Spring 循环依赖

缺乏、安全感 2023-07-18 04:47 2阅读 0赞

**目录**

1、概述

2、构造器循环依赖错误示例

创建三个循环依赖类

spring配置

spring引导类

运行结果

分析

3、setter 单例模式下循环依赖示例

循环依赖类

spring配置

引导类

运行结果

分析

4、prototype循环依赖错误示例

上个例子改下spring配置

运行结果

分析

--------------------

# 1、概述 #

循环依赖就是循环引用，例如 A 中有 B，B 中有 A，形成了一个环状引用，这就是循环依赖。

对于构造器循环依赖，无法解决。

setter 循环依赖 在 single （单例）模式下可以解决。

prototype 模式下无法解决。

# 2、构造器循环依赖错误示例 #

## 创建三个循环依赖类 ##

package thinking.in.spring.boot.samples.spring5.circle;
    
    public class CircleA {
    
        private CircleB circleB;
    
        public CircleA(CircleB circleB) {
            this.circleB = circleB;
        }
    
        public CircleB getCircleB() {
            return circleB;
        }
    
        public void setCircleB(CircleB circleB) {
            this.circleB = circleB;
        }
    }

package thinking.in.spring.boot.samples.spring5.circle;
    
    public class CircleB {
    
        private CircleC circleC;
    
        public CircleB(CircleC circleC) {
            this.circleC = circleC;
        }
    
        public CircleC getCircleC() {
            return circleC;
        }
    
        public void setCircleC(CircleC circleC) {
            this.circleC = circleC;
        }
    }

package thinking.in.spring.boot.samples.spring5.circle;
    
    public class CircleC {
    
        private CircleA circleA;
    
        public CircleC(CircleA circleA) {
            this.circleA = circleA;
        }
    
        public CircleA getCircleA() {
            return circleA;
        }
    
        public void setCircleA(CircleA circleA) {
            this.circleA = circleA;
        }
    }

## spring配置 ##

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xmlns:customLabel="http://www.rh.com/schema/customLabel"
           xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans.xsd
            http://www.rh.com/schema/customLabel
            http://www.rh.com/schema/customLabel.xsd">
    
        <bean id="circleA" class="thinking.in.spring.boot.samples.spring5.circle.CircleA">
            <constructor-arg index="0" ref="circleB" />
        </bean>
        <bean id="circleB" class="thinking.in.spring.boot.samples.spring5.circle.CircleB">
            <constructor-arg index="0" ref="circleC" />
        </bean>
        <bean id="circleC" class="thinking.in.spring.boot.samples.spring5.circle.CircleC">
            <constructor-arg index="0" ref="circleA" />
        </bean>
    
    </beans>

## spring引导类 ##

package thinking.in.spring.boot.samples.spring5.bootstrap;
    
    import org.springframework.beans.factory.support.DefaultListableBeanFactory;
    import org.springframework.beans.factory.xml.XmlBeanFactory;
    import org.springframework.core.io.ClassPathResource;
    import thinking.in.spring.boot.samples.spring5.bean.User;
    import thinking.in.spring.boot.samples.spring5.circle.CircleA;
    import thinking.in.spring.boot.samples.spring5.customlabel.CustomLabel;
    import thinking.in.spring.boot.samples.spring5.factorybean.UserFactoryBean;
    
    public class CircleBeanFactoryBootstrap {
    
        public static void main(String[] args) {
            DefaultListableBeanFactory defaultListableBeanFactory = new XmlBeanFactory(new ClassPathResource("application-circle.xml"));
            CircleA circleA = (CircleA) defaultListableBeanFactory.getBean("circleA");
            System.out.println(circleA);
        }
    }

