[FIXED] How to handle Ambiguous handler methods mapped in REST application with Spring

Issue

In my UserController, I have 3 @GetMapping methods:

getAllUsers() - It is used to get all users, getUserById() - It is used to get specific user with his unique id and getUserByName() - It is used to get specific user with his unique name.

The code from the method is as follows:

@RestController
@RequestMapping("/users")
public class UserController {

    private final UserRepository userRepository;

    @Autowired
    public UserController(UserRepository userRepository) {
        this.userRepository = userRepository;
    }


    @GetMapping
    public List<User> getAllUsers() {
        return userRepository.findAll();
    }


    @GetMapping(value = "/{id}")
    public ResponseEntity<User> getUserById(@PathVariable Long id) {
        User user = userRepository.findById(id);
        return ResponseEntity.ok(user);
    }


    @GetMapping(value = "/{name}")
    public ResponseEntity<User> getUserByName(@PathVariable String name) {
        User user = userRepository.findUserByName(name);
        return ResponseEntity.ok(user);
    }

The first problem is that my app doesn't know if the URL is String or Integer, so I solved the problem between the getUserById() and getUserByName() methods like this:

    @GetMapping(value = "{id}")
    public ResponseEntity<User> getUserById(@PathVariable Long id) {
        User user = userRepository.findById(id);
        return ResponseEntity.ok(user);
    }


    @GetMapping
    public ResponseEntity<User> getUserByName(@RequestParam(value = "name") String name) {
        User user = userRepository.findUserByName(name);
        return ResponseEntity.ok(user);
    }

So now I can access the methods with:

http://localhost:8080/users/1 and http://localhost:8080/users?name=john

When I run the application, I get this error:

Caused by: java.lang.IllegalStateException: Ambiguous mapping. Cannot map 'userController' method 
com.db.userapp.controller.UserController#getUserByName(String)
to {GET [/users]}: There is already 'userController' bean method

I believe this is because my getAllUsers() and getUserByName() methods are on the same URL format. Does anyone have an idea how I can solve this?

Solution

You are right because both getAllUsers() and getUserByName() are mapped to the /users/. So for the request /users/ , it does not know which method should be used to process it.

You can configure the name query parameter for /users/ as optional and check if its value is null. Null means user does not want have any filtering on the users and want to get all users :

@RestController
@RequestMapping("/users")
public class UserController {

    @GetMapping
    public List<User> getUser(@RequestParam(value = "name",required = false) String name) {

        if (Strings.isNullOrEmpty(name)) {
            return userRepository.findAll();
        } else {
            return userRepository.findUserByName(name);
        }
    }
}

Answered By - Ken Chan
Answer Checked By - Willingham (JavaFixing Volunteer)