@Autowired field is null after trying suggestions

Question

I've been trying to encrypt passwords following the tutorial found here https://www.baeldung.com/spring-security-registration-password-encoding-bcrypt. I created my bean, but had the quite common problem that my autowired fields never got injected. I have tried to sort this problem now for quite a while, following various advice on here such as the following resource Why is my Spring @Autowired field null? but none of the help seems to be working, and I'm really not too sure where I am going wrong. I even tried putting the beans in the xml, although I couldn't get this to work either.

Here is my code so far:

User class, where the autowired field is null

@Service
@Configurable
public class User {

    @Id
    private UUID id;
    private long alias;
    private String username;
    private String password;

    @Autowired
    private PasswordEncoder passwordEncoder;

Config class where the bean is getting set up:

@Configuration
public class Config {
    @Bean
    public PasswordEncoder encoder() {
        return new BCryptPasswordEncoder();
    }
}

I'm quite new to spring so I'm sorry if it's a really glaring fix, I just don't know how else to try make it work. Thank you for any help.

Updated code with qualifiers:

config class:

@Configuration
public class Config {
    @Bean("bCryptPasswordEncoder")
    public PasswordEncoder encoder() {
        return new BCryptPasswordEncoder();
    }

user class:

    @Autowired
    @Qualifier("bCryptPasswordEncoder")
    private PasswordEncoder passwordEncoder;

How the user is being instantiated:

@PostMapping("/users")
    public String newUser(@RequestBody User newUser) {
        if (repository.existsByUsername(newUser.getUsername())){
            return new UserAlreadyExistsException(newUser.getUsername()).getMessage(newUser.getUsername(), repository);
        }
        User u = new User(getAlias(repository), newUser.getUsername(), newUser.getPassword());
        repository.save(u);
        return "{\"message\" : \"user\", \"user\" : " + u.toString() + "}";
    }

Answer 1

You are trying to inject interface, spring does not know which implementation to choose from.

To fix this add the following:

@Bean("bCryptPasswordEncoder")
public PasswordEncoder encoder() { 
    return new BCryptPasswordEncoder();
}

and

@Autowired
@Qualifier("bCryptPasswordEncoder")
private PasswordEncoder encoder;

see:

baeldung qualifier

if you are using constructor Injection(highly recommended) you can add the @Qualifier("bCryptPasswordEncoder") in the constuctor before the variable, like so:

public User(@Qualifier("bCryptPasswordEncoder") PasswordEncoder encoder) {
    this.encoder = encoder;
}

P.S.

I would highly recommend using the Spring 5 delegating password encoder for future compatibility

baeldung delegating password encoder examples

P.P.S User is a data member and should not hold password encoder, it is a good design pattern to create separation between data Members and business logic(search spring layer architecture),

If this is a new project I would go a step further and look at the Onion architecture: Onion architecture

P.P.P.s also I would recommend you look at lombok project :)

Answer 2

I created a @Bean in a @Configuration class as you did:

@Bean
public PasswordEncoder encoder() {
    return new BCryptPasswordEncoder();
}

And tried to use @Autowired to a private attribute as you did:

@Autowired
private PasswordEncoder encoder;

I was getting an error saying that encoder is null when trying to encode my passwords as well.

But got it fixed following Michael's suggestion (in the comments):

Don't use field injection. Use constructor injection.

Example:

I have a UserConfig class responsible for populating my database with initial data:

public UserConfig(UserRepository repository, PasswordEncoder passwordEncoder) {
    User user1 = new User(
            "firstUser",
            passwordEncoder.encode("123123"),
            "user1@gmail.com"
            /* . . .*/
    );

    User user2 = new User(
            "anotherUser",
            passwordEncoder.encode("111222"),
            "user2@gmail.com"
            /* . . .*/ 
    );

    repository.saveAll(
            List.of(user1, user2)
    );
}

And now it works as expected.