Spring源码分析（二）-Spring IoC容器的初始化No.1

Spring IoC容器的初始化

Spring源码分析（一）中提到了很多类，比如BeanDefinition、BeanDefinitionReader、BeanDefintionParser、BeanWrapper等都是ApplicationContext中需要使用的类，都可以从Spring源码中的注释中了解

IoC容器的初始化时由前面介绍的AbstractApplicationContext.refresh方法来启动的，具体来说，这个启动包括Bean的加载过程和Bean的实例化过程：

• Bean的加载过程分为，BeanDefinition的Resource定位、载入和注册
• Bean的实例化过程分为，Bean的创建和依赖注入

refresh()源码：

    @Override
    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // Prepare this context for refreshing.
            prepareRefresh();

            // Tell the subclass to refresh the internal bean factory.
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // Prepare the bean factory for use in this context.
            prepareBeanFactory(beanFactory);

            try {
                // Allows post-processing of the bean factory in context subclasses.
                postProcessBeanFactory(beanFactory);

                // Invoke factory processors registered as beans in the context.
                invokeBeanFactoryPostProcessors(beanFactory);

                // Register bean processors that intercept bean creation.
                registerBeanPostProcessors(beanFactory);

                // Initialize message source for this context.
                initMessageSource();

                // Initialize event multicaster for this context.
                initApplicationEventMulticaster();

                // Initialize other special beans in specific context subclasses.
                onRefresh();

                // Check for listener beans and register them.
                registerListeners();

                // Instantiate all remaining (non-lazy-init) singletons.
                finishBeanFactoryInitialization(beanFactory);

                // Last step: publish corresponding event.
                finishRefresh();
            }

            catch (BeansException ex) {
                logger.warn("Exception encountered during context initialization - cancelling refresh attempt", ex);

                // Destroy already created singletons to avoid dangling resources.
                destroyBeans();

                // Reset 'active' flag.
                cancelRefresh(ex);

                // Propagate exception to caller.
                throw ex;
            }
        }
    }

Bean加载过程

BeanDefinition的Resource定位

实现路径：refresh()=>obtainFreshBeanFactory()=>refreshBeanFactory(）=>loadBeanDefinitions()….DefaultResourceLoader.getResource()
这个Resource定位指的是BeanDefinition的资源定位，它由ResourceLoader完成的

BeanDefinition的载入和解析

这个过程是把用户定义好的Bean表示成IoC容器内部的数据结构，即BeanDefinition
实现路径：refresh()=>obtainFreshBeanFactory()=>refreshBeanFactory(）=>loadBeanDefinitions()
其中牵扯到很多类，XmlBeanDefinitionReader、BeanDefinitionParserDelegate等等，可以DeBug进去
最后会发现Spring也是用的ClassLoader加载的class文件，将class信息封装成BeanDefinition

BeanDefinition在IoC容器中注册

实现路径：refresh()=>obtainFreshBeanFactory()=>refreshBeanFactory(）=>loadBeanDefinitions()……DefaultListableBeanFactory.registerBeanDefinition
最终DeBug的话会调到该方法，哎，只能说Spring好深，DefaultListableBeanFactory继承了BeanDefinitionRegistry接口，处处可以发现Spring面向接口的编程思想，职责分明

    /** Map of bean definition objects, keyed by bean name */
    private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(64);

所有的BeanDefinition都会存放在这个ConcurrentHashMap中

总结

至此Bean的加载过程到此结束，下一章重点分析bean的实例化和依赖注入

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