Control的调用（续）

接着对于（二）的补充：主要是小结下Control的处理逻辑的关键操作；

对于control的处理关键就是：DispatcherServlet的handlerMappings集合中根据请求的URL匹配每一个handlerMapping对象中的某个handler,匹配成功之后将会返回这个handler的处理连接handlerExecutionChain对象。而这个handlerExecutionChain对象中将会包含用户自定义的多个handlerInterceptor对象。

/**
	 * Return the HandlerExecutionChain for this request.
	 * <p>Tries all handler mappings in order.
	 * @param request current HTTP request
	 * @return the HandlerExecutionChain, or <code>null</code> if no handler could be found
	 */
	protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
		for (HandlerMapping hm : this.handlerMappings) {
			if (logger.isTraceEnabled()) {
				logger.trace(
						"Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
			}
			HandlerExecutionChain handler = hm.getHandler(request);
			if (handler != null) {
				return handler;
			}
		}
		return null;
	}

PS:这么我们需要注意的是：当preHandler返回false时，当前的请求将在执行完afterCompletion后直接返回,handler也将不会执行。

在类HandlerExecutionChain中的getHandler()方法是返回object对象的；

/**
	 * Return the handler object to execute.
	 * @return the handler object
	 */
	public Object getHandler() {
		return this.handler;
	}

/**
	 * Return the handler object to execute.
	 * @return the handler object
	 */
	public Object getHandler() {
		return this.handler;
	}

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Model设计

如果handler兑现返回了ModelAndView对象，那么说明Handler需要传一个Model实例给view去渲染模版。除了渲染页面需要model实例，在业务逻辑层通常也有Model实例。

ModelAndView对象是连接业务逻辑层与view展示层的桥梁，对spring MVC来说它也是连接Handler与view的桥梁。ModelAndView对象顾名思义会持有一个ModelMap对象和一个View对象或者View的名称。ModelMap对象就是执行模版渲染时候所需要的变量对应的实例，如jsp的通过request.getAttribute(String)获取的JSTL标签名对应的对象。velocity中context.get(String)获取$foo对应的变量实例。

public class ModelAndView {

/** View instance or view name String */
	private Object view;

	/** Model Map */
	private ModelMap model;

	/** Indicates whether or not this instance has been cleared with a call to {@link #clear()} */
	private boolean cleared = false;

.....

}

public interface ViewResolver {
	View resolveViewName(String viewName, Locale locale) throws Exception;

}

不同的ViewResolver会对这个Map中的对象有不同的处理方式；

• velocity中将这个Map保存到VelocityContext中。
• JSP中将每一个ModelMap中的元素分别设置到request.setAttribute(modelName,modelValue);

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view设计

在spring MVC中，view模块需要两个组件来支持：RequestToViewNameTranslator和ViewResolver

public interface RequestToViewNameTranslator {

	/**
	 * Translate the given {@link HttpServletRequest} into a view name.
	 * @param request the incoming {@link HttpServletRequest} providing
	 * the context from which a view name is to be resolved
	 * @return the view name (or <code>null</code> if no default found)
	 * @throws Exception if view name translation fails
	 */
	String getViewName(HttpServletRequest request) throws Exception;

}

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RequestToViewNameTranslator：主要支持用户自定义对viewName的解析，如将请求的ViewName加上前缀或者后缀，或者替换成特定的字符串等。

ViewResolver：主要是根据用户请求的viewName创建适合的模版引擎来渲染最终的页面，ViewResolver会根据viewName创建一个view对象，调用view对象的Void render方法渲染出页面；

public interface View {
void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception;
}

dispatcherServlet方法调用getDefaultViewName（）方法；

/**
	 * Translate the supplied request into a default view name.
	 * @param request current HTTP servlet request
	 * @return the view name (or <code>null</code> if no default found)
	 * @throws Exception if view name translation failed
	 */
	protected String getDefaultViewName(HttpServletRequest request) throws Exception {
		return this.viewNameTranslator.getViewName(request);
	}

public interface RequestToViewNameTranslator {

	/**
	 * Translate the given {@link HttpServletRequest} into a view name.
	 * @param request the incoming {@link HttpServletRequest} providing
	 * the context from which a view name is to be resolved
	 * @return the view name (or <code>null</code> if no default found)
	 * @throws Exception if view name translation fails
	 */
	String getViewName(HttpServletRequest request) throws Exception;

}

Locale resolveLocale(HttpServletRequest request);

View resolveViewName(String viewName, Locale locale) throws Exception;