ResponseEntity<?> vs Strongly Typed ResponseEntity

1. Can ResponseEntity<?> Handle Both Success and Error Responses?

Yes.

ResponseEntity<?> can accept:

Success DTO
Error DTO
String
Map
Any Java object

because:

?

means:

unknown generic type

Example

@GetMapping("/{id}")
public ResponseEntity<?> getUser(@PathVariable Long id) {

    User user = service.find(id);

    if (user == null) {

        return ResponseEntity
                .status(HttpStatus.NOT_FOUND)
                .body(Map.of(
                        "message", "User not found"
                ));
    }

    return ResponseEntity.ok(
            new UserResponse(user)
    );
}

This works completely fine.

2. Why Enterprises Usually Avoid ResponseEntity<?> in Controllers

Although valid, enterprise systems usually avoid:

ResponseEntity<?>

for standard business APIs.

Problems with ResponseEntity<?>

1. Weak Type of Safety

Compiler cannot guarantee response type.

2. Poor API Readability

This:

ResponseEntity<?>

does NOT clearly communicate:

What does this API return?

3. Swagger / OpenAPI Issues

API documentation becomes unclear.

Generated schema may become:

generic
ambiguous
inconsistent

4. Mixed Response Contracts

Controller starts handling:

success flow
validation flow
business errors
exception handling

inside the same method.

This leads to:

fat controllers

3. Industry Recommended Approach

Use Strongly Typed Responses

Prefer:

ResponseEntity<UserResponse>

instead of:

ResponseEntity<?>

Example

@GetMapping("/{id}")
public ResponseEntity<UserResponse> getUser(
        @PathVariable Long id) {

    return ResponseEntity.ok(
            service.get(id)
    );
}

4. How Errors Are Handled in Real Enterprise Systems

Instead of:

if (user == null)

controllers usually:

throw exceptions

and let:

@RestControllerAdvice

handle them globally.

5. Recommended Enterprise Architecture

Controller

@GetMapping("/{id}")
public ResponseEntity<UserResponse> getUser(
        @PathVariable Long id) {

    return ResponseEntity.ok(
            service.get(id)
    );
}

Service Layer

public UserResponse get(Long id) {

    User user = repository.findById(id)
            .orElseThrow(() ->
                    new UserNotFoundException(id));

    return mapper.toResponse(user);
}

Global Exception Handler

@RestControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(UserNotFoundException.class)
    public ResponseEntity<ErrorResponse> handle(
            UserNotFoundException ex) {

        ErrorResponse error =
                new ErrorResponse(
                        "USER_NOT_FOUND",
                        ex.getMessage()
                );

        return ResponseEntity
                .status(HttpStatus.NOT_FOUND)
                .body(error);
    }
}

6. Why This Design Is Better

Controllers Stay Clean

Controller only handles:

request
delegation
success response

Clean Controller Example

return ResponseEntity.ok(service.get(id));

instead of:

if / else / try / catch

Strong Typing

ResponseEntity<UserResponse>

provides:

compile-time safety
better readability
better IDE support
better OpenAPI docs

Centralized Error Handling

All error responses become:

standardized
reusable
maintainable

7. When ResponseEntity<?> Is Still Commonly Used

There are valid use cases.

Scenario	Usage
Gateway APIs	common
Proxy services	common
Generic utility APIs	common
Framework-level code	common
Dynamic response structures	common

8. Senior Engineering Insight

The cleanest production-grade controllers usually look like this:

@GetMapping("/{id}")
public ResponseEntity<UserResponse> get(
        @PathVariable Long id) {

    return ResponseEntity.ok(
            service.get(id)
    );
}

No:

try/catch
if/else error handling
mixed response types

Errors are handled separately via:

@RestControllerAdvice

This separation of concerns is considered:

production-grade REST architecture

9. Industry Recommendation Summary

Preferred

ResponseEntity<SuccessDTO>

with:

global exception handling
standardized error responses

Avoid Excessive Use Of

ResponseEntity<?>

inside normal business controllers.

10. Final Takeaway

Good Enterprise Controllers Should:

✅ return strongly typed DTOs
✅ delegate error handling globally
✅ remain thin and predictable
✅ separate success and failure concerns

Recommended Flow

Controller
    ↓
Service
    ↓
Success DTO Response

Exceptions
    ↓
@ControllerAdvice
    ↓
Standard Error Response