SpringMVC之RequestContextUtils工具类

ゝ一世哀愁。 2022-03-11 05:16 42阅读 0赞

# 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）