SpringMVC之RequestContextUtils工具类

RequestContextUtils类

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）