update

src/main/java/com/devteria/identityservice/controller/UserController.java

 package com.devteria.identityservice.controller;
 
+import com.devteria.identityservice.dto.request.ApiResponse;
 import com.devteria.identityservice.dto.request.UserCreationRequest;
 import com.devteria.identityservice.dto.request.UserUpdateRequest;
 import com.devteria.identityservice.entity.User;
@@ -17,8 +18,12 @@ public class UserController {
     private UserService userService;
 
     @PostMapping
-    User createUser(@RequestBody @Valid UserCreationRequest request){
-        return userService.createUser(request);
+    ApiResponse<User> createUser(@RequestBody @Valid UserCreationRequest request){
+        ApiResponse<User> apiResponse = new ApiResponse<>();
+
+        apiResponse.setResult(userService.createUser(request));
+
+        return apiResponse;
     }
 
     @GetMapping

src/main/java/com/devteria/identityservice/dto/request/ApiResponse.java

+package com.devteria.identityservice.dto.request;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+
+@JsonInclude(JsonInclude.Include.NON_NULL)
+public class ApiResponse <T> {
+    private int code = 1000;
+    private String message;
+    private T result;
+
+    public int getCode() {
+        return code;
+    }
+
+    public void setCode(int code) {
+        this.code = code;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+
+    public void setMessage(String message) {
+        this.message = message;
+    }
+
+    public T getResult() {
+        return result;
+    }
+
+    public void setResult(T result) {
+        this.result = result;
+    }
+}

src/main/java/com/devteria/identityservice/dto/request/UserCreationRequest.java

@@ -5,10 +5,10 @@ import jakarta.validation.constraints.Size;
 import java.time.LocalDate;
 
 public class UserCreationRequest {
-    @Size(min = 3,message = "Username must be at least 3 characters")
+    @Size(min = 3,message = "USERNAME_INVALID")
     private String username;
 
-    @Size(min = 8, message = "Password must be at least 8 characters")
+    @Size(min = 8, message = "INVALID_PASSWORD")
     private String password;
     private String firstName;
     private String lastName;

src/main/java/com/devteria/identityservice/exception/AppException.java

+package com.devteria.identityservice.exception;
+
+public class AppException extends RuntimeException{
+
+    public AppException(ErrorCode errorCode) {
+        super(errorCode.getMessage());
+        this.errorCode = errorCode;
+    }
+
+    private ErrorCode errorCode;
+
+    public ErrorCode getErrorCode() {
+        return errorCode;
+    }
+
+    public void setErrorCode(ErrorCode errorCode) {
+        this.errorCode = errorCode;
+    }
+}

src/main/java/com/devteria/identityservice/exception/ErrorCode.java

+package com.devteria.identityservice.exception;
+
+public enum ErrorCode {
+    UNCATEGORIZED_EXCEPTION(9999, "Uncategorized error"),
+    INVALID_KEY(1001, "Uncategorized error"),
+    USER_EXISTED(1002, "User existed"),
+    USERNAME_INVALID(1003, "Username must be at least 3 characters"),
+    INVALID_PASSWORD(1004, "Password must be at least 8 characters")
+    ;
+
+    ErrorCode(int code, String message) {
+        this.code = code;
+        this.message = message;
+    }
+
+    private int code;
+    private String message;
+
+    public int getCode() {
+        return code;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+}

src/main/java/com/devteria/identityservice/exception/GlobalExceptionHandler.java

 package com.devteria.identityservice.exception;
 
+import com.devteria.identityservice.dto.request.ApiResponse;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.MethodArgumentNotValidException;
 import org.springframework.web.bind.annotation.ControllerAdvice;
@@ -8,13 +9,44 @@ import org.springframework.web.bind.annotation.ExceptionHandler;
 @ControllerAdvice
 public class GlobalExceptionHandler {
 
-    @ExceptionHandler(value = RuntimeException.class)
-    ResponseEntity<String> handlingRuntimeException(RuntimeException exception){
-        return ResponseEntity.badRequest().body(exception.getMessage());
+    @ExceptionHandler(value = Exception.class)
+    ResponseEntity<ApiResponse> handlingRuntimeException(RuntimeException exception){
+        ApiResponse apiResponse = new ApiResponse();
+
+        apiResponse.setCode(ErrorCode.UNCATEGORIZED_EXCEPTION.getCode());
+        apiResponse.setMessage(ErrorCode.UNCATEGORIZED_EXCEPTION.getMessage());
+
+        return ResponseEntity.badRequest().body(apiResponse);
+    }
+
+    @ExceptionHandler(value = AppException.class)
+    ResponseEntity<ApiResponse> handlingAppException(AppException exception){
+        ErrorCode errorCode = exception.getErrorCode();
+        ApiResponse apiResponse = new ApiResponse();
+
+        apiResponse.setCode(errorCode.getCode());
+        apiResponse.setMessage(errorCode.getMessage());
+
+        return ResponseEntity.badRequest().body(apiResponse);
     }
 
     @ExceptionHandler(value = MethodArgumentNotValidException.class)
-    ResponseEntity<String> handlingValidation(MethodArgumentNotValidException exception){
-        return ResponseEntity.badRequest().body(exception.getFieldError().getDefaultMessage());
+    ResponseEntity<ApiResponse> handlingValidation(MethodArgumentNotValidException exception){
+        String enumKey = exception.getFieldError().getDefaultMessage();
+
+        ErrorCode errorCode = ErrorCode.INVALID_KEY;
+
+        try {
+            errorCode = ErrorCode.valueOf(enumKey);
+        } catch (IllegalArgumentException e){
+
+        }
+
+        ApiResponse apiResponse = new ApiResponse();
+
+        apiResponse.setCode(errorCode.getCode());
+        apiResponse.setMessage(errorCode.getMessage());
+
+        return ResponseEntity.badRequest().body(apiResponse);
     }
 }

src/main/java/com/devteria/identityservice/service/UserService.java

@@ -3,6 +3,8 @@ package com.devteria.identityservice.service;
 import com.devteria.identityservice.dto.request.UserCreationRequest;
 import com.devteria.identityservice.dto.request.UserUpdateRequest;
 import com.devteria.identityservice.entity.User;
+import com.devteria.identityservice.exception.AppException;
+import com.devteria.identityservice.exception.ErrorCode;
 import com.devteria.identityservice.repository.UserRepository;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Service;
@@ -18,7 +20,7 @@ public class UserService {
         User user = new User();
 
         if (userRepository.existsByUsername(request.getUsername()))
-            throw new RuntimeException("User existed.");
+            throw new AppException(ErrorCode.USER_EXISTED);
 
         user.setUsername(request.getUsername());
         user.setPassword(request.getPassword());