refactor: throw proper error on registration conflict, handle properly

backend/src/main/java/de/szut/casino/exceptionHandling/GlobalExceptionHandler.java

@@ -2,6 +2,7 @@ package de.szut.casino.exceptionHandling;
 
 import de.szut.casino.exceptionHandling.exceptions.InsufficientFundsException;
 import de.szut.casino.exceptionHandling.exceptions.UserNotFoundException;
+import jakarta.persistence.EntityExistsException;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.ControllerAdvice;
@@ -24,4 +25,10 @@ public class GlobalExceptionHandler {
         ErrorDetails errorDetails = new ErrorDetails(new Date(), ex.getMessage(), request.getDescription(false));
         return new ResponseEntity<>(errorDetails, HttpStatus.BAD_REQUEST);
     }
+
+    @ExceptionHandler(EntityExistsException.class)
+    public ResponseEntity<?> handleEntityExistsException(EntityExistsException ex, WebRequest request) {
+        ErrorDetails errorDetails = new ErrorDetails(new Date(), ex.getMessage(), request.getDescription(false));
+        return new ResponseEntity<>(errorDetails, HttpStatus.CONFLICT);
+    }
 }

backend/src/main/java/de/szut/casino/user/UserService.java

@@ -1,6 +1,7 @@
 package de.szut.casino.user;
 
 import de.szut.casino.user.dto.CreateUserDto;
+import jakarta.persistence.EntityExistsException;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.security.core.context.SecurityContextHolder;
 import org.springframework.security.crypto.password.PasswordEncoder;
@@ -19,11 +20,11 @@ public class UserService {
 
     public UserEntity createUser(CreateUserDto createUserDto) {
         if (userRepository.existsByUsername(createUserDto.getUsername())) {
-            throw new IllegalArgumentException("Username is already taken");
+            throw new EntityExistsException("Username is already taken");
         }
 
         if (userRepository.existsByEmail(createUserDto.getEmail())) {
-            throw new IllegalArgumentException("Email is already in use");
+            throw new EntityExistsException("Email is already in use");
         }
         
         UserEntity user = new UserEntity(

frontend/src/app/feature/auth/register/register.component.html

@@ -2,9 +2,11 @@
   <div class="modal-card max-w-md w-full">
     <h2 class="modal-heading text-center">Konto erstellen</h2>
 
-    <div *ngIf="errorMessage" class="bg-accent-red text-white p-4 rounded mb-4">
+    @if (errorMessage()) {
-      {{ errorMessage }}
+      <div class="bg-accent-red text-white p-4 rounded mb-4">
-    </div>
+        {{ errorMessage() }}
+      </div>
+    }
 
     <form [formGroup]="registerForm" (ngSubmit)="onSubmit()" class="space-y-4">
       <div>
@@ -14,18 +16,26 @@
           type="email"
           formControlName="email"
           class="w-full px-4 py-2.5 bg-deep-blue-light/50 text-white rounded-lg my-1 border border-deep-blue-light/30 focus:border-emerald/50 focus:ring-1 focus:ring-emerald/50 outline-none transition-all duration-200"
+          [ngClass]="{ 'border-accent-red': fieldErrors()['email'] }"
           placeholder="Gib deine E-Mail-Adresse ein"
         />
 
-        <div
+        @if (fieldErrors()['email']) {
-          *ngIf="form['email'].touched && form['email'].errors"
+          <div class="text-accent-red mt-1 text-sm">
-          class="text-accent-red mt-1 text-sm"
+            {{ fieldErrors()['email'] }}
-        >
+          </div>
-          <span *ngIf="form['email'].errors?.['required']">E-Mail ist erforderlich</span>
+        }
-          <span *ngIf="form['email'].errors?.['email']">
+
-            Bitte gib eine gültige E-Mail-Adresse ein
+        @if (!fieldErrors()['email'] && form['email'].touched && form['email'].errors) {
-          </span>
+          <div class="text-accent-red mt-1 text-sm">
-        </div>
+            @if (form['email'].errors['required']) {
+              <span>E-Mail ist erforderlich</span>
+            }
+            @if (form['email'].errors['email']) {
+              <span>Bitte gib eine gültige E-Mail-Adresse ein</span>
+            }
+          </div>
+        }
       </div>
 
       <div>
@@ -37,18 +47,26 @@
           type="text"
           formControlName="username"
           class="w-full px-4 py-2.5 bg-deep-blue-light/50 text-white rounded-lg my-1 border border-deep-blue-light/30 focus:border-emerald/50 focus:ring-1 focus:ring-emerald/50 outline-none transition-all duration-200"
+          [ngClass]="{ 'border-accent-red': fieldErrors()['username'] }"
           placeholder="Wähle einen Benutzernamen"
         />
 
