要弄清楚循环依赖
1,需要知道Bean初始化的两个阶段
①豆实例化创建实例对象(新Bean ())
②豆实例对象初始化(DI:注解自动注入)
2, DefaultSingletonBeanRegistry类中的5个容器
/* *记录已将创建的单例& lt; beanName, singletonBean>＊／
私人最终Map<字符串,Object>singletonObjects=new ConcurrentHashMap<祝辞(256);/* *记录singletonFactorysingeletonFactory中存放beanName和上面的①阶段的bean:豆实例化实例对象(还未初始化DI) */私人最终Map<字符串,ObjectFactory<& # 63;在祝辞singletonFactories=new HashMap<祝辞(16);/* *记录早期的singletonBean存放的也是①*/私人最终Map<字符串,Object>earlySingletonObjects=new HashMap<祝辞(16);/* *存放已经初始化后的beanName,有序*/私人最终SetregisteredSingletons=new LinkedHashSet<祝辞(256);/* *记录正在初始化的bean的beanName */私人最终SetsingletonsCurrentlyInCreation=集合。newSetFromMap(新ConcurrentHashMap<祝辞(16));
其中跟循环依赖相关的是singletonFactories, singeletonsCurrentlyInCreation earlysingletonObjects。
3,循环依赖实现
①bean初始化前后会打标,加入到singletonsCurrentlyInCreation容器中,这个打标会在核心方法getSingleton()中起作用
/* org.springframework.beans.factory.support.DefaultSingletonBeanRegistry # getSingleton (. lang。字符串,org.springframework.beans.factory.ObjectFactory<& # 63;祝辞)*/公共对象getSingleton(字符串beanName ObjectFactory<& # 63;比;singletonFactory) {
…//循环依赖相关:初始化前先singletonsCurrentlyInCreation.add (beanName)
beforeSingletonCreation (beanName);
…//λ表达式:其实是调用createBean (mbd beanName, args):豆初始化
singletonObject=singletonFactory.getObject ();
…//循环依赖相关:初始化后singletonsCurrentlyInCreation.remove (beanName)
afterSingletonCreation (beanName);
…//初始化完后//this.singletonObjects。把(beanName singletonObject);放入到单例容器中//this.singletonFactories.remove (beanName);清空循环依赖的两个打标//this.earlySingletonObjects.remove (beanName);//this.registeredSingletons.add (beanName);放入单例beanName容器中
addSingleton (beanName singletonObject);
…
}
}
②上面singletonObject=singletonFactory.getObject()时向singletonFactories中记录了(新Bean ()), singletonFactories也会在核心方法getSingleton()中起作用
/* org.springframework.beans.factory.support。AbstractAutowireCapableBeanFactory # doCreateBean */保护对象doCreateBean(最终字符串beanName,最后RootBeanDefinition mbd,最后@Nullable Object[]参数)
抛出BeanCreationException {
…//循环依赖相关逻辑://this.singletonFactories。把(beanName singletonFactory);//将实例化bean(①阶段),beanName组装成singletonFactory装入singletonFactories容器//this.earlySingletonObjects.remove (beanName);//删除earlySingletonObjects中beanName
addSingletonFactory (beanName ()→getEarlyBeanReference (beanName mbd bean));
…//实例初始化就是在这里面实现依赖注入DI的:反射实现//调用AutowiredAnnotationBeanPostProcessor.postProcessProperties
populateBean (beanName mbd instanceWrapper);
…
}
③核心方法getSingleton
/* org.springframework.beans.factory.support.DefaultSingletonBeanRegistry # getSingleton (. lang。字符串、布尔值)*/保护对象getSingleton(字符串beanName,布尔allowEarlyReference) {
对象singletonObject=this.singletonObjects.get (beanName);//循环依赖核心就在于这个判断,由于打标+记录了①阶段的bean//循环依赖第二次调用getBean (“a”)时,这里会直接返回第一次调用getBean (“a”)创建的①阶段的bean//而不会调用createBean (“a”)再次豆初始化(造成两个bean的循环创建)
如果(singletonObject==零,,isSingletonCurrentlyInCreation (beanName)) {
同步(this.singletonObjects) {
singletonObject=this.earlySingletonObjects.get (beanName);
如果(singletonObject==零,,allowEarlyReference) {
ObjectFactory<& # 63;比;singletonFactory=this.singletonFactories.get (beanName);
如果(singletonFactory !=null) {
singletonObject=singletonFactory.getObject ();
this.earlySingletonObjects。把(beanName singletonObject);
this.singletonFactories.remove (beanName);
}
}
}
}
返回singletonObject;
}
④循环依赖流程
