简介
package org.springframework.beans.factory.support;
public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements SingletonBeanRegistry {
/** Cache of singleton objects: bean name to bean instance. */
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);
/** Cache of singleton factories: bean name to ObjectFactory. */
private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);
/** Cache of early singleton objects: bean name to bean instance. */
private final Map<String, Object> earlySingletonObjects = new ConcurrentHashMap<>(16);
}
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singletonObjects：一级缓存，调用 getBean() 可以直接获取初始化完成的 单例对象。
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earlySingletonObjects：二级缓存，已经被 AOP 增强，但是还有属性没有注入完。
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singletonFactories：遍历所有的 BeanPostProcessor 后置处理器，通过 SmartInstantiationAwareBeanPostProcessor 类型的后置处理器进行 AOP 增强。
缓存初始化时机
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singletonFactories：实例化对象（createBeanInstance 方法）之后，填充属性（populateBean 方法）之前。
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
// 1. 实例化 Bean 对象
BeanWrapper instanceWrapper = createBeanInstance(beanName, mbd, args);
// 2. 把用 lambda 表达式 表示的 ObjectFactory，添加到 singletonFactories 缓存
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
// Initialize the bean instance.
Object exposedObject = bean;
try {
// 3. 填充 Bean 对象的属性
populateBean(beanName, mbd, instanceWrapper);
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
return exposedObject;
}
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earlySingletonObjects：存在循环引用时才会初始化。在 getSingleton() 方法中，通过 singletonFactories 获取到 AOP 对象后填入。
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) {
// 1. 获取到 ObjectFactory 缓存
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {
// 2. 通过 `getEarlyBeanReference()` 方法得到 AOP 增强的代理对象
singletonObject = singletonFactory.getObject();
// 3. 将 AOP 增强的代码对象存放到 earlySingletonObjects 缓存中
this.earlySingletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
}
}
}
}
return singletonObject;
}
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singletonObjects：单例对象 初始化完成（属性填充完毕，以及执行完所有的 Spring 初始化生命周期方法后）填入。
参考
