用来记录一些原创性的总结
RequestContextUtils类是Spring提供的用于从HttpServletRequest上下文中获取特殊对象的工具类。该工具类虽然是属于Spring的一部分，但是如果在应用中我们有需要直接获取相关信息的需求，我们也可以直接使用。
从request中获取WebApplicationContext。
RequestContextUtils.getWebApplicationContext(request);
从request中获取LocaleResolver或Locale。
RequestContextUtils.getLocaleResolver(request);
RequestContextUtils.getLocale(request);
从request中获取ThemeResolver或Theme。
RequestContextUtils.getThemeResolver(request);
RequestContextUtils.getTheme(request);
除了上面那些，我们还可以获取FlashMapManager和TimeZone等其它信息。以下是该工具类的完整代码。
public abstract class RequestContextUtils {
/**
* Look for the WebApplicationContext associated with the DispatcherServlet
* that has initiated request processing.
* @param request current HTTP request
* @return the request-specific web application context
* @throws IllegalStateException if no servlet-specific context has been found
*/
public static WebApplicationContext getWebApplicationContext(ServletRequest request)
throws IllegalStateException {
return getWebApplicationContext(request, null);
}
/**
* Look for the WebApplicationContext associated with the DispatcherServlet
* that has initiated request processing, and for the global context if none
* was found associated with the current request. This method is useful to
* allow components outside the framework, such as JSP tag handlers,
* to access the most specific application context available.
* @param request current HTTP request
* @param servletContext current servlet context
* @return the request-specific WebApplicationContext, or the global one
* if no request-specific context has been found
* @throws IllegalStateException if neither a servlet-specific nor a
* global context has been found
*/
public static WebApplicationContext getWebApplicationContext(
ServletRequest request, ServletContext servletContext) throws IllegalStateException {
WebApplicationContext webApplicationContext = (WebApplicationContext) request.getAttribute(
DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE);
if (webApplicationContext == null) {
if (servletContext == null) {
throw new IllegalStateException("No WebApplicationContext found: not in a DispatcherServlet request?");
}
webApplicationContext = WebApplicationContextUtils.getRequiredWebApplicationContext(servletContext);
}
return webApplicationContext;
}
/**
* Return the LocaleResolver that has been bound to the request by the
* DispatcherServlet.
* @param request current HTTP request
* @return the current LocaleResolver, or {@code null} if not found
*/
public static LocaleResolver getLocaleResolver(HttpServletRequest request) {
return (LocaleResolver) request.getAttribute(DispatcherServlet.LOCALE_RESOLVER_ATTRIBUTE);
}
/**
* Retrieve the current locale from the given request, using the
* LocaleResolver bound to the request by the DispatcherServlet
* (if available), falling back to the request's accept-header Locale.
* <p>This method serves as a straightforward alternative to the standard
* Servlet {@link javax.servlet.http.HttpServletRequest#getLocale()} method,
* falling back to the latter if no more specific locale has been found.
* <p>Consider using {@link org.springframework.context.i18n.LocaleContextHolder#getLocale()}
* which will normally be populated with the same Locale.
* @param request current HTTP request
* @return the current locale for the given request, either from the
* LocaleResolver or from the plain request itself
* @see #getLocaleResolver
* @see org.springframework.context.i18n.LocaleContextHolder#getLocale()
*/
public static Locale getLocale(HttpServletRequest request) {
LocaleResolver localeResolver = getLocaleResolver(request);
return (localeResolver != null ? localeResolver.resolveLocale(request) : request.getLocale());
}
/**
* Retrieve the current time zone from the given request, using the
* TimeZoneAwareLocaleResolver bound to the request by the DispatcherServlet
* (if available), falling back to the system's default time zone.
* <p>Note: This method returns {@code null} if no specific time zone can be
* resolved for the given request. This is in contrast to {@link #getLocale}
* where there is always the request's accept-header locale to fall back to.
* <p>Consider using {@link org.springframework.context.i18n.LocaleContextHolder#getTimeZone()}
* which will normally be populated with the same TimeZone: That method only
* differs in terms of its fallback to the system time zone if the LocaleResolver
* hasn't provided provided a specific time zone (instead of this method's {@code null}).
* @param request current HTTP request
* @return the current time zone for the given request, either from the
* TimeZoneAwareLocaleResolver or {@code null} if none associated
* @see #getLocaleResolver
* @see org.springframework.context.i18n.LocaleContextHolder#getTimeZone()
*/
public static TimeZone getTimeZone(HttpServletRequest request) {
LocaleResolver localeResolver = getLocaleResolver(request);
if (localeResolver instanceof LocaleContextResolver) {
LocaleContext localeContext = ((LocaleContextResolver) localeResolver).resolveLocaleContext(request);
if (localeContext instanceof TimeZoneAwareLocaleContext) {
return ((TimeZoneAwareLocaleContext) localeContext).getTimeZone();
}
}
return null;
}
/**
* Return the ThemeResolver that has been bound to the request by the
* DispatcherServlet.
* @param request current HTTP request
* @return the current ThemeResolver, or {@code null} if not found
*/
public static ThemeResolver getThemeResolver(HttpServletRequest request) {
return (ThemeResolver) request.getAttribute(DispatcherServlet.THEME_RESOLVER_ATTRIBUTE);
}
/**
* Return the ThemeSource that has been bound to the request by the
* DispatcherServlet.
* @param request current HTTP request
* @return the current ThemeSource
*/
public static ThemeSource getThemeSource(HttpServletRequest request) {
return (ThemeSource) request.getAttribute(DispatcherServlet.THEME_SOURCE_ATTRIBUTE);
}
/**
* Retrieves the current theme from the given request, using the ThemeResolver
* and ThemeSource bound to the request by the DispatcherServlet.
* @param request current HTTP request
* @return the current theme, or {@code null} if not found
* @see #getThemeResolver
*/
public static Theme getTheme(HttpServletRequest request) {
ThemeResolver themeResolver = getThemeResolver(request);
ThemeSource themeSource = getThemeSource(request);
if (themeResolver != null && themeSource != null) {
String themeName = themeResolver.resolveThemeName(request);
return themeSource.getTheme(themeName);
}
else {
return null;
}
}
/**
* Return a read-only {@link Map} with "input" flash attributes saved on a
* previous request.
* @param request the current request
* @return a read-only Map, or {@code null} if not found
* @see FlashMap
*/
@SuppressWarnings("unchecked")
public static Map<String, ?> getInputFlashMap(HttpServletRequest request) {
return (Map<String, ?>) request.getAttribute(DispatcherServlet.INPUT_FLASH_MAP_ATTRIBUTE);
}
/**
* Return the "output" FlashMap with attributes to save for a subsequent request.
* @param request the current request
* @return a {@link FlashMap} instance (never {@code null} within a DispatcherServlet request)
* @see FlashMap
*/
public static FlashMap getOutputFlashMap(HttpServletRequest request) {
return (FlashMap) request.getAttribute(DispatcherServlet.OUTPUT_FLASH_MAP_ATTRIBUTE);
}
/**
* Return the FlashMapManager instance to save flash attributes with
* before a redirect.
* @param request the current request
* @return a {@link FlashMapManager} instance (never {@code null} within a DispatcherServlet request)
*/
public static FlashMapManager getFlashMapManager(HttpServletRequest request) {
return (FlashMapManager) request.getAttribute(DispatcherServlet.FLASH_MAP_MANAGER_ATTRIBUTE);
}
}
（本文是基于Spring4.1.0所写）