Spring 引导中基于字段和基于构造函数的循环依赖

Question

@Component 
public class RandomA {
    
    @Autowired
    public RandomB randB;
    
    public RandomA()
    {
        System.out.println("Bello");
    }
    
    public void get()
    {
        System.out.println("AAA");
    }
    

}

@Component
public class RandomB {
    
    public RandomB()
    {
        System.out.println("Hello");
    }
    
     @Autowired
    public RandomA randA;
     
     public void get()
        {
            System.out.println("BBB");
        }
}

I was expecting the above code to give a circular dependency error in spring boot but it executes fine without any error.

On the other side:

@Component  
public class RandomA {
    
    public RandomB randB;
    
    public RandomA(RandomB randB)
    {
        this.randB=randB;
        System.out.println("Bello");
    }
    
    
    public void get()
    {
        System.out.println("AAA");
    }
}

@Component
public class RandomB {
    
    @Autowired
    public RandomB(RandomA randA)
    {
        this.randA=randA;
        System.out.println("Hello");
    }
    
    public RandomA randA;
    
     public void get()
        {
            System.out.println("BBB");
        }
}

This code leads to circular dependency error.

Can anyone explain why the 1st one don't lead to circular dependency?/

Thank you.

Answer 1

In the second example you have the constructor injection, so in case of circular dependency it should fail. In the first example you use autowiring so dependencies will be injected when they are needed and not on the context loading.

More details here: https://www.baeldung.com/circular-dependencies-in-spring