spring解决循环依赖

Posted 2022-04-29 lxk2010012997

之前面试有被问到过，面试官很调皮，我擅长的点没有问，然后抽了一个点让我回答，这个点考察了源码的理解，当时只是大概记得是提前暴露，但是细节答得有些粗糙，特补充一下，，，

	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 != NULL_OBJECT ? singletonObject : null);
	

　　解决循环依赖的核心代码如上，首先会从singletonObjects缓存中取对象，如果对象不存在，但处于创建中，则加锁缓存，然后从提前暴露单例缓存中去拿对象，仍然无法取到则查看是否允许提前引用，如果允许，则从单例工厂缓存中获取单例工厂，然后从工厂中获取单例对象，然后将单例工厂从工厂缓存中移除。