Spring Bean实例化过程详解

且挨过三冬四夏，暂受些此痛苦。雪尽后再看梅花。

这篇讲解SpringBean实例化过程的关键代码,代码目录可以查找上篇。

首先是getBean->doGetBean

final String beanName = this.transformedBeanName(name);

这里传入的名称可能是别名,做别名解析

    protected Object getSingleton(String beanName, boolean allowEarlyReference) {
        Object singletonObject = this.singletonObjects.get(beanName);
        if (singletonObject == null && this.isSingletonCurrentlyInCreation(beanName)) {
            synchronized(this.singletonObjects) {
                singletonObject = this.earlySingletonObjects.get(beanName);
                if (singletonObject == null && allowEarlyReference) {
                    ObjectFactory singletonFactory = (ObjectFactory)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;
    }

走到getSingleton()去缓存池中获取对象,如果singletonObjects和earlySingletonObjects中都没有且singletonFactories里有,会调用getObject()方法获取早期对象,并放入earlySingletonObjects且从singletonFactories中移除包装对象。

bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, (RootBeanDefinition)null);

如果获取到了对象,调用getObjectForBeanInstance处理这里可能是工厂Bean的情况,然后直接返回bean并结束

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

如果没有获取到对象,则尝试获取父工厂,如果父工厂不为空且当前容易不包含他的bean定义,那么走父工厂的创建流程(回到开始)

final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);

合并Bean定义,如果存在父Bean是一个抽象Bean

checkMergedBeanDefinition(mbd, beanName, args);

校验当前bean定义不能为抽象

registerDependentBean(dep, beanName);

解析depend-on的bean,如果依赖其他bean需要先创建依赖的bean,这个时候如果A dependon B,B dependon A,会报错

然后根据scope类型来创建Bean,这里只解析单例bean,因为其他类型的都不由spring管理其生命周期

sharedInstance = this.getSingleton(beanName, new ObjectFactory