spring 源码学习 初始化(一)

这次算是对以前的一次温习吧,以前对spring的源码理解的也不是很渗透,这次好好系统学习。spring的初始化话,是通过配置文件,然后通过resoure接口加载。

下面我们通过最简单的demo来查看spring源码的执行和设计之美~

applicationContext.xml



	
	

java代码:

public static void main(String[] args){
		
		ApplicationContext  ac=new ClassPathXmlApplicationContext("applicationContext.xml");
		System.out.println(ac.getBean("hello"));
		System.out.println("__________输出实例___________");
	}


看看这个ClassPathXmlApplicationContext的构造函数:


/**
	 * Create a new ClassPathXmlApplicationContext, loading the definitions
	 * from the given XML file and automatically refreshing the context.
	 * @param configLocation resource location
	 * @throws BeansException if context creation failed
	 */
	public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
		this(new String[] {configLocation}, true, null);
	}

解释:是通过加载configLocation这个文件路径applicaton,classpath找到ApplicationContext.xml文件。


继续走:

/**
	 * Create a new ClassPathXmlApplicationContext with the given parent,
	 * loading the definitions from the given XML files.
	 * @param configLocations array of resource locations
	 * @param refresh whether to automatically refresh the context,
	 * loading all bean definitions and creating all singletons.
	 * Alternatively, call refresh manually after further configuring the context.
	 * @param parent the parent context
	 * @throws BeansException if context creation failed
	 * @see #refresh()
	 */
	public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
			throws BeansException {

		super(parent);
		setConfigLocations(configLocations);
		if (refresh) {
			refresh();
		}
	}

configLocations可以加载多个配置文件,这个是spring支持的,refresh这个是判断是否需要刷新applicationcontext,默认是true,parent 这个是父类的ApplicationContext

从这里我们看出,ApplicatonContext 支持多层级关系的context,也就是说从这个层面上来看,我们可以多个project,互通ApplicationContext里面的对象,即使Spring

没有提供这样的扩展,那么我相信Spring肯定会提供这样的扩展接口给开发者。

上面这个是YY的~


然后进入进入setConfigLocations,这个方法主要是给设置配置文件的方法,我先不进去,因为想进入refresh方法看看。


refresh方法内容:


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

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

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



网上看到大牛写的refresh代码介绍,建议看看:


public void refresh() throws BeansException, IllegalStateException {
    // 整个刷新过程是同步的
    synchronized (this.startupShutdownMonitor) {
        // 刷新前的准备工作
        prepareRefresh();
        // 关闭释放旧的beanFactory创建新的beanFactory,读取配置文件等
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
        // 对beanFactory进行一些基本的初始化
        prepareBeanFactory(beanFactory);
 
        try {
            // 下面两行主要用户扩展,处理所有已注册的BeanFactoryPostProcessor,实现在已经加载配置但未初始化bean时对配置进行修改
            postProcessBeanFactory(beanFactory);
            invokeBeanFactoryPostProcessors(beanFactory);
            // 处理所有已注册的BeanPostProcessor,主要用于扩展,实现bean初始化前后的一些定制操作
            registerBeanPostProcessors(beanFactory);
 
            // 初始化消息源bean
            initMessageSource();
            // 初始化事件监听器集,也有人叫事件监听器的注册表,所有的事件监听器都在这个bean里进行管理
            initApplicationEventMulticaster();
            // 主要用于扩展,实现一些特殊bean的初始化,时间点是类似消息源事件监听器集等特殊bean初始化后,普通的bean初始化前
            onRefresh();
            // 注册监听器
            registerListeners();
            // 初始化其余的非延迟加载的单例bean
            finishBeanFactoryInitialization(beanFactory);
 
            // 刷新完成调用LifecycleProcessor的onRefresh方法,并且发布ContextRefreshedEvent事件
            finishRefresh();
        } catch (BeansException ex) {
            // 销毁已经创建的单例bean
            destroyBeans();
            // 重新设置active标记
        cancelRefresh(ex);
            throw ex;
        }
    }
}





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