Spring 循环依赖，即使使用通过 setter 注入

Question

我对 Spring 循环依赖项有一个我不理解的特定问题。我已经编译了一个简单的示例来重现该问题并类似于我的大型应用程序：

@Configuration
@ImportResource("classpath:my-spring-config.xml")
public class DeleteMeSpringTest {

    @Test
    public void test() {
        AnnotationConfigApplicationContext appContext = new AnnotationConfigApplicationContext("extremeSpecial");
        appContext.register(DeleteMeSpringTest.class);

        MainUIFrame master = appContext.getBean(MainUIFrame.class);
        System.out.println(master.toString());
    }

    public static class DialogProvider {
        private JComponent component;

        public void setComponent(final JComponent master) {
            this.component = master;
        }
    }

    @Component(value = "nestedUIComponent")
    public static class SomeNestedUIView extends JComponent {
        private DialogProvider dialogProvider;

        @Autowired
        public void setDialogProvider(final @Qualifier("nestedDialogProvider") DialogProvider dialogProvider) {
            this.dialogProvider = dialogProvider;
        }
    }

    @Component(value = "mainUIFrame")
    public static class MainUIFrame extends JComponent {
        private final SomeNestedUIView compA;
        private final DialogProvider mainDialogProvider;

        public MainUIFrame(final SomeNestedUIView compA, final @Qualifier("mainDialogProvider") DialogProvider dialogProvider) {
            this.compA = compA;
            this.mainDialogProvider = dialogProvider;
        }
    }

}

以下 XML bean 定义也存在：

<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns="http://www.springframework.org/schema/beans"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean class="extremeSpecial.DeleteMeSpringTest$DialogProvider" id="mainDialogProvider">
        <property name="component" ref="mainUIFrame"/>
    </bean>

    <bean class="extremeSpecial.DeleteMeSpringTest$DialogProvider" id="nestedDialogProvider">
        <property name="component" ref="nestedUIComponent"/>
    </bean>
</beans>

查看代码应该实现以下循环结构：mainDialogProvider -> MainUIFrame -> mainDialogProvider。但是我不明白为什么 Spring 无法解决循环依赖：

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'mainUIFrame': Unsatisfied dependency expressed through constructor parameter 1; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mainDialogProvider' defined in class path resource [my-spring-config.xml]: Cannot resolve reference to bean 'mainUIFrame' while setting bean property 'component'; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'mainUIFrame': Requested bean is currently in creation: Is there an unresolvable circular reference?

at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:732)
at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:197)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1267)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1124)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:535)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:759)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:869)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550)
at org.springframework.context.annotation.AnnotationConfigApplicationContext.<init>(AnnotationConfigApplicationContext.java:99)
at extremeSpecial.DeleteMeSpringTest.test(DeleteMeSpringTest.java:25)
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mainDialogProvider' defined in class path resource [my-spring-config.xml]: Cannot resolve reference to bean 'mainUIFrame' while setting bean property 'component'; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'mainUIFrame': Requested bean is currently in creation: Is there an unresolvable circular reference?
at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:378)
at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:110)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1602)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1354)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:572)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:251)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1135)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1062)
at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:818)
at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:724)
... 36 more
Caused by: org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'mainUIFrame': Requested bean is currently in creation: Is there an unresolvable circular reference?
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.beforeSingletonCreation(DefaultSingletonBeanRegistry.java:339)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:215)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:367)
... 50 more

我原以为通过使用 setter 注入（或 XML 中的属性），Spring 应该能够首先在没有属性的情况下创建 bean，然后再使用 setter 注入循环依赖项。对于更简单的示例（例如，此处演示：https://stackoverflow.com/a/49188520/606513），它的工作原理正是如此，但是我的示例中的某些东西会导致它中断，我需要找出那是什么！

请注意，通过避免使用 XML 文件（并且不需要两个不同的 DialogProvider 实例），Spring 可以毫无问题地解决主循环！

Answer 1

我在最新的 Spring Boot 中测试了您的代码，它工作正常，我所做的唯一更改是用 @Bean 替换 xml 配置并移动设置器，xml-beans 是有效的构造函数自动装配，因此导致了问题：

 @Bean
    public MainFrameDialogProvider mainDialogProvider(MainUIFrame master) {
        return new MainFrameDialogProvider(master, "mainDialogProvider");
    }

    @Bean
    public MainFrameDialogProvider nestedDialogProvider(SomeNestedUIView master) {
        return new MainFrameDialogProvider(master, "nestedDialogProvider");
    }

    public static class MainFrameDialogProvider {
        private final Object master;
        private final String nestedDialogProvider;

        public MainFrameDialogProvider(Object master, String nestedDialogProvider) {
            this.master = master;
            this.nestedDialogProvider = nestedDialogProvider;
        }
    }

    @Component
    public static class SomeNestedUIView {
        private MainFrameDialogProvider dialogProvider;

        @Autowired
        public void setMainFrameDialogProvider(@Qualifier("nestedDialogProvider") MainFrameDialogProvider dialogProvider) {
            this.dialogProvider = dialogProvider;
        }
    }

    @Component
    public static class MainUIFrame {
        private SomeNestedUIView compA;
        private MainFrameDialogProvider mainFrameDialogProvider;

        @Autowired
        public void setCompA(SomeNestedUIView compA) {
            this.compA = compA;
        }

        @Autowired
        public void setMainFrameDialogProvider(@Qualifier("mainDialogProvider") MainFrameDialogProvider mainFrameDialogProvider) {
            this.mainFrameDialogProvider = mainFrameDialogProvider;
        }
    }
}

使用 spring-boot 2.1.7

编辑：我的解决方案并没有忽略有两个不同实例的事实：