Spring三级缓存解决循环依赖的解析过程

@Component
public class ServiceA {
    @Autowired
    private ServiceB serviceB;
}

@Component
public class ServiceB {
    @Autowired
    private ServiceA serviceA;
}

// 一级缓存：完整Bean（K:Bean名称 V:实例化+初始化完成的Bean）
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);

// 二级缓存：早期暴露对象（K:Bean名称 V:未完成属性注入的原始Bean）
private final Map<String, Object> earlySingletonObjects = new HashMap<>(16);

// 三级缓存：对象工厂（K:Bean名称 V:ObjectFactory）
private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);

sequenceDiagram
    participant Container
    participant Cache1 as singletonObjects
    participant Cache2 as earlySingletonObjects
    participant Cache3 as singletonFactories
    
    Container->>Cache1: 检查ServiceA是否存在
    Cache1-->>Container: 不存在
    Container->>Container: 实例化ServiceA（构造器调用）
    Container->>Cache3: 添加ServiceA的ObjectFactory
    Container->>Container: 开始属性注入（需要ServiceB）

// AbstractAutowireCapableBeanFactory#doCreateBean
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));

sequenceDiagram
    participant Container
    participant Cache1
    participant Cache2
    participant Cache3
    
    Container->>Cache1: 检查ServiceB是否存在
    Cache1-->>Container: 不存在
    Container->>Container: 实例化ServiceB（构造器调用）
    Container->>Cache3: 添加ServiceB的ObjectFactory
    Container->>Container: 开始属性注入（需要ServiceA）

sequenceDiagram
    participant Container
    participant Cache1
    participant Cache2
    participant Cache3
    
    Container->>Cache1: 查找ServiceA
    Cache1-->>Container: 不存在
    Container->>Cache2: 查找ServiceA
    Cache2-->>Container: 不存在
    Container->>Cache3: 获取ServiceA的ObjectFactory
    Container->>Container: 执行getEarlyBeanReference()
    Container->>Cache2: 将生成的代理对象存入earlySingletonObjects
    Container->>ServiceB: 注入ServiceA的早期引用
    Container->>Container: 完成ServiceB初始化
    Container->>Cache1: 将ServiceB放入singletonObjects

sequenceDiagram
    participant Container
    participant Cache1
    participant Cache2
    participant Cache3
    
    Container->>ServiceA: 注入已初始化的ServiceB
    Container->>Container: 执行ServiceA的初始化后方法
    Container->>Cache1: 将ServiceA放入singletonObjects
    Container->>Cache2: 移除ServiceA的早期引用
    Container->>Cache3: 移除ServiceA的ObjectFactory

protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
    // 如果有必要，在此处生成代理对象
    if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
        for (BeanPostProcessor bp : getBeanPostProcessors()) {
            if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
                SmartInstantiationAwareBeanPostProcessor ibp = 
                    (SmartInstantiationAwareBeanPostProcessor) bp;
                bean = ibp.getEarlyBeanReference(exposedObject, beanName);
            }
        }
    }
    return bean;
}

// 查看三级缓存内容
System.out.println("singletonFactories: " + singletonFactories.keySet());
System.out.println("earlySingletonObjects: " + earlySingletonObjects.keySet());
System.out.println("singletonObjects: " + singletonObjects.keySet());

@Bean
public CircularReferencesBean circularReferencesBean() {
    return new CircularReferencesBean(circularReferencesBean());
}

@Autowired
@Lazy
private ServiceB serviceB;