-        <div
+        @if (fieldErrors()['username']) {
-          *ngIf="form['username'].touched && form['username'].errors"
+          <div class="text-accent-red mt-1 text-sm">
-          class="text-accent-red mt-1 text-sm"
+            {{ fieldErrors()['username'] }}
-        >
+          </div>
-          <span *ngIf="form['username'].errors?.['required']">Benutzername ist erforderlich</span>
+        }
-          <span *ngIf="form['username'].errors?.['minlength']">
+
-            Benutzername muss mindestens 3 Zeichen haben
+        @if (!fieldErrors()['username'] && form['username'].touched && form['username'].errors) {
-          </span>
+          <div class="text-accent-red mt-1 text-sm">
-        </div>
+            @if (form['username'].errors['required']) {
+              <span>Benutzername ist erforderlich</span>
+            }
+            @if (form['username'].errors['minlength']) {
+              <span>Benutzername muss mindestens 3 Zeichen haben</span>
+            }
+          </div>
+        }
       </div>
 
       <div>
@@ -63,24 +81,25 @@
           placeholder="Erstelle ein Passwort"
         />
 
-        <div
+        @if (form['password'].touched && form['password'].errors) {
-          *ngIf="form['password'].touched && form['password'].errors"
+          <div class="text-accent-red mt-1 text-sm">
-          class="text-accent-red mt-1 text-sm"
+            @if (form['password'].errors['required']) {
-        >
+              <span>Passwort ist erforderlich</span>
-          <span *ngIf="form['password'].errors?.['required']">Passwort ist erforderlich</span>
+            }
-          <span *ngIf="form['password'].errors?.['minlength']">
+            @if (form['password'].errors['minlength']) {
-            Passwort muss mindestens 6 Zeichen haben
+              <span>Passwort muss mindestens 6 Zeichen haben</span>
-          </span>
+            }
-        </div>
+          </div>
+        }
       </div>
 
       <div class="pt-2">
         <button
           type="submit"
-          [disabled]="registerForm.invalid || isLoading"
+          [disabled]="registerForm.invalid || isLoading()"
           class="button-primary w-full py-2.5 rounded"
         >
-          {{ isLoading ? 'Konto wird erstellt...' : 'Registrieren' }}
+          {{ isLoading() ? 'Konto wird erstellt...' : 'Registrieren' }}
         </button>
       </div>
     </form>

frontend/src/app/feature/auth/register/register.component.ts

@@ -1,9 +1,10 @@
-import { Component } from '@angular/core';
+import { Component, signal } from '@angular/core';
 import { FormBuilder, FormGroup, ReactiveFormsModule, Validators } from '@angular/forms';
 import { Router, RouterLink } from '@angular/router';
 import { RegisterRequest } from '../../../model/auth/RegisterRequest';
 import { AuthService } from '@service/auth.service';
 import { CommonModule } from '@angular/common';
+import { HttpErrorResponse } from '@angular/common/http';
 
 @Component({
   selector: 'app-register',
@@ -13,8 +14,9 @@ import { CommonModule } from '@angular/common';
 })
 export class RegisterComponent {
   registerForm: FormGroup;
-  errorMessage = '';
+  errorMessage = signal<string>('');
-  isLoading = false;
+  isLoading = signal<boolean>(false);
+  fieldErrors = signal<{ [key: string]: string }>({});
 
   constructor(
     private fb: FormBuilder,
@@ -37,8 +39,9 @@ export class RegisterComponent {
       return;
     }
 
-    this.isLoading = true;
+    this.isLoading.set(true);
-    this.errorMessage = '';
+    this.errorMessage.set('');
+    this.fieldErrors.set({});
 
     const registerRequest: RegisterRequest = {
       email: this.form['email'].value,
@@ -59,15 +62,33 @@ export class RegisterComponent {
               this.router.navigate(['/home']);
             },
             error: () => {
-              this.isLoading = false;
+              this.isLoading.set(false);
-              this.errorMessage =
+              this.errorMessage.set(
-                'Registration successful but failed to login automatically. Please log in manually.';
+                'Registration successful but failed to login automatically. Please log in manually.'
+              );
             },
           });
       },
-      error: (err) => {
+      error: (err: HttpErrorResponse) => {
-        this.isLoading = false;
+        this.isLoading.set(false);
-        this.errorMessage = err.error?.message || 'Failed to register. Please try again.';
+
+        if (err.status === 409) {
+          const errorResponse = err.error;
+
+          if (errorResponse?.message === 'Email is already in use') {
+            this.fieldErrors.update((errors) => ({
+              ...errors,
+              email: 'Diese E-Mail-Adresse wird bereits verwendet.',
+            }));
+          } else if (errorResponse?.message === 'Username is already taken') {
+            this.fieldErrors.update((errors) => ({
+              ...errors,
+              username: 'Dieser Benutzername ist bereits vergeben.',
+            }));
+          }
+        } else {
+          this.errorMessage.set(err.error?.message || 'Failed to register. Please try again.');
+        }
       },
     });
   }