22_3 Spring MVC - ViewResolver系列 - XmlViewResolver

22_3 Spring MVC - ViewResolver系列 - XmlViewResolver

一、简介

XmlViewResolver是XML视图解析器，它实现了ViewResolver接口，接收相同DTD定义的xml配置文件定义的视图Bean对象。

二、源码解析

在XmlViewResolver 直接实现了 抽象方法 loadView来完成View的创建

2.1 loadView

	@Override
	protected View loadView(String viewName, Locale locale) throws BeansException {
		BeanFactory factory = initFactory();
		try {
			return factory.getBean(viewName, View.class);
		}
		catch (NoSuchBeanDefinitionException ex) {
			// Allow for ViewResolver chaining...
			return null;
		}
	}

• 先通过 initFactory 初始化Spring容器
• 然后使用创建的Spring容器根据 视图名称创建一个View并返回

2.2 initFactory()

	
	public static final String DEFAULT_LOCATION = "/WEB-INF/views.xml";

	protected synchronized BeanFactory initFactory() throws BeansException {
		if (this.cachedFactory != null) {
			return this.cachedFactory;
		}

		ApplicationContext applicationContext = obtainApplicationContext();

		Resource actualLocation = this.location;
        // 如果不指定XmlViewResolver的配置文件，则使用默认的
		if (actualLocation == null) {
			actualLocation = applicationContext.getResource(DEFAULT_LOCATION);
		}

		// Create child ApplicationContext for views.
		GenericWebApplicationContext factory = new GenericWebApplicationContext();
		factory.setParent(applicationContext);
		factory.setServletContext(getServletContext());

		// Load XML resource with context-aware entity resolver.
		XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
		reader.setEnvironment(applicationContext.getEnvironment());
		reader.setEntityResolver(new ResourceEntityResolver(applicationContext));
		reader.loadBeanDefinitions(actualLocation);

		factory.refresh();

		if (isCache()) {
			this.cachedFactory = factory;
		}
		return factory;
	}

• 创建 XmlBeanDefinitionReader 对象
• 通过 reader.loadBeanDefinitions(actualLocation); 方法加载xml配置文件
• 可以看到如果不指定XmlViewResolver的配置文件，那么默认配置文件是 /WEB-INF/views.xml 这个文件

三、使用方法

3.1 配置视图解析器

<bean id="viewResolver" class="org.springframework.web.servlet.view.XmlViewResolver">
    <property name="location" value="/WEB-INF/views.xml"></property> 
</bean>

3.2 配置视图配置文件views.xml里各项的配置

<bean id="parent-view" class="org.springframework.web.servlet.view.JstlView">
   <property name="attributes">
     <props>   <prop key="title">FlightDeals.com</prop>  <prop key="season">Summer</prop>
    </props>
  </property>
	<property name="url" value="/index.jsp"></property>
</bean>

<bean id="home" parent="parent-view">
   <property name="url" value="/WEB-INF/jsp/home.jsp"/>
</bean>

<bean id="listFlight" parent="parent-view">
   <property name="url" value="/WEB-INF/jsp/listFlights.jsp"/>
</bean>

• 当Controller返回的视图名是 home或者 listFlight时，根据定义的id寻找匹配的View这里是JstlView
• 按照匹配的url的属性值，使用JstlView去解析属性值进行视图的解析，将最终的视图页面展示给用户