cursor-rules-java

```java
/**
 * A REST controller for managing user profiles in a Spring Boot application.
 * Implements CRUD operations with validation and proper error handling.
 */
@RestController
@RequestMapping("/api/users")
@RequiredArgsConstructor
public class UserProfileController {

    private final UserService userService;
    private final UserMapper userMapper;

    @GetMapping("/{id}")
    public ResponseEntity<UserDTO> getUser(@PathVariable Long id) {
        User user = userService.findById(id)
            .orElseThrow(() -> new ResourceNotFoundException("User not found with id: " + id));
        return ResponseEntity.ok(userMapper.toDto(user));
    }

    @PostMapping
    public ResponseEntity<UserDTO> createUser(@Valid @RequestBody UserCreateRequest request) {
        User user = userMapper.toEntity(request);
        User savedUser = userService.save(user);
        return new ResponseEntity<>(userMapper.toDto(savedUser), HttpStatus.CREATED);
    }

    @PutMapping("/{id}")
    public ResponseEntity<UserDTO> updateUser(
            @PathVariable Long id,
            @Valid @RequestBody UserUpdateRequest request) {
        User existingUser = userService.findById(id)
            .orElseThrow(() -> new ResourceNotFoundException("User not found with id: " + id));
        userMapper.updateEntityFromDto(request, existingUser);
        User updatedUser = userService.save(existingUser);
        return ResponseEntity.ok(userMapper.toDto(updatedUser));
    }

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteUser(@PathVariable Long id) {
        userService.deleteById(id);
        return ResponseEntity.noContent().build();
    }
}

```

```java
/**
 * Unit tests for UserProfileController using JUnit 5 and Mockito.
 * Tests cover happy paths, validation, and error scenarios.
 */
@ExtendWith(MockitoExtension.class)
@WebMvcTest(UserProfileController.class)
class UserProfileControllerTest {

    @Autowired
    private MockMvc mockMvc;

    @MockBean
    private UserService userService;

    @MockBean
    private UserMapper userMapper;

    @Test
    void getUser_shouldReturnUserWhenExists() throws Exception {
        // Given
        Long userId = 1L;
        User user = new User(userId, "[email protected]", "password123", "Test User");
        UserDTO userDTO = new UserDTO(userId, "[email protected]", "Test User");

        given(userService.findById(userId)).willReturn(Optional.of(user));
        given(userMapper.toDto(user)).willReturn(userDTO);

        // When & Then
        mockMvc.perform(get("/api/users/{id}", userId))
            .andExpect(status().isOk())
            .andExpect(jsonPath("$.id").value(userId))
            .andExpect(jsonPath("$.email").value("[email protected]"));
    }

    @Test
    void createUser_shouldReturnCreatedUser() throws Exception {
        // Given
        UserCreateRequest request = new UserCreateRequest("[email protected]", "password123", "New User");
        User user = new User(2L, "[email protected]", "password123", "New User");
        UserDTO userDTO = new UserDTO(2L, "[email protected]", "New User");

        given(userMapper.toEntity(request)).willReturn(user);
        given(userService.save(user)).willReturn(user);
        given(userMapper.toDto(user)).willReturn(userDTO);

        // When & Then
        mockMvc.perform(post("/api/users")
                .contentType(MediaType.APPLICATION_JSON)
                .content(asJsonString(request)))
            .andExpect(status().isCreated())
            .andExpect(jsonPath("$.id").value(2L));
    }

    private static String asJsonString(final Object obj) {
        try {
            return new ObjectMapper().writeValueAsString(obj);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}
```