java - org.springframework.beans.factory.BeanCurrentlyInCreationException : Spring cyclic dependency - constructor Autowiring

Question

旧代码:

@Component("someFactory")
public class SomeFactoryImpl implements SomeFactory{

    @Autowired
    private List<SomeTransformer<?, ?>> someTransformers;

新代码:

@Component("someFactory")
public class SomeFactoryImpl implements SomeFactory {

    private List<SomeTransformer<?, ?>> someTransformers;

    @Autowired
    public SomeFactoryImpl(List<SomeTransformer<?, ?>> someTransformers) {
        this.someTransformers = someTransformers;
     }

我得到了:

org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'someFactory': Requested bean is currently in creation: Is there an unresolvable circular reference?

Spring 在通过构造函数 Autowiring 时是否有一些问题？

Answer 1

检查 Spring documentation (查找“循环依赖项”)。

Unlike the typical case (with no circular dependencies), a circular dependency between bean A and bean B forces one of the beans to be injected into the other prior to being fully initialized itself (a classic chicken/egg scenario).

区别在于:

在Setter 注入(inject) 中，bean 引用只会在需要时才构建。当使用 @Required 注释 setter 时，您可能会重新创建与 setter 注入(inject)相同的问题，因为这将导致立即创建 bean。

在构造函数注入(inject)中，Spring 无法决定首先创建哪个 bean，因为它们相互依赖。问题立即暴露。一种可能的解决方法是使用带有 @Lazy 注释的构造函数注入(inject)；

@Component
public class CircularClassA {

    private CircularClassB classB;

    @Autowired
    public CircularDependencyB(@Lazy CircularClassB classB) {
        this.classB = classB;
    }
}

这将只创建 classB 的代理，而不是完全初始化它。它会在需要时完全初始化，就像 setter 注入(inject)一样。