How to Handle Circular Dependencies in Spring or Other Dependency Injection Frameworks

Circular dependencies occur in dependency injection frameworks like Spring when two or more beans depend on each other, creating a cycle that prevents proper initialization. For instance, if Bean A depends on Bean B, and Bean B depends on Bean A, this creates a circular dependency.

1. Use @Lazy Annotation

Spring provides the @Lazy annotation, which delays the initialization of a bean until it’s required. Applying this annotation to one of the beans in the cycle breaks the immediate dependency chain.

@Component
public class BeanA {

    private final BeanB beanB;

    public BeanA(@Lazy BeanB beanB) {
        this.beanB = beanB;
    }

    public void doSomething() {
        System.out.println("BeanA is working with BeanB");
        beanB.doSomething();
    }
}

@Component
public class BeanB {

    private final BeanA beanA;

    public BeanB(BeanA beanA) {
        this.beanA = beanA;
    }

    public void doSomething() {
        System.out.println("BeanB is working with BeanA");
    }
}

Here, the @Lazy annotation ensures that BeanB is initialized only when needed, preventing the circular dependency from causing a failure.

2. Refactor Dependencies

Refactoring dependencies is one of the best ways to handle circular dependencies in Spring. This involves restructuring your code to eliminate the direct cycle, often by introducing a third intermediary bean or service.

@Component
public class BeanA {

    private final CommonService commonService;

    public BeanA(CommonService commonService) {
        this.commonService = commonService;
    }

    public void execute() {
        commonService.performTask();
    }
}

@Component
public class BeanB {

    private final CommonService commonService;

    public BeanB(CommonService commonService) {
        this.commonService = commonService;
    }

    public void execute() {
        commonService.performTask();
    }
}

@Component
public class CommonService {

    public void performTask() {
        System.out.println("Performing a common task.");
    }
}

3. Use @PostConstruct and @Autowired

Another approach involves using @Autowired and @PostConstruct to defer the dependency resolution until after bean initialization.

@Component
public class BeanA {

    private BeanB beanB;

    @Autowired
    public void setBeanB(BeanB beanB) {
        this.beanB = beanB;
    }

    @PostConstruct
    public void init() {
        System.out.println("BeanA initialized and ready to use BeanB");
    }
}

@Component
public class BeanB {

    private final BeanA beanA;

    public BeanB(BeanA beanA) {
        this.beanA = beanA;
    }
}

4. Change Constructor Injection to Setter Injection

@Component
public class BeanA {

    private BeanB beanB;

    @Autowired
    public void setBeanB(BeanB beanB) {
        this.beanB = beanB;
    }

    public void doSomething() {
        beanB.doSomething();
    }
}

@Component
public class BeanB {

    private BeanA beanA;

    @Autowired
    public void setBeanA(BeanA beanA) {
        this.beanA = beanA;
    }

    public void doSomething() {
        System.out.println("BeanB is working with BeanA");
    }
}

Setter injection gives Spring more flexibility in resolving circular dependencies.

5. Use ApplicationContextAware

For advanced scenarios, implementing the ApplicationContextAware interface allows you to programmatically fetch dependencies.

@Component
public class BeanA {

    private BeanB beanB;

    @Autowired
    private ApplicationContext applicationContext;

    @PostConstruct
    public void init() {
        this.beanB = applicationContext.getBean(BeanB.class);
    }

    public void doSomething() {
        beanB.doSomething();
    }
}

@Component
public class BeanB {

    public void doSomething() {
        System.out.println("BeanB is working independently");
    }
}

This method avoids cycles by programmatically retrieving dependencies.

Circular dependencies can be challenging but are manageable with the right techniques. Whether you use lazy initialization, refactor dependencies, or employ setter injection, the key is to design your beans to minimize coupling. These approaches provide a robust way to handle circular dependencies in Spring, helping you create a cleaner and more maintainable application.

1. Use @Lazy Annotation

2. Refactor Dependencies

3. Use @PostConstruct and @Autowired

4. Change Constructor Injection to Setter Injection

5. Use ApplicationContextAware

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