## 运行结果 ##

三月 24, 2020 11:41:40 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
    信息: Loading XML bean definitions from class path resource [application-circle.xml]
    Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'circleA' defined in class path resource [application-circle.xml]: Cannot resolve reference to bean 'circleB' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'circleB' defined in class path resource [application-circle.xml]: Cannot resolve reference to bean 'circleC' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'circleC' defined in class path resource [application-circle.xml]: Cannot resolve reference to bean 'circleA' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'circleA': 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.ConstructorResolver.resolveConstructorArguments(ConstructorResolver.java:622)
    	at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:148)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1274)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1131)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:541)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:501)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
    	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
    	at thinking.in.spring.boot.samples.spring5.bootstrap.CircleBeanFactoryBootstrap.main(CircleBeanFactoryBootstrap.java:15)
    Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'circleB' defined in class path resource [application-circle.xml]: Cannot resolve reference to bean 'circleC' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'circleC' defined in class path resource [application-circle.xml]: Cannot resolve reference to bean 'circleA' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'circleA': 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.ConstructorResolver.resolveConstructorArguments(ConstructorResolver.java:622)
    	at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:148)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1274)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1131)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:541)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:501)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
    	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
    	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)
    	... 12 more
    Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'circleC' defined in class path resource [application-circle.xml]: Cannot resolve reference to bean 'circleA' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'circleA': 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.ConstructorResolver.resolveConstructorArguments(ConstructorResolver.java:622)
    	at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:148)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1274)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1131)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:541)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:501)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
    	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
    	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)
    	... 24 more
    Caused by: org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'circleA': Requested bean is currently in creation: Is there an unresolvable circular reference?
    	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.beforeSingletonCreation(DefaultSingletonBeanRegistry.java:345)
    	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:221)
    	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)
    	... 36 more

## 分析 ##

Spring 正在创建 bean 的时候，都会把正在创建的bean放到一个“当前正在创建 bean 池”中，bean创建过程中一直在这个池子中，直到完成 bean的创建才会从池中删除。

CircleA 正在创建会在池中，因为CircleA引用了 CircleB，所以创建 CircleB，CircleB也进入这个池，CircleB引用了CircleC，CircleC也进入这个池中，CircleC引用了 CircleA，发现CircleA也在池中，并没有创建完毕，这是就会报 BeanCurrentlyInCreationException 异常，告诉你循环依赖异常。

# 3、setter 单例模式下循环依赖示例 #

对构造器依赖循环示例代码进行改造，加无参构造器

## 循环依赖类 ##

package thinking.in.spring.boot.samples.spring5.circle;
    
    public class CircleA {
    
        private CircleB circleB;
    
        public CircleA() {
        }
    
        public CircleA(CircleB circleB) {
            this.circleB = circleB;
        }
    
        public void show() {
            System.out.println("circleA show");
        }
    
        public CircleB getCircleB() {
            return circleB;
        }
    
        public void setCircleB(CircleB circleB) {
            this.circleB = circleB;
        }
    }

package thinking.in.spring.boot.samples.spring5.circle;
    
    public class CircleB {
    
        private CircleC circleC;
    
        public CircleB() {
        }
    
        public CircleB(CircleC circleC) {
            this.circleC = circleC;
        }
    
        public void show() {
            System.out.println("circleB show");
        }
    
        public CircleC getCircleC() {
            return circleC;
        }
    
        public void setCircleC(CircleC circleC) {
            this.circleC = circleC;
        }
    }

package thinking.in.spring.boot.samples.spring5.circle;
    
    public class CircleC {
    
        private CircleA circleA;
    
        public CircleC() {
        }
    
        public CircleC(CircleA circleA) {
            this.circleA = circleA;
        }
    
    
        public void show() {
            System.out.println("circleC show");
        }
    
        public CircleA getCircleA() {
            return circleA;
        }
    
        public void setCircleA(CircleA circleA) {
            this.circleA = circleA;
        }
    }

## spring配置 ##

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xmlns:customLabel="http://www.rh.com/schema/customLabel"
           xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans.xsd
            http://www.rh.com/schema/customLabel
            http://www.rh.com/schema/customLabel.xsd">
    
        <bean id="circleA" class="thinking.in.spring.boot.samples.spring5.circle.CircleA">
            
        </bean>
        <bean id="circleB" class="thinking.in.spring.boot.samples.spring5.circle.CircleB">
            
