BeanFactory getBean 流程：getBean -> doGetBean -> getSingleton -> singletonFactory.getObject() -> createBean ->doCreateBean->initializeBean

1. getSingleton

從緩存中獲取已經(jīng)創(chuàng)建的單例bean暂吉，或者是返回一個 early reference匾灶，從而新創(chuàng)建一個bean

    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);
    }

2. doGetBean

不同的scope生成bean的策略不同

protected <T> T doGetBean(){
    // 查看是否緩存在  singletonObjects 中
    Object sharedInstance = getSingleton(beanName);
    //如果不為空，則直接返回緩存中
    if (sharedInstance != null && args == null) {
        bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
    }else {
        //如果未能在緩存中找到bean蒙挑，需要根據(jù)bean的scope新建一個bean
        if (mbd.isSingleton()) {
            sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
                 @Override
                  public Object getObject() throws BeansException {
                        return createBean(beanName, mbd, args);
                   }
             bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
        }else if (mbd.isPrototype()) {
             Object prototypeInstance = null;
             try {
                beforePrototypeCreation(beanName);
                prototypeInstance = createBean(beanName, mbd, args);
              }finally {
                  afterPrototypeCreation(beanName);
              }
              bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd); } 
          else {
              createBean(beanName, mbd, args);
              ...
        }
    }
}

3. createBean

給BeanPostProcessor一個創(chuàng)建并返回代理bean的機(jī)會

protected Object createBean(){      
    // 生成BeanPostProcessor的代理類
    Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
    if (bean != null) {
      return bean;
    }
    ...
    Object beanInstance = doCreateBean(beanName, mbdToUse, args);
    return beanInstance;

4. doCreateBean

真正的實(shí)例化從這里開始

protected Object doCreateBean(){
    BeanWrapper instanceWrapper = null;
    //創(chuàng)建BeanWrapper實(shí)例：實(shí)例化bean
    instanceWrapper = createBeanInstance(beanName, mbd, args);

    // 初始化bean
    Object exposedObject = bean;
    //為bean添加屬性
    populateBean(beanName, mbd, instanceWrapper);
    if (exposedObject != null) {
        exposedObject = initializeBean(beanName, exposedObject, mbd);
    }
     ...
    return exposedObject;
}

5. initializeBean

該方法完成了bean的實(shí)例化：調(diào)用bean的初始化方法：afterPropertiesSet方法蔗牡；調(diào)用PostBeanProcessor的方法生成了增強(qiáng)的bean肾扰。

protected Object initializeBean(){
    //觸發(fā)aware 接口的set方法
    invokeAwareMethods(beanName, bean);
    // PostBeanProcessor方法
    wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
    //調(diào)用初始化方法
    invokeInitMethods(beanName, wrappedBean, mbd);
    wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
    return wrappedBean;
}