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。