        </bean>
        <bean id="circleC" class="thinking.in.spring.boot.samples.spring5.circle.CircleC">
            
        </bean>
    
    </beans>

## 引导类 ##

package thinking.in.spring.boot.samples.spring5.bootstrap;
    
    import org.springframework.beans.factory.support.DefaultListableBeanFactory;
    import org.springframework.beans.factory.xml.XmlBeanFactory;
    import org.springframework.core.io.ClassPathResource;
    import thinking.in.spring.boot.samples.spring5.bean.User;
    import thinking.in.spring.boot.samples.spring5.circle.CircleA;
    import thinking.in.spring.boot.samples.spring5.circle.CircleB;
    import thinking.in.spring.boot.samples.spring5.circle.CircleC;
    import thinking.in.spring.boot.samples.spring5.customlabel.CustomLabel;
    import thinking.in.spring.boot.samples.spring5.factorybean.UserFactoryBean;
    
    public class CircleBeanFactoryBootstrap {
    
        public static void main(String[] args) {
            DefaultListableBeanFactory defaultListableBeanFactory = new XmlBeanFactory(new ClassPathResource("application-circle.xml"));
            CircleA circleA = (CircleA) defaultListableBeanFactory.getBean("circleA");
            circleA.show();
            CircleB circleB = (CircleB) defaultListableBeanFactory.getBean("circleB");
            circleB.show();
            CircleC circleC = (CircleC) defaultListableBeanFactory.getBean("circleC");
            circleC.show();
        }
    }

## 运行结果 ##

circleA show
    circleB show
    circleC show

## 分析 ##

因为单例模型 setter 注入方式，首次getBean("circleA")时，Spring容器提前为 CircleA、CircleB、CircleC 各创建一个 ObjectFactory并缓存起来

this.addSingletonFactory(beanName, new ObjectFactory() {
        public Object getObject() throws BeansException {
           return this.getEarlyBeanReference(beanName, mbd, bean);
        }
    });

缓存如下：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3J1YW5oYW8xMjAz_size_16_color_FFFFFF_t_70][]

再次回调getBean("circleA")，调用如下方法

protected Object getSingleton(String beanName, boolean allowEarlyReference) {
            Object singletonObject = this.singletonObjects.get(beanName);
            if (singletonObject == null && this.isSingletonCurrentlyInCreation(beanName)) {
                Map var4 = this.singletonObjects;
                synchronized(this.singletonObjects) {
                    singletonObject = this.earlySingletonObjects.get(beanName);
                    if (singletonObject == null && allowEarlyReference) {
    // 从这里拿出缓存的 ObjectFactory，this.singletonFactories中有CircleA、CircleB、CircleC的 ObjectFactory
                        ObjectFactory<?> singletonFactory = (ObjectFactory)this.singletonFactories.get(beanName);
                        if (singletonFactory != null) {
    // 创建
                            singletonObject = singletonFactory.getObject();
    // 缓存 ObjectFactory.getObject() 创建的bean
                            this.earlySingletonObjects.put(beanName, singletonObject);
    // 移除缓存的 ObjectFactory
                            this.singletonFactories.remove(beanName);
                        }
                    }
                }
            }
    
            return singletonObject;
        }

# 4、prototype循环依赖错误示例 #

## 上个例子改下spring配置 ##

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xmlns:customLabel="http://www.rh.com/schema/customLabel"
           xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans.xsd
            http://www.rh.com/schema/customLabel
            http://www.rh.com/schema/customLabel.xsd">
    
        <bean id="circleA" class="thinking.in.spring.boot.samples.spring5.circle.CircleA" scope="prototype">
            
            <property name="circleB" ref="circleB" />
        </bean>
        <bean id="circleB" class="thinking.in.spring.boot.samples.spring5.circle.CircleB" scope="prototype">
            
            <property name="circleC" ref="circleC" />
        </bean>
        <bean id="circleC" class="thinking.in.spring.boot.samples.spring5.circle.CircleC" scope="prototype">
            
