整个spring mvc的架构如下图所示：
上篇文件讲解了DispatcherServlet第二步：通过request从Controller获取ModelAndView。现在来讲解第三步：request 从ModelAndView中获取view对象。
获取view对象一般是通过viewResolver来解析view name来完成的。若ModelAndView中view 不存在或者ModelAndView本身为null则填充默认值。代码如下：
ModelAndView中view 不存在或者ModelAndView本身为null
DispatcherServlet doService--->doDispatcher-->applyDefaultViewName(request, mv);
/**
* Do we need view name translation?
*/
private void applyDefaultViewName(HttpServletRequest request, ModelAndView mv) throws Exception {
if (mv != null && !mv.hasView()) {
mv.setViewName(getDefaultViewName(request));
}
}
从request中解析出默认view name
/**
* Translate the supplied request into a default view name.
* @param request current HTTP servlet request
* @return the view name (or {@code null} if no default found)
* @throws Exception if view name translation failed
*/
protected String getDefaultViewName(HttpServletRequest request) throws Exception {
return this.viewNameTranslator.getViewName(request);
}
我们先了解一下这个viewNameTranslator是怎么得到的吧？从容器中获取bean，bean 名称为：DefaultRequestToViewNameTranslator
/**
* Initialize the strategy objects that this servlet uses.
* <p>May be overridden in subclasses in order to initialize further strategy objects.
*/
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
} * Initialize the RequestToViewNameTranslator used by this servlet instance.
* <p>If no implementation is configured then we default to DefaultRequestToViewNameTranslator.
*/
private void initRequestToViewNameTranslator(ApplicationContext context) {
try {
this.viewNameTranslator =
context.getBean(REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME, RequestToViewNameTranslator.class);
if (logger.isDebugEnabled()) {
logger.debug("Using RequestToViewNameTranslator [" + this.viewNameTranslator + "]");
}
}
catch (NoSuchBeanDefinitionException ex) {
// We need to use the default.
this.viewNameTranslator = getDefaultStrategy(context, RequestToViewNameTranslator.class);
if (logger.isDebugEnabled()) {
logger.debug("Unable to locate RequestToViewNameTranslator with name '" +
REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME + "': using default [" + this.viewNameTranslator +
"]");
}
}
}
获取默认view name的真正实现方法如下：
/**
* Translates the request URI of the incoming {@link HttpServletRequest}
* into the view name based on the configured parameters.
* @see org.springframework.web.util.UrlPathHelper#getLookupPathForRequest
* @see #transformPath
*/
@Override
public String getViewName(HttpServletRequest request) {
String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
return (this.prefix + transformPath(lookupPath) + this.suffix);
} /**
* Transform the request URI (in the context of the webapp) stripping
* slashes and extensions, and replacing the separator as required.
* @param lookupPath the lookup path for the current request,
* as determined by the UrlPathHelper
* @return the transformed path, with slashes and extensions stripped
* if desired
*/
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;
}
完整实现如下：
/**
* Return the mapping lookup path for the given request, within the current
* servlet mapping if applicable, else within the web application.
* <p>Detects include request URL if called within a RequestDispatcher include.
* @param request current HTTP request
* @return the lookup path
* @see #getPathWithinApplication
* @see #getPathWithinServletMapping
*/
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);
}
} /**
* Return the path within the servlet mapping for the given request,
* i.e. the part of the request's URL beyond the part that called the servlet,
* or "" if the whole URL has been used to identify the servlet.
* <p>Detects include request URL if called within a RequestDispatcher include.
* <p>E.g.: servlet mapping = "/test/*"; request URI = "/test/a" -> "/a".
* <p>E.g.: servlet mapping = "/test"; request URI = "/test" -> "".
* <p>E.g.: servlet mapping = "/*.test"; request URI = "/a.test" -> "".
* @param request current HTTP request
* @return the path within the servlet mapping, or ""
*/
public String getPathWithinServletMapping(HttpServletRequest request) {
String pathWithinApp = getPathWithinApplication(request);
String servletPath = getServletPath(request);
String 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;
}
} /**
* Return the path within the web application for the given request.
* <p>Detects include request URL if called within a RequestDispatcher include.
