二、spring源码之循环依赖的主要方法

主要依靠下面几个方法：

1、getSingleton从缓存中获取单例对象

（

getBean->doGetBean方法中会调用该方法。

这里简单解释了doGetBean方法的大致流程：https://blog.csdn.net/qq_36951116/article/details/100031182

）

并且第二个参数为true，表示这个bean运行早期被引用。作用通过下面的代码可以看到，就当为true时，如果bean被提前暴露在了singletonFactories中，那么就会被获取出来，然后添加到earlySingletonObjects中。

protected Object getSingleton(String beanName, boolean allowEarlyReference) {
		Object singletonObject = this.singletonObjects.get(beanName);
		if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
			synchronized (this.singletonObjects) {
				singletonObject = this.earlySingletonObjects.get(beanName);
				if (singletonObject == null && allowEarlyReference) {
					ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
					if (singletonFactory != null) {
						singletonObject = singletonFactory.getObject();
						this.earlySingletonObjects.put(beanName, singletonObject);
						this.singletonFactories.remove(beanName);
					}
				}
			}
		}
		return singletonObject;
	}
           

2、addSingletonFactory添加对象工厂ObjectFactory

（添加的对象工厂都是用于获取提前暴露出来的bean的，该方法只在一个地方被调用，在doCreateBean方法中，bean刚被创建出来，还没有被注入属性、没有被后置处理器处理时，bean会被方法对象工厂中，然后再把对象工厂通过该方法添加到singletonFactories中）

protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
		Assert.notNull(singletonFactory, "Singleton factory must not be null");
		synchronized (this.singletonObjects) {
			if (!this.singletonObjects.containsKey(beanName)) {
				this.singletonFactories.put(beanName, singletonFactory);
				this.earlySingletonObjects.remove(beanName);
				this.registeredSingletons.add(beanName);
			}
		}
	}
           

3、addSingleton添加最终版的bean到singletonObjects

protected void addSingleton(String beanName, Object singletonObject) {
		synchronized (this.singletonObjects) {
			this.singletonObjects.put(beanName, singletonObject);
			this.singletonFactories.remove(beanName);
			this.earlySingletonObjects.remove(beanName);
			this.registeredSingletons.add(beanName);
		}
	}