Spring之SpringMVC的RequestToViewNameTranslator(源码)分析

前言

　　SpringMVC如果在处理业务的过程中发生了异常，这个时候是没有一个完整的ModelAndView对象返回的，它应该是怎么样处理呢？或者说应该怎么去获取一个视图然后去展示呢。下面就是要讲的RequestToViewNameTranslator。

1.引出问题

　　DispathcerServlet在处理完请求获取Me的lAndView之后就会获取相应的视图名称，然后渲染解析。这个是通过调用doDispatch()中的processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);方法来完成的，但是如果在处理这个请求的过程中发生了异常，并且这个异常类型不是ModelAndViewDefiningException类型的话，就会调用processHandlerException来处理一个异常，返回默认缺省的视图：

	protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
			Object handler, Exception ex) throws Exception {

		// Check registered HandlerExceptionResolvers...
		ModelAndView exMv = null;
		for (HandlerExceptionResolver handlerExceptionResolver : this.handlerExceptionResolvers) {
			exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);
			if (exMv != null) {
				break;
			}
		}
		if (exMv != null) {
			if (exMv.isEmpty()) {
				return null;
			}
			// We might still need view name translation for a plain error model...
			if (!exMv.hasView()) {
				exMv.setViewName(getDefaultViewName(request));
			}
			if (logger.isDebugEnabled()) {
				logger.debug("Handler execution resulted in exception - forwarding to resolved error view: " + exMv, ex);
			}
			WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
			return exMv;
		}

		throw ex;
	}

　　在处理的过程中有这么一个需要注意exMv.setViewName(getDefaultViewName(request));如果没有提供的视图名字，那么胸膛会根据请求来获取一个默认的视图名。来看下具体获取默认视图的过程。

protected String getDefaultViewName(HttpServletRequest request) throws Exception {
		return this.viewNameTranslator.getViewName(request);
	}

　　原来是通过RequestToViewNameTranslator viewNameTranslator;的getViewName来获取视图名称的。终于讲到今天的主角RequestToViewNameTranslator接口及其的默认实现类DefaultRequestToViewNameTranslator。

2.RequestToViewNameTranslator接口

首先看源码，

public interface RequestToViewNameTranslator {

	String getViewName(HttpServletRequest request) throws Exception;

}

　　这个接口只有一个方法，就是根据请求对象获取一个视图名称。具体来讲就是在没有明确指定一个视图名称的时候，根据一个输入的请求获取一个逻辑视图名称。

3.DefaultRequestToViewNameTranslator实现

作为RequestToViewNameTranslator接口唯一的实现类，在没有扩展指定接口时候的时候，系统就会加载这个作为默认的实现。来看看具体时候涉及到的实现代码，

public String getViewName(HttpServletRequest request) {
		String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
		return (this.prefix + transformPath(lookupPath) + this.suffix);
	}

	protected String transformPath(String lookupPath) {
		String path = lookupPath;
		if (this.stripLeadingSlash && path.startsWith(SLASH)) {
			path = path.substring(1);
		}
		if (this.stripTrailingSlash && path.endsWith(SLASH)) {
			path = path.substring(0, path.length() - 1);
		}
		if (this.stripExtension) {
			path = StringUtils.stripFilenameExtension(path);
		}
		if (!SLASH.equals(this.separator)) {
			path = StringUtils.replace(path, SLASH, this.separator);
		}
		return path;
	}

　　主要实现就是调用UrlPathHelper的getLookupPathForRequest的方法获取一个looup路径。transformPath方法主要是对获取的路径字符串再做个简单处理罢了。主要是UrlPathHelper的getLookupPathForRequest的实现：

	public String getLookupPathForRequest(HttpServletRequest request) {
		// Always use full path within current servlet context?
		if (this.alwaysUseFullPath) {
			return getPathWithinApplication(request);
		}
		// Else, use path within current servlet mapping if applicable
		String rest = getPathWithinServletMapping(request);
		if (!"".equals(rest)) {
			return rest;
		}
		else {
			return getPathWithinApplication(request);
		}
	}

	public String getPathWithinApplication(HttpServletRequest request) {
		String contextPath = getContextPath(request);
		String requestUri = getRequestUri(request);
		String path = getRemainingPath(requestUri, contextPath, true);
		if (path != null) {
			// Normal case: URI contains context path.
			return (StringUtils.hasText(path) ? path : "/");
		}
		else {
			return requestUri;
		}
	}
	public String getPathWithinServletMapping(HttpServletRequest request) {
		String pathWithinApp = getPathWithinApplication(request);
		String servletPath = getServletPath(request);
		String sanitizedPathWithinApp = getSanitizedPath(pathWithinApp);
		String path;

		// if the app container sanitized the servletPath, check against the sanitized version
		if(servletPath.indexOf(sanitizedPathWithinApp) != -1) {
			path = getRemainingPath(sanitizedPathWithinApp, servletPath, false);
		}
		else {
			path = getRemainingPath(pathWithinApp, servletPath, false);
		}

		if (path != null) {
			// Normal case: URI contains servlet path.
			return path;
		}
		else {
			// Special case: URI is different from servlet path.
			String pathInfo = request.getPathInfo();
			if (pathInfo != null) {
				// Use path info if available. Indicates index page within a servlet mapping?
				// e.g. with index page: URI="/", servletPath="/index.html"
				return pathInfo;
			}
			if (!this.urlDecode) {
				// No path info... (not mapped by prefix, nor by extension, nor "/*")
				// For the default servlet mapping (i.e. "/"), urlDecode=false can
				// cause issues since getServletPath() returns a decoded path.
				// If decoding pathWithinApp yields a match just use pathWithinApp.
				path = getRemainingPath(decodeInternal(request, pathWithinApp), servletPath, false);
				if (path != null) {
					return pathWithinApp;
				}
			}
			// Otherwise, use the full servlet path.
			return servletPath;
		}
	}

	public String getPathWithinApplication(HttpServletRequest request) {
		String contextPath = getContextPath(request);
		String requestUri = getRequestUri(request);
		String path = getRemainingPath(requestUri, contextPath, true);
		if (path != null) {
			// Normal case: URI contains context path.
			return (StringUtils.hasText(path) ? path : "/");
		}
		else {
			return requestUri;
		}
	}

　　

　　首先判断当前上下文的完整路径是否为空，如果不为空就会调用getPathWithinApplication（）方法返回这个路径名字。如果为空的话，则首先获取到当前请求的映射的完整路径，如果路径不为空就返回这个路径，如果路径为空则返回当前请求的完整路径了。