Question

What is circular dependency in spring and how to solve it?

package com.circularBean.problem;

 

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.stereotype.Component;

 

@Component

public class A{

 

private B beanB;

 

@Autowired

public A(B beanB) {

this.beanB = beanB;

}

 

@Override

public String toString() {

return beanB.getClass().getSimpleName() + " from " + this.getClass().getSimpleName();

}

 

}

 

package com.circularBean.problem;

 

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.stereotype.Component;

 

@Component

public class B {

 

private A beanA;

 

@Autowired

public B(A beanA) {

this.beanA = beanA;

}

 

@Override

public String toString() {

return beanA.getClass().getSimpleName() + " from " + this.getClass().getSimpleName();

 

}

 

}

 

package com.circularBean.problem;

 

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

 

public class CircularBeanMain {

 

public static void main(String[] args) {

ApplicationContext applicationContext = new ClassPathXmlApplicationContext(new String[] { "resources/app-context.xml" });

A beanA = applicationContext.getBean(A.class);

B beanB = applicationContext.getBean(B.class);

System.out.println(beanA);

System.out.println(beanB);

}

 

}

 

Got Exception:- Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'b' defined in file [/home/ws/test/bin/com/circularBean/problem/B.class]: Unsatisfied dependency expressed through constructor argument with index 0 of type [com.circularBean.problem.A]: : Error creating bean with name 'a' defined in file [/home/ws/test/bin/com/circularBean/problem/A.class]: Unsatisfied dependency expressed through constructor argument with index 0 of type [com.circularBean.problem.B]: : Error creating bean with name 'b': Requested bean is currently in creation: Is there an unresolvable circular reference?; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'b': Requested bean is currently in creation: Is there an unresolvable circular reference?; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'a' defined in file [/home/ws/test/bin/com/circularBean/problem/A.class]: Unsatisfied dependency expressed through constructor argument with index 0 of type [com.circularBean.problem.B]: : Error creating bean with name 'b': Requested bean is currently in creation: Is there an unresolvable circular reference?; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'b': Requested bean is currently in creation: Is there an unresolvable circular reference?

Answer 1

To resolve circular bean references follow the following steps:

 Step1: - Make default constuctor 

 Step2: - Use setter method for injecting bean.

 

For more you see the following example:

 

package com.circularBean;

 

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.stereotype.Component;

 

@Component

public class BeanA{

 

private BeanB beanB;

 

public BeanA() {

}

 

@Autowired

public void setBeanB(BeanB beanB) {

this.beanB = beanB;

}

 

@Override

public String toString() {

return beanB.getClass().getSimpleName() + " from " + this.getClass().getSimpleName();

}

 

}

 

package com.circularBean;

 

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.stereotype.Component;

 

@Component

public class BeanB {

 

private BeanA beanA;

 

public BeanB() {

}

 

@Autowired

public void setBeanA(BeanA beanA) {

this.beanA = beanA;

}

 

@Override

public String toString() {

return beanA.getClass().getSimpleName() + " from " + this.getClass().getSimpleName();

 

}

 

}

 

package com.circularBean;

 

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

 

public class CircularBeanMain {

 

public static void main(String[] args) {

ApplicationContext applicationContext = new ClassPathXmlApplicationContext(new String[] { "resources/app-context.xml" });

BeanA beanA = applicationContext.getBean(BeanA.class);

BeanB beanB = applicationContext.getBean(BeanB.class);

System.out.println(beanA);

System.out.println(beanB);

}

 

}

 

Output:

BeanB from BeanA

BeanA from BeanB