Spring IOC 源码分析

0.预配置环境

请参考上一篇

 

1.启动类

public class Application {

    public static void main(String[] args) {
        // 创建Spring容器，从这里开始debug
        ApplicationContext context = new ClassPathXmlApplicationContext("classpath:application.xml");
        System.out.println("context 启动成功");
        // 获取bean
        MessageService messageService = context.getBean(MessageService.class);
        System.out.println(messageService.getMessage());
    }
}

2.ClassPathXmlApplicationContext的继承体系

3.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
	 */
    // 我们直接使用的这个构造函数，内部调用下面构造函数
	public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
		this(new String[] {configLocation}, true, null);
	}

	
    /**
	 * 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 {
            // 初始化父类
            // 看到初始化app类加载器
		super(parent);
            // 保存配置文件的位置 其实开始传入的参数
		setConfigLocations(configLocations);
		if (refresh) {
                // 重头戏 refresh
			refresh();
		}
	}

开始进入重点

ClassPathXmlApplicationContext 类的构造函数中调用父类 AbstractApplicationContext.refresh() 方法

4.refresh 方法源码

    @Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
            // 设置**标识active  里面预存了一个回调函数
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
            // 重点
            // 
			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) {
				if (logger.isWarnEnabled()) {
					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;
			}

			finally {
				// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				resetCommonCaches();
			}
		}
	}

 

	/**
	 * Tell the subclass to refresh the internal bean factory.
	 * @return the fresh BeanFactory instance
	 * @see #refreshBeanFactory()
	 * @see #getBeanFactory()
	 */
    // 通知子类AbstractRefreshableApplicationContext刷新beanFactory
	protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        // 重点
        // 
		refreshBeanFactory();
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		if (logger.isDebugEnabled()) {
			logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
		}
		return beanFactory;
	}

/**
	 * This implementation performs an actual refresh of this context's underlying
	 * bean factory, shutting down the previous bean factory (if any) and
	 * initializing a fresh bean factory for the next phase of the context's lifecycle.
	 */
	@Override
	protected final void refreshBeanFactory() throws BeansException {
        // 如果beanFactory 已经存在，则销毁单例的bean,关闭beanFactory
		if (hasBeanFactory()) {
			destroyBeans();
			closeBeanFactory();
		}
		try {
            // 创建 DefaultListableBeanFactory
            // DefaultListableBeanFactory 是beanFactory体系里相当重要且常用的一个beanFactory
			DefaultListableBeanFactory beanFactory = createBeanFactory();
			beanFactory.setSerializationId(getId());
                    // 设置beanFactory 是否支持 bean定义的覆盖，bean的循环引用。默认两个都是true 
			customizeBeanFactory(beanFactory);
            // 重点
            // 解析beanDefinitions
			loadBeanDefinitions(beanFactory);
			synchronized (this.beanFactoryMonitor) {
				this.beanFactory = beanFactory;
			}
		}
		catch (IOException ex) {
			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
		}
	}

DefaultListableBeanFactory 的继承体系

 

xml方式加载bean定义

	/**
	 * Loads the bean definitions via an XmlBeanDefinitionReader.
	 * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
	 * @see #initBeanDefinitionReader
	 * @see #loadBeanDefinitions
	 */
                // 加载bean定义
	@Override
	protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
		// Create a new XmlBeanDefinitionReader for the given BeanFactory.
		XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

		// Configure the bean definition reader with this context's
		// resource loading environment.
		beanDefinitionReader.setEnvironment(this.getEnvironment());
		beanDefinitionReader.setResourceLoader(this);
		beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

		// Allow a subclass to provide custom initialization of the reader,
		// then proceed with actually loading the bean definitions.
		initBeanDefinitionReader(beanDefinitionReader);
        // 重点
		loadBeanDefinitions(beanDefinitionReader);
	}

 

	/**
	 * Load the bean definitions with the given XmlBeanDefinitionReader.
	 * <p>The lifecycle of the bean factory is handled by the {@link #refreshBeanFactory}
	 * method; hence this method is just supposed to load and/or register bean definitions.
	 * @param reader the XmlBeanDefinitionReader to use
	 * @throws BeansException in case of bean registration errors
	 * @throws IOException if the required XML document isn't found
	 * @see #refreshBeanFactory
	 * @see #getConfigLocations
	 * @see #getResources
	 * @see #getResourcePatternResolver
	 */
	protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
        // 通过资源文件加载
		Resource[] configResources = getConfigResources();
		if (configResources != null) {
			reader.loadBeanDefinitions(configResources);
		}
                    // 通过配置文件的位置加载
		String[] configLocations = getConfigLocations();
		if (configLocations != null) {
			reader.loadBeanDefinitions(configLocations);
		}
	}

 

/**
	 * Load bean definitions from the specified resource location.
	 * <p>The location can also be a location pattern, provided that the
	 * ResourceLoader of this bean definition reader is a ResourcePatternResolver.
	 * @param location the resource location, to be loaded with the ResourceLoader
	 * (or ResourcePatternResolver) of this bean definition reader
	 * @param actualResources a Set to be filled with the actual Resource objects
	 * that have been resolved during the loading process. May be {@code null}
	 * to indicate that the caller is not interested in those Resource objects.
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException in case of loading or parsing errors
	 * @see #getResourceLoader()
	 * @see #loadBeanDefinitions(org.springframework.core.io.Resource)
	 * @see #loadBeanDefinitions(org.springframework.core.io.Resource[])
	 */
	public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
		ResourceLoader resourceLoader = getResourceLoader();
		if (resourceLoader == null) {
			throw new BeanDefinitionStoreException(
					"Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
		}

		if (resourceLoader instanceof ResourcePatternResolver) {
			// Resource pattern matching available.
			try {
				Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
				int loadCount = loadBeanDefinitions(resources);
				if (actualResources != null) {
					for (Resource resource : resources) {
						actualResources.add(resource);
					}
				}
				if (logger.isDebugEnabled()) {
					logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
				}
				return loadCount;
			}
			catch (IOException ex) {
				throw new BeanDefinitionStoreException(
						"Could not resolve bean definition resource pattern [" + location + "]", ex);
			}
		}
		else {
			// Can only load single resources by absolute URL.
			Resource resource = resourceLoader.getResource(location);
			int loadCount = loadBeanDefinitions(resource);
			if (actualResources != null) {
				actualResources.add(resource);
			}
			if (logger.isDebugEnabled()) {
				logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
			}
			return loadCount;
		}
	}