Consider defining a bean of type 'UserConverter' in your configuration

I don't know what happend with my spring boot application but now I can't to start it because of an error:

***************************
APPLICATION FAILED TO START
***************************
Description:
Field userConverter in webapp.controllers.UserResourceController required a bean of type 'webapp.converter.UserConverter' that could not be found.
The injection point has the following annotations:
	- @org.springframework.beans.factory.annotation.Autowired(required=true)
Action:
Consider defining a bean of type 'webapp.converter.UserConverter' in your configuration.
Process finished with exit code 1

Controller code:

@RestController
@RequestMapping("/api/user")
public class UserResourceController {

@Autowired
private UserServiceImpl userService;

@Autowired
private UserConverter userConverter;

@PostMapping
public ResponseEntity<UserDto> addUser(@RequestBody UserDto userDto) {
    userService.persist(userConverter.toUser(userDto));
    return ResponseEntity.ok().body(userDto);
}

@GetMapping
public ResponseEntity<List<UserDto>> findAllUsers() {
    return ResponseEntity.ok(userConverter.toUserDtos(userService.getAll()));
}

@PutMapping("/api/user/{id}")
public ResponseEntity<UserDto> updateUser(@PathVariable Long id, @RequestBody UserDto userDto) {
    User user = userConverter.toUser(userDto);
    user.setId(id);
    userService.persist(user);
    return ResponseEntity.ok().body(userDto);
}

@GetMapping("/api/user/{id}")
public ResponseEntity<UserDto> findUser (@PathVariable Long id) {
    Optional<User> user = Optional.ofNullable(userService.getByKey(id));
    return ResponseEntity.ok(userConverter.toUserDto(user.get()));
}
}

The mapper class:

@Mapper(componentModel = "spring")
@Service
public abstract class UserConverter {
    public abstract User toUser(UserDto userDto);
    public abstract UserDto toUserDto(User user);
    public abstract List<UserDto> toUserDtos(List<User> users);
}

The first I tried to run it without @Service annotation, and then with it annotation but I always see the same error.

You couldn't inject an abstract class which doesn't have any real implementation. It isn't possible in Java even without Spring. So have do you expect it could be injected?

I don't understand why do you need to inject that class. The best solution will create a utility class with the appropriate converter, like:

public final class UserConverter {
    private UserConverter() {}

    public static UserDTO toUserDTO(User employee) {
        Department empDp = employee.getDepartment();
        return UserDTO.builder()
                .id(employee.getId())
                .name(employee.getName())
                .active(employee.getActive())
                .departmentId(empDp.getId())
                .departmentName(empDp.getName())
                .build();
    }

    public static User toUser(UserDTO dto) {
        Department dp = Department.builder()
                .id(dto.getDepartmentId())
                .name(dto.getDepartmentName())
                .build();
        return User.builder()
                .id(dto.getId())
                .name(dto.getName())
                .active(dto.getActive())
                .department(dp)
                .build();
    }
}

And call it as a static method from your code:

@GetMapping("/{id}")
public ResponseEntity<UserDto> findUser (@PathVariable Long id) {
    return userService.getByKey(id)
            .map(ResponseEntity::ok)
            .orElse(ResponseEntity.notFound().build());
}

Also, your code has some mistakes for your API:

• mapping to resource should be plural like @RequestMapping("/api/users") -> and only when you need operation by id add @GetMapping("/{id}")

• create method should return 201 - Create status code instead of 200

• if /api should be common for all your API you could define it at the configuration file for all your resources.
  Snippet from applicatoin.yml:

  server:
  servlet:
  context-path: /api

Useful references for solutions with MapStruct:

• Quick Guide to MapStruct
• Automating Code with MapStruct