LanguageShuntFactory produces Shunts which determine mode based * on the Accept-Language header submitted by the user agent. * *
Modes can be specified as "en", "fr", "zh-hk", and the like. * Multiple modes can be assigned to the same view by comma-delimiting * them ("en,fr"). In addition, a view can leave its mode unspecified * to be a "default" view which will apply when no other mode is * appropriate.
* *Choosing mode from a request attribute "language" is done by * setting * request attribute.
* *E.g. request.setAttribute("language", "en");
* *Default mode can be provided using ShuntingFactory attribute * "default-language".
* *** ** ** **
It is not required to user to supply "default-language" attribute * or to set request attribute "language". If these are not supplied then * the procedure follows as described below. Accept-Language headers are * also used if request attribute "language" or "default-language" does * not give a proper View.
* *Choosing mode from the Accept-Language header follows the way * browsers actually work rather than the HTTP spec. Go figure. There * is no support for quality levels and preference is determined by * simple order in the string. Furthermore, there is some magic regarding * prefixed languages: After trying each of the languages specified, * any prefixed languages are chopped one level and tried again. This * process is repeated until nothing is left to try but the null mode.
* *For an example Accept-Language header "fr,zh-tw,zh-hk,no-nynorsk", * the Shunt will check for modes in this order:
* *Hopefully this produces useful behavior.
*/ public class LanguageShuntFactory implements ShuntFactory { /** * This is used to provide default language for web application */ protected final static String ATTR_DEFAULT_LANGUAGE = "default-language"; protected String defaultLanguage; public final static String KEY_REQUEST_LANGUAGE = "language"; /** */ class LanguageShunt implements Shunt { /** */ protected Map modes = new HashMap(); /** * All modes are converted to lower case and trimmed. * Note that multiple modes can be specified as a * comma-delimited sequence, all aliased to the same view. */ public void defineMode(String mode, View v) throws ConfigException { if (mode == null) this.reallyDefineMode(null, v); else { mode = mode.toLowerCase(); StringTokenizer tokens = new StringTokenizer(mode, ","); while (tokens.hasMoreTokens()) { mode = tokens.nextToken().trim(); this.reallyDefineMode(mode, v); } } } /** * Does not attempt to interpret mode, but checks for duplicates. */ protected void reallyDefineMode(String mode, View v) throws ConfigException { if (this.modes.containsKey(mode)) throw new ConfigException("A duplicate mode (" + mode + ") was" + " specified in a view. Note that language modes" + " are case insensitive."); this.modes.put(mode, v); } /** */ public View getView(HttpServletRequest request) throws NoSuitableModeException { String requestedLanguage; // At first try to find a mode for requested language if (request.getAttribute(KEY_REQUEST_LANGUAGE) != null) { requestedLanguage = request.getAttribute(KEY_REQUEST_LANGUAGE).toString(); View theView = (View) modes.get(requestedLanguage); if (theView != null) { log.debug("Using mode: " + requestedLanguage); return theView; } } // Next we try to determine if there exist mode for default language if (defaultLanguage != null) { View theView = (View) modes.get(defaultLanguage); if (theView != null) { log.debug("Using mode: " + defaultLanguage); return theView; } } // And finally we try to find mode based on Accept-Language header // Must be made lowercase to be case insensitive. String wholeHeader = request.getHeader("Accept-Language"); if (wholeHeader == null) // Can happen with unusual browsers (or telnet, for that matter) wholeHeader = ""; else wholeHeader = wholeHeader.toLowerCase(); // Languages are separated by commas. Enumeration tokens = new StringTokenizer(wholeHeader, ","); // We may need multiple passes to process the base prefixes of languages // with dashes in them. List nextPass = null; do { while (tokens.hasMoreElements()) { String lang = (String)tokens.nextElement(); lang = lang.trim(); View theView = (View)modes.get(lang); if (theView != null) { log.debug("Using mode: " + lang); return theView; } int dash = lang.lastIndexOf("-"); if (dash >= 0) { // Make sure we create the list if (nextPass == null) nextPass = new ArrayList(); // Keep it for later! nextPass.add(lang.substring(0, dash)); } } // If there is more to process, use it as the token stream and start over. if (nextPass != null) { tokens = Collections.enumeration(nextPass); nextPass = null; } } while (tokens.hasMoreElements()); // Try the default view if nothing else was found View defaultView = (View)modes.get(null); if (defaultView != null) return defaultView; // Wow, after all that, we come up empty handed. throw new NoSuitableModeException("No appropriate mode could be found for Accepts-Language \"" + wholeHeader + "\". Possibilities were: " + modes.keySet()); } } /** * Logging category for log4j. */ private static Category log = Category.getInstance(LanguageShuntFactory.class.getName()); /** * Provides default language to web application. */ public void init(Element factoryNode, ServletConfig servletCfg) { this.defaultLanguage = XML.getValue(factoryNode, ATTR_DEFAULT_LANGUAGE); } /** * Merely creates a shunt object. */ public Shunt createShunt() throws ConfigException { log.debug("Creating language shunt"); return new LanguageShunt(); } }