[SHIBUI-814]

Added an endpoint that retrieves a list of supported locales.

backend/src/main/java/edu/internet2/tier/shibboleth/admin/ui/controller/InternationalizationMessagesController.java

@@ -7,7 +7,13 @@
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RequestMapping;
 
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.Locale;
+import java.util.MissingResourceException;
+import java.util.ResourceBundle;
+import java.util.Set;
+import java.util.stream.Collectors;
 
 /**
  * @author Bill Smith (wsmith@unicon.net)
@@ -22,4 +28,33 @@ public class InternationalizationMessagesController {
     public ResponseEntity<?> getAll(Locale locale) {
         return ResponseEntity.ok(messageSource.getMessagesMap(locale));
     }
+
+    @GetMapping(value = "/available")
+    public ResponseEntity<?> getAvailableLocales() {
+        Set<ResourceBundle> supportedLocaleResourceBundles = getResourceBundles();
+        Set<Locale> supportedLocales = supportedLocaleResourceBundles
+                .stream()
+                .map(ResourceBundle::getLocale)
+                .collect(Collectors.toSet());
+        return ResponseEntity.ok(supportedLocales);
+    }
+
+    /**
+     * Get all available resource bundles in i18n/messages that matches a locale supported by this JRE.
+     *
+     * @return a set of resource bundles for supported locales for this system
+     */
+    private Set<ResourceBundle> getResourceBundles() {
+        Set<ResourceBundle> resourceBundles = new HashSet<>();
+
+        for (Locale locale : Locale.getAvailableLocales()) {
+            try {
+                resourceBundles.add(ResourceBundle.getBundle("i18n/messages", locale));
+            } catch (MissingResourceException e) {
+                // do nothing
+            }
+        }
+
+        return Collections.unmodifiableSet(resourceBundles);
+    }
 }