就是A对象依赖了B对象,B对象依赖了A对象,构成了一个环
// A依赖了B
class A {
public B b;
}
// B依赖了A
class B{
public A a;
}
SingletonBeanRegistry
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);
二级缓存(未初始化未填充属性提前暴露的Bean)
private final Map<String, Object> earlySingletonObjects = new HashMap<>(16);
三级缓存(Bean创建时提供代理机会的Bean工厂缓存)
private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);