Spring Boot登录时UserRepository空指针异常问题求助

使用正确的用户名和密码登录系统时，控制台抛出空指针异常，提示无法调用customlogin.repositories.UserRepository.findByUsername(String)方法，原因是this.userRepository为null。

错误栈信息 #

Caused by: java.lang.NullPointerException: Cannot invoke "customlogin.repositories.UserRepository.findByUsername(String)" because "this.userRepository" is null
at customlogin.service.CustomUserDetailsServices.loadUserByUsername(CustomUserDetailsServices.java:26) ~[classes/:na]
at org.springframework.security.authentication.dao.DaoAuthenticationProvider.retrieveUser(DaoAuthenticationProvider.java:103) ~[spring-security-core-6.2.1.jar:6.2.1]
... 65 common frames omitted

相关代码 #

UserServiceImpl #

package customlogin.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.security.crypto.password.PasswordEncoder;
import org.springframework.stereotype.Service;

import customlogin.dto.UserDto;
import customlogin.model.User;
import customlogin.repositories.UserRepository;


@Service
public class UserServiceImpl  implements UserService{
    
    
    @Autowired
    PasswordEncoder passwordEncoder;
    
    private UserRepository userRepository;
    
    

    public UserServiceImpl(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    @Override
    public User findByUsername(String username) {
        
        return userRepository.findByUsername(username);
    }

    @Override
    public User save(UserDto userDto) {
        User user = new User(userDto.getFullname(), userDto.getDateofbirth(), userDto.getGender(), userDto.getAddress(), userDto.getCity(), userDto.getState(), userDto.getUsername(),passwordEncoder.encode(userDto.getPassword()));
        return userRepository.save(user);
    }

}

UserService #

package customlogin.service;

import customlogin.dto.UserDto;
import customlogin.model.User;

public interface UserService {
    
    User findByUsername(String username);
    User save(UserDto userDto);

}

UserRepository #

package customlogin.repositories;

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

import customlogin.model.User;


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

}

问题分析与解决 #

核心原因 #

错误栈指向CustomUserDetailsServices类的loadUserByUsername方法，说明该类中的userRepository（或依赖的UserService）未被Spring正确注入，导致调用时为null。

解决步骤 #

1. 检查CustomUserDetailsServices的Spring管理与依赖注入

   • 确保类上添加@Service或@Component注解，让Spring容器接管实例创建
   • 使用构造注入方式引入依赖（Spring官方推荐），示例如下：

     @Service
     public class CustomUserDetailsServices implements UserDetailsService {
         private final UserRepository userRepository;
     
         // 构造注入
         public CustomUserDetailsServices(UserRepository userRepository) {
             this.userRepository = userRepository;
         }
     
         @Override
         public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
             User user = userRepository.findByUsername(username);
             // 实现用户信息转换为UserDetails的逻辑
             // ...
         }
     }
     

   • 若依赖的是UserService，则注入UserService即可：

     @Service
     public class CustomUserDetailsServices implements UserDetailsService {
         private final UserService userService;
     
         public CustomUserDetailsServices(UserService userService) {
             this.userService = userService;
         }
     
         @Override
         public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
             User user = userService.findByUsername(username);
             // 后续逻辑
             // ...
         }
     }
     

2. 确保Spring扫描范围正确

   • 检查项目启动类（标注@SpringBootApplication的类）所在包是否包含customlogin及其子包，若不在同一层级，需添加@ComponentScan指定扫描路径：

     @SpringBootApplication
     @ComponentScan(basePackages = "customlogin")
     public class YourApplication {
         public static void main(String[] args) {
             SpringApplication.run(YourApplication.class, args);
         }
     }
     

3. 验证Repository的扫描

   • 确认UserRepository上的@Repository注解存在，且Spring Data JPA的自动扫描功能正常（@SpringBootApplication默认包含@EnableJpaRepositories）

内容的提问来源于stack exchange，提问作者Amit Yadav