Spring如何使用三级缓存解决循环依赖

public class PersonA { 
  @Autowired
  private PersonB personB;
}

public class PersonB {
  @Autowired
  private PersonA personA;
}

/** 一级缓存 */
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>(256);
/** 二级缓存 */ 
private final Map<String, Object> earlySingletonObjects = new HashMap<String, Object>(16); 
/** 三级缓存 */ 
private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<String, ObjectFactory<?>>(16);

protected <T> T doGetBean( String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly) throws BeansException {
  // 获取bean的规范名称
  String beanName = transformedBeanName(name); 
  Object bean;  
  // 从各级缓存中获取bean对象 
  Object sharedInstance = getSingleton(beanName); 
  // 跟factoryBean相关判断
  if (sharedInstance != null && args == null) { 
...
  } 
  // 获取factorybean的真是bean
  //若为普通bean则直接返回对象

  bean = getObjectForBeanInstance(sharedInstance, name, beanName, null); 
} 
...... 
  // 创建单利bean对象 
  if (mbd.isSingleton()) { 
    sharedInstance = getSingleton(beanName, () -> { 
  try {
    // 创建bean
    return createBean(beanName, mbd, args); 
  } catch (BeansException ex) { 
    // Explicitly remove instance from singleton cache: It might have been put there 
    // eagerly by the creation process, to allow for circular reference resolution. 
    // Also remove any beans that received a temporary reference to the bean. destroySingleton(beanName); 
    throw ex; 
  } 
}); 
  bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd); 
} 
......    
// 返回bean对象 return (T) bean; }

// 这个方法主要是三级缓存容器，思路大概是：从一级缓存查询，若找不到去二级缓存查询，还是不存在则去三级缓存，若三级缓存找到了，则将bean放入二级缓存中
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
  // 从一级缓存中查找bean
  Object singletonObject = this.singletonObjects.get(beanName);
  // 判断一级缓存查找不到bean && bean是否处于创建中，成立，则进入循环依赖
  if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
    synchronized (this.singletonObjects) {
    // 从二级缓存中查找
    singletonObject = this.earlySingletonObjects.get(beanName);
    // 二级缓存未查询到 && 是否允许获取早期引用
    if (singletonObject == null && allowEarlyReference) {
      // 从三级缓存查询
      ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
      // 三级缓存存在bean
      if (singletonFactory != null) {
        // 获取bean实例
        singletonObject = singletonFactory.getObject();
        // 从三级缓存升级到二级缓存，
        this.earlySingletonObjects.put(beanName, singletonObject);
        // 三级缓存中移除
        this.singletonFactories.remove(beanName);
        }
      }
    }
  }
   // 返回bean
  return singletonObject;
}

public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {  
  Assert.notNull(beanName, "Bean name must not be null");  
  synchronized (this.singletonObjects) {        
  // 从一级缓存中获取对应bean 
  Object singletonObject = this.singletonObjects.get(beanName);      
  // 若bean不存在 
  if (singletonObject == null) {  
    // 当前正在销毁bean，不能创建
    if (this.singletonsCurrentlyInDestruction) {  
      throw new BeanCreationNotAllowedException(beanName, "Singleton bean creation not allowed while singletons of this factory are in destruction " + "(Do not request a bean from a BeanFactory in a destroy method implementation!)");  
    }  
    if (logger.isDebugEnabled()) {  
      logger.debug("Creating shared instance of singleton bean '" + beanName + "'");  
    }
    // 创建前检查，记录正在加载状态     
    beforeSingletonCreation(beanName); 
    boolean newSingleton = false;
    boolean recordSuppressedExceptions = (this.suppressedExceptions == null);  
    // 如果当前没有异常，初始化异常集合
    if (recordSuppressedExceptions) {  
      this.suppressedExceptions = new LinkedHashSet<>();  
    }  
    try {
      // 执行匿名内部类方法 
      singletonObject = singletonFactory.getObject(); 
      newSingleton = true; 
    }  
    catch(IllegalStateException ex){  
      // 执行getObject方法创建bean
      singletonObject = this.singletonObjects.get(beanName);  
      if (singletonObject == null) {  
        throw ex;  
      }  
    } catch(BeanCreationException ex){  
      if (recordSuppressedExceptions) {  
        or (Exception suppressedException : this.suppressedExceptions) { 
          ex.addRelatedCause(suppressedException);  
      }  
    }  
      throw ex;  
    } finally{  
      if (recordSuppressedExceptions) {  
        this.suppressedExceptions = null;  
      } 
      // 单例bean创建完成后，容器移除bean
      afterSingletonCreation(beanName);  
    }  
    // newSingleton为true时，表示bean创建成功  
    // 判断是否为新的完成整bean
    if (newSingleton) {            
      // 将bean存入一级缓存中
      addSingleton(beanName, singletonObject);  
    }  
   } 
   return singletonObject;  
  }  
}

// 将bean放入一级缓存切清楚二级、三级缓存
protected void addSingleton(String beanName, Object singletonObject) {
  synchronized (this.singletonObjects) {xw
    // 添加到一级缓存中 
    this.singletonObjects.put(beanName, singletonObject); 
    // 从三级缓存中移除 
    this.singletonFactories.remove(beanName);
    // 从二级缓存中移除 
    this.earlySingletonObjects.remove(beanName);
    // 放入已注册的单利池中
    this.registeredSingletons.add(beanName);
  }
}

// 添加到三级缓存
protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
  synchronized (this.singletonObjects) {
  // 若一级缓存不存在bean实例
  if (!this.singletonObjects.containsKey(beanName)) {
    // 添加到三级缓存
    this.singletonFactories.put(beanName, singletonFactory);
    // 从第二级缓存删除
    this.earlySingletonObjects.remove(beanName);
    // 放入已注册的单例池里
    this.registeredSingletons.add(beanName);
  }
}