Circular dependency occurs in Spring when two or more beans have dependencies on each other, forming a cycle. Resolving circular dependency in Spring can be done using the following methods:
- Use setter injection: One way to resolve circular dependency is by using setter injection. In this method, you declare a bean with a setter method for the circular dependency. Then you inject the other bean into this setter method.
- Use constructor injection with @Autowired: Another way to resolve circular dependency is by using constructor injection with the @Autowired annotation. This method requires that you have at least one of the beans as a prototype bean, and the other bean should be a singleton bean.
- Use @Lazy annotation: You can also use the @Lazy annotation to resolve circular dependency in Spring. This annotation delays the creation of the bean until it is requested by another bean. This method can help you break the circular dependency cycle.
- Redesign your architecture: If none of the above methods work, you may need to redesign your architecture. Consider splitting your beans into smaller, more modular components that do not have circular dependencies.
In summary, resolving circular dependency in Spring can be achieved through setter injection, constructor injection with @Autowired, using the @Lazy annotation, or redesigning your architecture.
Let me explain with an example.
Consider the following scenario where we have two classes, ClassA and ClassB, that depend on each other:
public class ClassA {
private ClassB b;
public ClassA(ClassB b) {
this.b = b;
}
}
public class ClassB {
private ClassA a;
public ClassB(ClassA a) {
this.a = a;
}
}
In this scenario, ClassA depends on ClassB, and ClassB depends on ClassA. This forms a circular dependency, and Spring cannot resolve it.
To resolve this circular dependency in Spring, we can use constructor injection with the @Autowired annotation. Here’s how we can modify the classes to achieve this:
public class ClassA {
private ClassB b;
@Autowired
public ClassA(ClassB b) {
this.b = b;
}
}
public class ClassB {
private ClassA a;
@Autowired
public ClassB(ClassA a) {
this.a = a;
}
}
In this modified scenario, we have added the @Autowired annotation to the constructors of both ClassA and ClassB. This tells Spring to inject the necessary dependencies when creating these classes.
By using constructor injection with @Autowired, Spring can resolve the circular dependency between ClassA and ClassB. When Spring creates an instance of ClassA, it injects an instance of ClassB into its constructor, which in turn injects an instance of ClassA into its constructor. This way, Spring can resolve the circular dependency between ClassA and ClassB without any issues.
Note that this is just one way to resolve circular dependency in Spring. There are other ways such as using setter injection, using the @Lazy annotation, or redesigning your architecture. The approach you choose will depend on your specific use case and requirements.