java 43 lines · 7 steps

How a Spring REST controller maps users

A Spring controller exposes read endpoints that fetch users and convert entities into a clean response record.

Explained by highlit

Spring Intermediate rest-api dependency-injection dto-mapping optional records

1@RestController
2@RequestMapping("/api/users")
3public class UserController {
4 
  private final UserRepository userRepository;
6 
  public UserController(UserRepository userRepository) {
      this.userRepository = userRepository;
  }
10 
  @GetMapping("/{id}")
  public ResponseEntity<UserResponse> getUser(@PathVariable Long id) {
      return userRepository.findById(id)
              .map(this::toResponse)
              .map(ResponseEntity::ok)
              .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND, "User not found"));
  }
18 
  @GetMapping
  public List<UserResponse> listUsers() {
      return userRepository.findAll().stream()
              .map(this::toResponse)
              .toList();
  }
25 
  private UserResponse toResponse(User user) {
      return new UserResponse(
              user.getId(),
              user.getFullName(),
              user.getEmail(),
              user.getRole().name(),
              user.getCreatedAt()
      );
  }
35 
  public record UserResponse(
          Long id,
          String fullName,
          String email,
          String role,
          Instant createdAt
  ) {}
43}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Mapping entities to a dedicated response type keeps your API contract decoupled from your database schema.
2Chaining Optional's map and orElseThrow turns a missing lookup into a clean HTTP error without null checks.
3Constructor injection of a repository makes controllers easy to test and their dependencies explicit.

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