为了避免循环依赖，我可以在setter上使用@Autowired而不是构造器。
如果是这样，为什么会失败？
@Component
private static class A {
@Autowired
public A(B b) {
}
}
@Component
private static class B {
private A a;
public B() {
}
@Autowired
public void setA(A a) {
this.a = a;
}
}字符串
如果我像B一样定义A类，一切都没问题，但是上面的一个应该已经工作了，为什么它不工作？我在A类的构造函数中无法摆脱依赖关系。在这种情况下我该怎么办？
编辑：我正在使用Spring 3.2.1.RELEASE
编辑2：我的例外：
Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'dependencyTest.A' defined in file [/home/adam/workspaces/testproject/target/classes/mypackage/test/DependencyTest$A.class]: Unsatisfied dependency expressed through constructor argument with index 0 of type [mypackage.test.DependencyTest$B]: : Error creating bean with name 'dependencyTest.B': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire method: public void mypackage.test.DependencyTest$B.setA(mypackage.test.DependencyTest$A); nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'dependencyTest.A': Requested bean is currently in creation: Is there an unresolvable circular reference?; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dependencyTest.B': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire method: public void mypackage.test.DependencyTest$B.setA(mypackage.test.DependencyTest$A); nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'dependencyTest.A': Requested bean is currently in creation: Is there an unresolvable circular reference?
at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:730)
at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:196)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1049)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:953)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:490)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:461)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:295)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:223)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:292)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:626)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:932)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:479)
at org.springframework.context.annotation.AnnotationConfigApplicationContext.<init>(AnnotationConfigApplicationContext.java:84)
at mypackage.test.DependencyTest.main(DependencyTest.java:10)
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dependencyTest.B': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire method: public void mypackage.test.DependencyTest$B.setA(mypackage.test.DependencyTest$A); nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'dependencyTest.A': Requested bean is currently in creation: Is there an unresolvable circular reference?
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:288)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1120)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:522)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:461)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:295)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:223)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:292)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:891)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:834)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:749)
at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:795)
at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:723)
... 14 more
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire method: public void mypackage.test.DependencyTest$B.setA(mypackage.test.DependencyTest$A); nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'dependencyTest.A': Requested bean is currently in creation: Is there an unresolvable circular reference?
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.inject(AutowiredAnnotationBeanPostProcessor.java:601)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:87)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:285)
... 26 more
Caused by: org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'dependencyTest.A': Requested bean is currently in creation: Is there an unresolvable circular reference?
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.beforeSingletonCreation(DefaultSingletonBeanRegistry.java:327)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:217)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:292)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:891)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:834)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:749)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.inject(AutowiredAnnotationBeanPostProcessor.java:558)
... 28 more型
2条答案
按热度按时间pgvzfuti1#
我认为Spring还不够聪明，没有意识到这种关系必须以特定的顺序加载，以避免看起来像一个无法解析的循环引用。它通常通过在构造它们之后但在完全填充它们之前缓存单例示例来处理循环引用，这样它就可以在需要的地方注入示例，即使它还没有填充，因为它知道它稍后会完成设置。
实际情况是，它试图先创建A，但它甚至不能在没有B的情况下构建一个，所以它不能缓存A示例。然后它试图创建B，发现它需要A，但它知道它正在创建A，但没有缓存的示例用于依赖项，所以它失败了。你需要强制它先用类似
@DependsOn("dependencyTest.B")的东西创建B示例。然后可以进行单例缓存，因为B可以在不需要A的情况下构造，所以在创建A时，未填充的B示例将可用。gev0vcfq2#
bean首先被示例化，然后相互注入。这就是为什么你会面临这种情况。当
A被示例化时，它需要B。使用setter而不是constructor可以解决这个问题，因为示例化阶段是在不添加依赖项的情况下完成的。