            <property name="circleA" ref="circleA" />
        </bean>
    
    </beans>

## 运行结果 ##

"D:\Program Files\Java\jdk1.8.0_201\bin\java" "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA 2017.2.7\lib\idea_rt.jar=58065:D:\Program Files\JetBrains\IntelliJ IDEA 2017.2.7\bin" -Dfile.encoding=UTF-8 -classpath "D:\Program Files\Java\jdk1.8.0_201\jre\lib\charsets.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\deploy.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\access-bridge-64.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\cldrdata.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\dnsns.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\jaccess.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\jfxrt.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\localedata.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\nashorn.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunec.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunjce_provider.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunmscapi.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunpkcs11.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\zipfs.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\javaws.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\jce.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\jfr.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\jfxswt.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\jsse.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\management-agent.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\plugin.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\resources.jar;D:\Program Files\Java\jdk1.8.0_201\jre\lib\rt.jar;F:\github_workspace\thinking-in-spring-boot-samples\spring-framework-samples\spring-framework-5.0.x-sample-rh\target\classes;E:\maven\ali_repo\org\springframework\spring-context\5.0.6.RELEASE\spring-context-5.0.6.RELEASE.jar;E:\maven\ali_repo\org\springframework\spring-aop\5.0.6.RELEASE\spring-aop-5.0.6.RELEASE.jar;E:\maven\ali_repo\org\springframework\spring-beans\5.0.6.RELEASE\spring-beans-5.0.6.RELEASE.jar;E:\maven\ali_repo\org\springframework\spring-core\5.0.6.RELEASE\spring-core-5.0.6.RELEASE.jar;E:\maven\ali_repo\org\springframework\spring-jcl\5.0.6.RELEASE\spring-jcl-5.0.6.RELEASE.jar;E:\maven\ali_repo\org\springframework\spring-expression\5.0.6.RELEASE\spring-expression-5.0.6.RELEASE.jar;E:\maven\ali_repo\org\springframework\spring-tx\5.0.6.RELEASE\spring-tx-5.0.6.RELEASE.jar;E:\maven\ali_repo\org\springframework\spring-context-indexer\5.0.6.RELEASE\spring-context-indexer-5.0.6.RELEASE.jar" thinking.in.spring.boot.samples.spring5.bootstrap.CircleBeanFactoryBootstrap
    三月 24, 2020 3:02:43 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
    信息: Loading XML bean definitions from class path resource [application-circle.xml]
    Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'circleA' defined in class path resource [application-circle.xml]: Cannot resolve reference to bean 'circleB' while setting bean property 'circleB'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'circleB' defined in class path resource [application-circle.xml]: Cannot resolve reference to bean 'circleC' while setting bean property 'circleC'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'circleC' defined in class path resource [application-circle.xml]: Cannot resolve reference to bean 'circleA' while setting bean property 'circleA'; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'circleA': 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:1609)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1361)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:578)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:501)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:335)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
    	at thinking.in.spring.boot.samples.spring5.bootstrap.CircleBeanFactoryBootstrap.main(CircleBeanFactoryBootstrap.java:17)
    Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'circleB' defined in class path resource [application-circle.xml]: Cannot resolve reference to bean 'circleC' while setting bean property 'circleC'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'circleC' defined in class path resource [application-circle.xml]: Cannot resolve reference to bean 'circleA' while setting bean property 'circleA'; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'circleA': 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:1609)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1361)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:578)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:501)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:335)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
    	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:367)
    	... 8 more
    Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'circleC' defined in class path resource [application-circle.xml]: Cannot resolve reference to bean 'circleA' while setting bean property 'circleA'; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'circleA': 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:1609)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1361)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:578)
    	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:501)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:335)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
    	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:367)
    	... 16 more
    Caused by: org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'circleA': Requested bean is currently in creation: Is there an unresolvable circular reference?
    	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:264)
    	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
    	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:367)
    	... 24 more
    
    Process finished with exit code 1

## 分析 ##

prototype 作用域因为无法提前暴露一个创建中的bean（ObjectFactory），所以会报异常。

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