Spring源码情操陶冶-AbstractApplicationContext#initMessageSource

承接前文Spring源码情操陶冶-AbstractApplicationContext#registerBeanPostProcessors
约定web.xml配置的contextClass为默认值XmlWebApplicationContext

瞧瞧官方注释

	/**
	 * Initialize the MessageSource.
	 * Use parent's if none defined in this context.
	 */

初始化MessageSource消息源，如果beanFactory不存在此bean则采用默认的配置并设置父类MessageSource

直接源码

protected void initMessageSource() {
		//获取bean工厂，此处一般为DefaultListableBeanFactory
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		//首先判断是否已有xml文件定义了id为messageSource的bean对象
		if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
			this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
			// Make MessageSource aware of parent MessageSource.
			if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
				//为HierarchicalMessageSource的实现类
				HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
				//设置父类MessageSource，此处设置内部的parent messageSource
				if (hms.getParentMessageSource() == null) {
		hms.setParentMessageSource(getInternalParentMessageSource());
				}
			}
			if (logger.isDebugEnabled()) {
				logger.debug("Using MessageSource [" + this.messageSource + "]");
			}
		}
		else {
			// 则设置默认的DelegatingMessageSource 作为messageSource bean
			DelegatingMessageSource dms = new DelegatingMessageSource();
			dms.setParentMessageSource(getInternalParentMessageSource());
			this.messageSource = dms;
			beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
			if (logger.isDebugEnabled()) {
				logger.debug("Unable to locate MessageSource with name '" + MESSAGE_SOURCE_BEAN_NAME +
						"': using default [" + this.messageSource + "]");
			}
		}
	}

小结

1. 初始化资源配置，如果id为messgeSource的bean在spring xml文件中已配置，则需要注意其class属性为MessageSource的实现类；反之则默认设置DelegatingMessageSource单例资源配置类
2. 如果指定的messageSource类也为HierarchicalMessageSource的实现类则对其设置父类messageSource
3. 此处只涉及到初始化，具体的用途后续补充

下节预告

Spring源码情操陶冶-AbstractApplicationContext#initApplicationEventMulticaster