ADD:: Alert for taken username

build.gradle

@@ -18,9 +18,9 @@ apply plugin: 'org.springframework.boot'
 apply plugin: 'io.spring.dependency-management'
 apply plugin: 'application'
 
-application {
-    mainClassName = 'greenify.server.Application'
-}
+//application {
+//    mainClassName = 'greenify.server.Application'
+//}
 
 repositories {
     mavenCentral()

src/Client/src/main/java/greenify/client/controller/DashBoardController.java

@@ -422,7 +422,7 @@ public class DashBoardController {
     }
 
     /**
-     * method opend addFriend scene.
+     * method opens addFriend scene.
      * @throws IOException when file is not found
      */
     public void openAddFriend() throws IOException {

src/Client/src/main/java/greenify/client/controller/RegisterWindowController.java

@@ -2,6 +2,7 @@ package greenify.client.controller;
 
 import greenify.client.Application;
 import greenify.client.rest.UserService;
+import greenify.common.ApplicationException;
 import javafx.animation.Interpolator;
 import javafx.animation.KeyFrame;
 import javafx.animation.KeyValue;
@@ -228,7 +229,14 @@ public class RegisterWindowController {
         }
 
         //register the user with the provided username and password
-        userService.registerUser(userNameText.getText(), passwordField.getText());
+        try{
+            userService.registerUser(userNameText.getText(), passwordField.getText());
+        }
+        catch(RuntimeException ex){
+            UserController.AlertHelper.showAlert(Alert.AlertType.ERROR, owner, "Password Error!",
+                    "This username has already been taken!");
+            return;
+        }
         //close the register window after the user has entered all the credentials
         Stage current = (Stage) owner;
         current.close();