#1 Complete the REST controller

Objective: Assess a candidate’s practical experience and knowledge

Instructions: Given the below controller, fill in Spring annotations according to instructions given in the code comments

Pay attention to:

• Did the candidate notice the repetition of /friends prefix? Did he/she suggest a @RequestMapping(/friends) on the controller class instead?
• How did he/she annotate the optional parameter name and id in findFriends(String name, Long id) method?
• What annotation can be used to force a 204 (no content) response?

/* Assume all package, imports and dependency classes are available */

/**
 * A rest controller for Friend-related operations
 */
public class FriendController {
    private final FriendService friendService;

    public FriendController(FriendService friendService) {
        this.friendService = friendService;
    }

    /**
     * Response to GET /friends/ request
     * @param name (optional) filter by name
     * @param id (optional) filter by id
     * @return a list of friends
     */
    public List<FriendDTO> findFriends(String name, Long id) {
        if (id != null) {
            return friendService.findByFriendId(id);
        } else if (StringUtils.hasText(name)) {
            return friendService.findByName(name);
        } else {
            return friendService.findAll();
        }
    }

    /**
     * Response to GET /friends/hello/{friend's name} request
     * @param friend a friend's name
     * @return a friendly Hello
     */
    public String hello(String friend) {
        return String.format("Hello %s", friend);
    }

    /**
     * Response to POST /friends/hello/{friend's name} request
     * @param friend a friend's name which is to be saved
     * @return a friendly Hello together with Id of the new friend
     */
    public String helloAndSave(String friend) {
        FriendDTO dto = friendService.add(FriendDTO.builder().name(friend).createDt(LocalDateTime.now()).build());
        return String.format("%s. Your Id is %d", hello(friend), dto.getId());
    }

    /**
     * Un-friend
     * Response to DELETE /friends/{friend's id} request, 
     * return 204 if successful
     * @param friendId the id of the friend
     */
    public void deleteFriend(long friendId) {
        friendService.removeFriend(friendId);
    }

    /**
     * Update friend name
     * Response to <METHOD?> /friends/{friend's id}/{new name} request, 
     * return update friend info
     * @param friendId the id of the friend
     * @param newName the new name of the friend
     * @return updated friend's info
     */
    public FriendDTO updateFriend(long friendId, String newName) {
        return friendService.updateName(friendId, newName);
    }
}

#2 Write tests for controller

Objective: Assess a candidate’s practical experience and knowledge

Instructions: As devising test scenarios and writing them can be time-consuming, it is perhaps best to go through the solution verbally

Pay attention to:

• Did the candidate use (or at least mention) any popular test libraries such as JUNIT, Mockito, Hamcrest, Spring Boot Test?
• Which approach did the candidate take:
  a) Directly call controller method: controller.hello("world) . Did the candidate creates the controller instance with var controller = new FriendController(mockFriendService); or use the Mockito’s @InjectMockannotation to create the controller instance with dependencies auto-injected?
  b) Use a test runner (e.g. SpringRunner) and write integration-level test codes (e.g. webmvc.perform(...).andExpect(...) )
• How did the candidate organize the testing codes? Unorganized or Arrange...Act...Assert or Given...When...Then

#3 Handle error

Objective: Assess a candidate’s knowledge of HTTP status code, awareness of information disclosure, and exception handling

Questions & Hints:

1. How do you respond to a search for a non-existent resource?
   An empty list _[]_ is a fine response to a search query
2. How do you respond to a GET /friends/123 when there is no record with id 123?
   It should be a 404 response
3. How do you respond to a GET /friends/?id=some-name?
   It should be 400 — Bad Request because _some-name_ isn’t a _Long_
4. What do you need to do to return 400 in question 3?
   Spring automatically detects that the supplied parameter value _"some-name”_ cannot be cast to the declared _Long id_ method parameter and returns 400. The control never reaches the controller’s code
5. How do you map an application exception to a particular HTTP status code?
   It could be a custom exception annotated with _@RequestStatus(status = HttpStatus.XYZ)__
   Or apply the__@ExceptionHandler_ on a controller’s method to handle thrown exception
   Or implement an _@ControllerAdvice_ global handler
6. What HTTP status codes indicate successful execution?
   HTTP status in 200 range, most commonly 200, 201, 202 and 204
7. When do we use these statuses?
   200 — OK
   201 — Created
   202 — Accepted
   204 — No Content
8. What do you need to do to return 202 response?
   Either _@ResponseStatus_Or returning a _ResponseEntity.status(HttpStatus.CREATED)_

Extra: https://geraldnguyen.medium.com/list/api-development-interview-a17c1f9ee5b7: My articles related to API development and interview