《Spring源码深度解析》读书笔记 - bean的加载

基本流程

完成了XML配置文件的解析，接下来就是对bean加载的探索。

//2.从ioc容器中获取bean实例
MyTestBean myTestBean = (MyTestBean) beanFactory.getBean("myTestBean");

跟踪进Spring的源码

public Object getBean(String name) throws BeansException {
    return this.doGetBean(name, (Class)null, (Object[])null, false);
}

protected  T doGetBean(String name, Class requiredType, final Object[] args, boolean typeCheckOnly) throws BeansException {
    // 1. 提取对应的beanName
    final String beanName = this.transformedBeanName(name);
    // 2. 直接尝试从缓存获取或者singletonFactories中的ObjectFactory中获取
    Object sharedInstance = this.getSingleton(beanName);
    Object bean;
    if (sharedInstance != null && args == null) {
        if (this.logger.isDebugEnabled()) {
            if (this.isSingletonCurrentlyInCreation(beanName)) {
                this.logger.debug("Returning eagerly cached instance of singleton bean '" + beanName + "' that is not fully initialized yet - a consequence of a circular reference");
            } else {
                this.logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
            }
        }
        // 3.返回对应的实例，有时候存储诸如BeanFactory的情况并不是直接返回实例本身而是返回指定方法返回的实例
        bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, (RootBeanDefinition)null);
    } else {
        // 4.
        if (this.isPrototypeCurrentlyInCreation(beanName)) {
            throw new BeanCurrentlyInCreationException(beanName);
        }

        BeanFactory parentBeanFactory = this.getParentBeanFactory();
        // 5.如果beanDefinitionMap中也就是在所有已经加载的类中不包括beanName，则尝试从parentBeanFactory中检测
        if (parentBeanFactory != null && !this.containsBeanDefinition(beanName)) {
            String nameToLookup = this.originalBeanName(name);
            // 递归到BeanFactory中寻找
            if (args != null) {
                return parentBeanFactory.getBean(nameToLookup, args);
            }

            return parentBeanFactory.getBean(nameToLookup, requiredType);
        }
        // 如果不是仅仅做类型检查则是创建bean，这里要进行记录
        if (!typeCheckOnly) {
            this.markBeanAsCreated(beanName);
        }

        try {
            // 6.将存储XML配置文件的GernericBeanDefinition转换为RootBeanDefinition，如果指定BeanName是子Bean的话同时会合并父类的相关属性
            final RootBeanDefinition mbd = this.getMergedLocalBeanDefinition(beanName);
            this.checkMergedBeanDefinition(mbd, beanName, args);
            String[] dependsOn = mbd.getDependsOn();
            String[] var11;
            // 7.若存在依赖则需要递归实例化依赖的bean
            if (dependsOn != null) {
                var11 = dependsOn;
                int var12 = dependsOn.length;

                for(int var13 = 0; var13 < var12; ++var13) {
                    String dep = var11[var13];
                    if (this.isDependent(beanName, dep)) {
                        throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
                    }
                    // 缓存依赖调用
                    this.registerDependentBean(dep, beanName);
                    this.getBean(dep);
                }
            }
            // 8.singleton模式的创建
            if (mbd.isSingleton()) {
                sharedInstance = this.getSingleton(beanName, new ObjectFactory