Cyclic dependencies in spring boot

A cyclical dependency occurs in Java when two classes or two modules depend on each other, thus forming a cycle.

Suppose we have two beans A and B which depend on each other as shown in the example below:

@Component
public class A{
    private final B b;
    public A(B b){
        this.b = b;
    }
}

@Component
public class B{
    private final A a;
    public B(A a){
        this.a = a;
    }
}

When running your project, you will get the following error:

Relying upon circular references is discouraged and they are prohibited by default. Update your application to remove the dependency cycle between beans. As a last resort, it may be possible to break the cycle automatically by setting spring.main.allow-circular-references to true.

So, to resolve this cyclic dependency, we have four solutions:

• Refactor code to separate responsibilities.
• Use intermediate classes or interfaces.
• Apply dependency injection via methods (setter).
• Use annotations like @lazy to delay initialization.

In our case, we will use the fourth solution which is just to use the annotation @lazy as shown in the example below:

@Component
public class A{
    private final B b;
    public A(@Lazy B b){
        this.b = b;
    }
}

@Component
public class B{
    private final A a;
    public B(A a){
        this.a = a;
    }
}

And there we are, we are now out of this cycle :)

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