Spring MVC - 静态上下文中的 Autowired Repository NullPointerException

Question

In my model I have a repository called UserRepository . Additionally I have a UserFacade that basically adds the user to the repository and is accessed by the Controller. The repo is @Autowired in the Facade. When I want to add a new user I get a nullPointerException for the repository.

My spring-servlet.xml contains the required

<jpa:repositories base-package="project.user.repositories" />

while repositories is the folder containing the UserRepository.java . It extends the CrudRepository:

@Repository
public interface UserRepository extends CrudRepository<User, Long> {
    User findByUsername(String username);
}

Facade.java is the object containing repository:

public class UserFacade {
    @Autowired
    private static UserRepository userRepo;

    private static Logger logger = LoggerFactory.getLogger(UserFacade.class);

    public UserFacade(){} //Thought it might work if I add a constructor and call it?

    public static User findByUsername(String username) {
        logger.debug(username+userRepo);  // prints SomeStringnull
        return userRepo.findByUsername(username); //NullPointerException
    }
}

And from my controller I have a method like:

@RequestMapping(value = CONTEXT)
public String test(){
    User user = UserFacade.findByUsername("get"); 
    //obviously user will be null if there is no such user
    return "success";
}

Imports will should not be a problem as I am using Android Studio. What did I miss?

Note: There are many great answers to related questions (like this one ), but each has it's own, different context and didn't help me.

Answer 1

Spring doesn't autowire static fields. That is why userRepo field is null . One way is to make the UserFacade a bean itself, and then you can make userRepo a non-static field. I would prefer this way. UserFacade shouldn't really be a utility class, since it is interacting with the repository bean. It would make much more sense to make it a bean.

Another option is to provide a setter, and use @Autowired on that:

@Autowired
public void setUserRepo(UserRepository userRepo) {
    UserFacade.userRepo = userRepo;
}

Or using it even on a parameterized constructor would work.