {
        this.circA = circA;
    }
}


Solution
Use @Lazy


A simple way to break the cycle is saying Spring to initialize one of the beans lazily. 


@Component
public class CircularDependencyA {

    private CircularDependencyB circB;

    @Autowired
    public CircularDependencyA(@Lazy CircularDependencyB circB) {
        this.circB = circB;
    }

}