feat : 이메일 중복 체크 추가

backend/src/main/java/com/edufocus/edufocus/user/controller/UserController.java

@@ -37,6 +37,9 @@ public class UserController {
         if(userService.isUserIdExist(requestJoinDto.getUserId()))
             return new ResponseEntity<>("아이디가 중복 됐습니다.", HttpStatus.CONFLICT);
 
+        if(userService.isEmailExist(requestJoinDto.getEmail()))
+            return new ResponseEntity<>("이메일이 중복 됐습니다.", HttpStatus.CONFLICT);
+
         userService.join(requestJoinDto);
 
         return ResponseEntity.ok("User registered successfully");

backend/src/main/java/com/edufocus/edufocus/user/model/repository/UserRepository.java

@@ -31,4 +31,5 @@ public interface UserRepository extends JpaRepository<User,Long> {
 
     Optional<User> findByUserId(String userId);
 
+    Optional<User> findByEmail(String email);
 }

backend/src/main/java/com/edufocus/edufocus/user/model/service/UserService.java

@@ -25,4 +25,6 @@ public interface UserService {
         void changePassword(PasswordDto passwordDto,Long id);
 
         boolean isUserIdExist(String userId);
+
+        boolean isEmailExist(String email);
 }

backend/src/main/java/com/edufocus/edufocus/user/model/service/UserServiceImpl.java

@@ -113,6 +113,11 @@ public class UserServiceImpl implements UserService {
         return userRepository.findByUserId(userId).isPresent();
     }
 
+    @Override
+    public boolean isEmailExist(String email) {
+        return userRepository.findByEmail(email).isPresent();
+    }
+
     public String getTempPassword() {
         char[] charSet = new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F',
                 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'};