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 
5 private final UserRepository userRepository;
6 
7 public UserController(UserRepository userRepository) {
8 this.userRepository = userRepository;
9 }
10 
11 @GetMapping("/{id}")
12 public ResponseEntity<UserResponse> getUser(@PathVariable Long id) {
13 return userRepository.findById(id)
14 .map(this::toResponse)
15 .map(ResponseEntity::ok)
16 .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND, "User not found"));
17 }
18 
19 @GetMapping
20 public List<UserResponse> listUsers() {
21 return userRepository.findAll().stream()
22 .map(this::toResponse)
23 .toList();
24 }
25 
26 private UserResponse toResponse(User user) {
27 return new UserResponse(
28 user.getId(),
29 user.getFullName(),
30 user.getEmail(),
31 user.getRole().name(),
32 user.getCreatedAt()
33 );
34 }
35 
36 public record UserResponse(
37 Long id,
38 String fullName,
39 String email,
40 String role,
41 Instant createdAt
42 ) {}
43}
01 / 01
STEP 01

Walkthrough

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

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