白话Spring源码（十三）：Spring Context源码分析

客官°小女子只卖身不卖艺 2022-02-16 17:27 286阅读 0赞

前几篇博客给大家介绍了Spring框架的IOC和AOP的源码，那怎么把这两个核心组件连接起来对外提供更好用的接口呢？这时context包里的ApplicationContext就登场了。

### 简单使用 ###

我们先看个ApplicationContext使用的demo：

ClassPathXmlApplicationContext context=new ClassPathXmlApplicationContext("bean.xml");
    Person person=(Person)context.getBean("person");
    person.sayHello();

就是这么简单，ApplicationContext封装了IOC和AOP的两大核心功能，对外提交了简单的接口。

### 分析源码 ###

我们先看ClassPathXmlApplicationContext的源码：

public class ClassPathXmlApplicationContext extends AbstractXmlApplicationContext {
    
    	private String[] configLocations;
    
    
    	public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
    		this.configLocations = new String[] {configLocation};
    		refresh();
    	}
    
    
    	public ClassPathXmlApplicationContext(String[] configLocations) throws BeansException {
    		this.configLocations = configLocations;
    		refresh();
    	}
    
    
    	public ClassPathXmlApplicationContext(String[] configLocations, ApplicationContext parent)
    			throws BeansException {
    		super(parent);
    		this.configLocations = configLocations;
    		refresh();
    	}
    
    	protected String[] getConfigLocations() {
    		return this.configLocations;
    	}
    
    }

这里关键代码都在refresh()里

public abstract class AbstractApplicationContext extends DefaultResourceLoader
    		implements ConfigurableApplicationContext {
    
    其他代码
    
    	public void refresh() throws BeansException {
    		this.startupTime = System.currentTimeMillis();
    
    		// 加载BeanFactory，子类去实现
    		refreshBeanFactory();
    		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    
    		beanFactory.registerCustomEditor(Resource.class, new ContextResourceEditor(this));
    		beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
    		beanFactory.ignoreDependencyType(ResourceLoader.class);
    		beanFactory.ignoreDependencyType(ApplicationContext.class);
    		postProcessBeanFactory(beanFactory);
    
    		// invoke factory processors registered with the context instance
    		for (Iterator it = getBeanFactoryPostProcessors().iterator(); it.hasNext();) {
    			BeanFactoryPostProcessor factoryProcessor = (BeanFactoryPostProcessor) it.next();
    			factoryProcessor.postProcessBeanFactory(beanFactory);
    		}
    
    		if (getBeanDefinitionCount() == 0) {
    			logger.warn("No beans defined in ApplicationContext [" + getDisplayName() + "]");
    		}
    		else {
    			logger.info(getBeanDefinitionCount() + " beans defined in ApplicationContext [" + getDisplayName() + "]");
    		}
    
    		// 执行BeanFactory的PostProcessors
    		invokeBeanFactoryPostProcessors();
    
    		// 注册bean的beanProcessors实现拦截器，AOP
    		registerBeanPostProcessors();
    
    		// 初始化MessageSource，支持国际化
    		initMessageSource();
    
    		// 调用子类里的自定义刷新代码
    		onRefresh();
    
    		// 加载所有监听器
    		refreshListeners();
    
    		// 预处理单例
    		beanFactory.preInstantiateSingletons();
    
    		// 调用上下文刷新事件
    		publishEvent(new ContextRefreshedEvent(this));
    	}
    
    }

AbstractXmlApplicationContext里的refreshBeanFactory

protected void refreshBeanFactory() throws BeansException {
    		try {
    			DefaultListableBeanFactory beanFactory = createBeanFactory();
    			XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
    			beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
    			initBeanDefinitionReader(beanDefinitionReader);
    			loadBeanDefinitions(beanDefinitionReader);
    			this.beanFactory = beanFactory;
    			if (logger.isInfoEnabled()) {
    				logger.info("Bean factory for application context '" + getDisplayName() + "': " + beanFactory);
    			}
    		}
    		catch (IOException ex) {
    			throw new ApplicationContextException("I/O error parsing XML document for application context [" +
    			                                      getDisplayName() + "]", ex);
    		} 
    	}

这里封装了IOC的核心实现代码，看过IOC源码的应该很容易看懂，可以看我前几篇关于IOC的博客！

我们在前面介绍AOP的博客里知道AOP主要是通过BeanPostProcessor接口实现的，在refresh()方法里调用了registerBeanPostProcessors()

private void registerBeanPostProcessors() throws BeansException {
    		String[] beanNames = getBeanDefinitionNames(BeanPostProcessor.class);
    		if (beanNames.length > 0) {
    			List beanProcessors = new ArrayList();
    			for (int i = 0; i < beanNames.length; i++) {
    				beanProcessors.add(getBean(beanNames[i]));
    			}
    			Collections.sort(beanProcessors, new OrderComparator());
    			for (Iterator it = beanProcessors.iterator(); it.hasNext();) {
    				getBeanFactory().addBeanPostProcessor((BeanPostProcessor) it.next());
    			}
    		}
    	}

好了，现在我们知道context的主要作用是封装Spring的IOC和AOP两大核心功能，对外提供接口，其实这也类似设计模式里的门面模式！

下篇博客重点给大家介绍context的又一个核心功能：事件机制。