No access to public method in interface implementation class (access only to method declarated in interface)

Question

I have an interface and two implementations of this interface.

1. EmailTokenServiceImpl
2. ResetPasswordTokenServiceImpl

Interface contains only one method named generateToken()

In one of my implementation class ResetPasswordTokenServiceImpl I have added one more method named exampleMethod() .

Now the problem is when I autowired the service having extra method in my controller class I'm not able to call the exampleMethod()

Interface Declaration:

    public interface TokenService {

    /**
     * Generate verification token for given user.
     *
     * @param user the user entity
     * @return the verification token
     */
    public VerificationToken generateToken(User user);
    }

First Service:

    @Service(value = "emailTokenService")
    public class EmailTokenServiceImpl implements TokenService {

    @Value("${email.token.expiration.hours}")
    private int expirationIn;

    /**
     * Generate Token for email verification {@link EmailVerificationToken}
     * @return VerificationToken token
     */
    @Override
    public EmailVerificationToken generateToken(User user) {
        EmailVerificationToken token = new EmailVerificationToken();
        token.setToken(generateHash());
        token.setExpirationDate(getExpirationDate());
        token.setUser(user);
        return token;
    }

Second Service:

    @Service(value = "resetPasswordService")
    public class ResetPasswordTokenServiceImpl implements TokenService {

    @Override
    public ResetPasswordToken generateToken(User user) {
        ResetPasswordToken token = new ResetPasswordToken();
        token.setToken(generateHash());
        token.setExpirationDate(getExpirationDate());
        token.setUser(user);
        return token;
    }

    public String exampleMethod() {
        return "example"; 
    }

Controller (Trying to access the exampleMethod() ):

@RestController
@RequestMapping("/api/auth")
public class SecurityController {

    private static final Logger logger = LoggerFactory.getLogger(JwtAuthenticationEntryPoint.class);
    private AuthenticationManager authenticationManager;
    private JwtTokenProvider tokenProvider;
    private UserService userService;
    private TokenService resetPasswordService;

    @Autowired
    public SecurityController(
            AuthenticationManager authenticationManager,
            JwtTokenProvider tokenProvider,
            UserService userService,
            TokenService resetPasswordService) {
        this.authenticationManager = authenticationManager;
        this.tokenProvider = tokenProvider;
        this.userService = userService;
        this.resetPasswordService = resetPasswordService;
    }

 @GetMapping("/reset-password/{token}")
    public ResponseEntity<?> resetPasswordRequest(@PathVariable(value = "token") String token) {
      String example = resetPasswordService.exampleMethod();
        return new ResponseEntity<>(HttpStatus.OK);
    }

Why I'm not able to invoke the exampleMethod() method ?

Do I have to declare it in my interface ?

Answer 1

The interface TokenService doesn't declare the method exampleMethod() . So you cannot call that method. You would have to use a cast ((ResetPasswordTokenServiceImpl)resetPasswordService).exampleMethod(); , if resetPasswordService is an instance of ResetPasswordTokenServiceImpl .

If you add that method to the interface, all implementations of TokenService will have to implement that method. For example, EmailTokenServiceImpl doesn't declare that method.

Answer 2

Yes. All your controller knows is that resetPasswordService is an implementation of TokenService .

You could cast resetPasswordService as ResetPasswordTokenServiceImpl but it would be better to instead declare ResetPasswordTokenServiceImpl resetPasswordService explicitly in your constructor.

Don't over-abstract your code. Just explicitly wire in all the necessary implementations of TokenService as their implementing classes. I don't see that there's anything to be gained by treating each different TokenService as instances of the interface.