spring－容器5－bean初始化及依赖注入

容器初始化总体流程

一 入口

• beanFactory接口getBean初始化并返回对应bean

public Object getBean(String name) throws BeansException {
    return doGetBean(name, null, null, false);
}

• 1 从单例bean三级缓存中依次尝试获取单例bean

• 2 缓存获取成功，普通bean或想获取factorybean(name前缀有&)则直接返回。 否则调用getObject()获取factoryBean对应的实际bean。

• 3 原型模式不支持循环依赖，若创建中则抛异常

• 4 当前factory中没找到则尝试到父factory中获取bean

• 5 若配置了依赖bean，则先创建依赖bean

• 6 单例bean，则获取bean，并同步骤2获取实际bean

• 7 原型bean，获取bean之前标记，获取bean之后删除标记。用于步骤3中控制避免循环依赖。获取bean之后处理同步骤2

• 8 范围bean，处理同原型bean。

• 9 指定类型，则进行类型转换

protected  T doGetBean(
        final String name, final Class requiredType, final Object[] args, boolean typeCheckOnly)
        throws BeansException {
    final String beanName = transformedBeanName(name);
    Object bean;
    Object sharedInstance = getSingleton(beanName);//1
    if (sharedInstance != null && args == null) {//2
        if (logger.isDebugEnabled()) {
            if (isSingletonCurrentlyInCreation(beanName)) {
                logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
                        "' that is not fully initialized yet - a consequence of a circular reference");
            }
            else {
                logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
            }
        }
        bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
    }
    else {
        if (isPrototypeCurrentlyInCreation(beanName)) {//3
            throw new BeanCurrentlyInCreationException(beanName);
        }

        BeanFactory parentBeanFactory = getParentBeanFactory();
        if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {//4
            String nameToLookup = originalBeanName(name);
            if (args != null) {
                return (T) parentBeanFactory.getBean(nameToLookup, args);
            }
            else {
                return parentBeanFactory.getBean(nameToLookup, requiredType);
            }
        }

        if (!typeCheckOnly) {
            markBeanAsCreated(beanName);
        }

        try {
            final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
            checkMergedBeanDefinition(mbd, beanName, args);

            String[] dependsOn = mbd.getDependsOn();//5
            if (dependsOn != null) {
                for (String dependsOnBean : dependsOn) {
                    if (isDependent(beanName, dependsOnBean)) {
                        throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                "Circular depends-on relationship between '" + beanName + "' and '" + dependsOnBean + "'");
                    }
                    registerDependentBean(dependsOnBean, beanName);
                    getBean(dependsOnBean);
                }
            }

            if (mbd.isSingleton()) {//6
                sharedInstance = getSingleton(beanName, new ObjectFactory