* @param request current HTTP request
* @return the path within the web application
*/
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;
}
} /**
* Match the given "mapping" to the start of the "requestUri" and if there
* is a match return the extra part. This method is needed because the
* context path and the servlet path returned by the HttpServletRequest are
* stripped of semicolon content unlike the requesUri.
*/
private String getRemainingPath(String requestUri, String mapping, boolean ignoreCase) {
int index1 = 0;
int index2 = 0;
for (; (index1 < requestUri.length()) && (index2 < mapping.length()); index1++, index2++) {
char c1 = requestUri.charAt(index1);
char c2 = mapping.charAt(index2);
if (c1 == ';') {
index1 = requestUri.indexOf('/', index1);
if (index1 == -1) {
return null;
}
c1 = requestUri.charAt(index1);
}
if (c1 == c2) {
continue;
}
if (ignoreCase && (Character.toLowerCase(c1) == Character.toLowerCase(c2))) {
continue;
}
return null;
}
if (index2 != mapping.length()) {
return null;
}
if (index1 == requestUri.length()) {
return "";
}
else if (requestUri.charAt(index1) == ';') {
index1 = requestUri.indexOf('/', index1);
}
return (index1 != -1 ? requestUri.substring(index1) : "");
}
ModelAndView中view 定义为view name，解析为view实例。
DispatcherServlet doService--->doDispatcher-->processDispatchResult--->render--->resolveViewName
/**
* Resolve the given view name into a View object (to be rendered).
* <p>The default implementations asks all ViewResolvers of this dispatcher.
* Can be overridden for custom resolution strategies, potentially based on
* specific model attributes or request parameters.
* @param viewName the name of the view to resolve
* @param model the model to be passed to the view
* @param locale the current locale
* @param request current HTTP servlet request
* @return the View object, or {@code null} if none found
* @throws Exception if the view cannot be resolved
* (typically in case of problems creating an actual View object)
* @see ViewResolver#resolveViewName
*/
protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale,
HttpServletRequest request) throws Exception { for (ViewResolver viewResolver : this.viewResolvers) {
View view = viewResolver.resolveViewName(viewName, locale);
if (view != null) {
return view;
}
}
return null;
}
InternalResourceViewResolver是具体实现：
@Override
protected AbstractUrlBasedView buildView(String viewName) throws Exception {
InternalResourceView view = (InternalResourceView) super.buildView(viewName);
if (this.alwaysInclude != null) {
view.setAlwaysInclude(this.alwaysInclude);
}
if (this.exposeContextBeansAsAttributes != null) {
view.setExposeContextBeansAsAttributes(this.exposeContextBeansAsAttributes);
}
if (this.exposedContextBeanNames != null) {
view.setExposedContextBeanNames(this.exposedContextBeanNames);
}
view.setPreventDispatchLoop(true);
return view;
}
/**
* Creates a new View instance of the specified view class and configures it.
* Does <i>not</i> perform any lookup for pre-defined View instances.
* <p>Spring lifecycle methods as defined by the bean container do not have to
* be called here; those will be applied by the {@code loadView} method
* after this method returns.
* <p>Subclasses will typically call {@code super.buildView(viewName)}
* first, before setting further properties themselves. {@code loadView}
* will then apply Spring lifecycle methods at the end of this process.
* @param viewName the name of the view to build
* @return the View instance
* @throws Exception if the view couldn't be resolved
* @see #loadView(String, java.util.Locale)
*/
protected AbstractUrlBasedView buildView(String viewName) throws Exception {
AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(getViewClass());
view.setUrl(getPrefix() + viewName + getSuffix());
String contentType = getContentType();
if (contentType != null) {
view.setContentType(contentType);
}
view.setRequestContextAttribute(getRequestContextAttribute());
view.setAttributesMap(getAttributesMap());
Boolean exposePathVariables = getExposePathVariables();
if (exposePathVariables != null) {
view.setExposePathVariables(exposePathVariables);
}
return view;
}
ModelAndView 本身存在view实例
// No need to lookup: the ModelAndView object contains the actual View object.
view = mv.getView();
不需要查询，使用getView方法即可获取到。
小结：
本文主要讲解request怎么从ModelAndView中获取view实例的，分三种情况：mv本身为空或者mv中view为空时，使用默认的view name；mv本身中view 为string 表示viewname而非view实例，那么根据view name使用viewResolver转换成view实例；mv本身有view实例则使用getview方法获取。