Added method to retrieve the codes of a specific bundle.

For example if you want to send all client messages contained in
messagesclien bundle to the browser using i18next, you can now
retrieve all codes contained in the messagesclient bundle.

Author: tkvw

grails-core/src/main/groovy/org/grails/spring/context/support/ReloadableResourceBundleMessageSource.java

@@ -23,10 +23,7 @@
 import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.text.MessageFormat;
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Locale;
-import java.util.Properties;
+import java.util.*;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
@@ -153,6 +150,41 @@ public void setBasename(String basename) {
 		setBasenames(basename);
 	}
 
+	/**
+	 * Retrieves all codes from one or multiple basenames
+	 * @param locale the locale
+	 * @param basenames the basenames of the bundle
+	 * @return a list with all codes from valid registered bundles
+	 */
+	public List<String> getBundleCodes(Locale locale,String...basenames){
+		List<String> validBaseNames = getValidBasenames(basenames);
+		
+		List<String> codes = new ArrayList<>();
+		for(String basename: validBaseNames){
+			List<Pair<String, Resource>> filenamesAndResources = calculateAllFilenames(basename,locale);
+			for (Pair<String, Resource> filenameAndResource : filenamesAndResources) {
+				if(filenameAndResource.getbValue() != null) {
+					PropertiesHolder propHolder = getProperties(filenameAndResource.getaValue(), filenameAndResource.getbValue());
+					codes.addAll(propHolder.getProperties().stringPropertyNames());					
+				}
+			}
+		}
+		return codes;
+	}
+	
+	protected List<String> getValidBasenames(String[] basenames){
+		List<String> validBaseNames = new LinkedList<>();
+		for(String basename:basenames){
+			for(int i=0;i<this.basenames.length;i++){
+				if(basenames[i].equals(basename)){
+					validBaseNames.add(basename);
+					break;
+				}
+			}
+		}
+		return validBaseNames;
+	}
+	
 	/**
 	 * Set an array of basenames, each following the basic ResourceBundle convention
 	 * of not specifying file extension or language codes, but in contrast to