Hey I am pretty new to using the Spring Framework and was just trying to get an application to work for practice but I am getting the following error in my stack trace: Cannot invoke "com.gabriel.schoolapp.repository.UsersRepo.findAll()" because "this.usersRepo" is null

This is my model layer for the Users:

package com.gabriel.schoolapp.models;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;
import lombok.ToString;

@NoArgsConstructor
@AllArgsConstructor
@Getter
@Setter
@ToString
@Entity
@Table(name = "users")

public class Users {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer usersID;
    
    @Column(nullable = false)
    private String firstName;

    public void FirstName(String firstName){
        this.firstName = firstName;
    }

    @Column(nullable = false)
    private String lastName;

    public void ClassDesc(String lastName){
        this.lastName = lastName;
    }

    @Column(nullable = false)
    private String username;

    public void Username(String username){
        this.username = username;
    }
}

This is my repository layer:

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import com.gabriel.schoolapp.models.Users;

@Repository
public interface UsersRepo extends JpaRepository<Users, Integer>{

    Users findByUsername(String firstName);
    
}

And this is my service layer:

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.gabriel.schoolapp.models.Users;
import com.gabriel.schoolapp.repository.UsersRepo;

@Service
public class UsersService {
    @Autowired
    private UsersRepo usersRepo;

    
    @Autowired
    public UsersService(UsersRepo usersRepo){
        
        this.usersRepo = usersRepo;
    }

    public UsersService(){

    }

     public Users createUser(Users user){
        Users checkIfUserInDb = usersRepo.findByUsername(user.getFirstName());

        if(checkIfUserInDb != null){
            System.out.println("Username already in DB");
            return null;
        }
        System.out.println("User is valid");
        return usersRepo.save(user);
    } 

    public List<Users> getAllUsersById(){
        return this.usersRepo.findAll();
    }
}

Whenever I try to call a method from the service layer like so:

@SpringBootApplication
public class SchoolAppApplication {

    public static void main(String[] args) {
        SpringApplication.run(SchoolAppApplication.class, args);
        
        UsersService serv = new UsersService();
        serv.getAllUsersById();
        
    }

}

It returns with the aforementioned error (this.usersRepo is null)

Any help would be greatly appreciated thank you!!

CodePudding user response：

The UserService you created is not managed by Spring, hence the repo is not autowired. You need a few things:

1. implement CommandLineRunner in SchoolAppApplication
2. Autowire your service in SchoolAppApplication
3. Override method run in SchoolAppApplication and run your service there:

    @Override
    public void run(String... args) {
        serv.getAllUsersById();
    }