java - Spring4中从Service访问Repository时出现NullPointerException

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 6 年前。

我正在尝试使用服务和存储库将通过休息 Controller 发送的用户数据保存到数据库。

Controller

@RestController
@RequestMapping(path="/users")
public class UserController {

    private UserService userService;

    @Autowired
    public UserController(UserService userService) {
        this.userService = userService;
    }

    @RequestMapping(method= RequestMethod.POST, path="/create" )
    @ResponseStatus(HttpStatus.CREATED)
    @ResponseBody
    public void createUser(@RequestBody @Validated UserDto userDto ){

        userService.createUser(userDto.getUsername(), userDto.getEmail(), userDto.getPassword());

    }
}

服务

@Service
public class UserService {

    private UserRepository userRepository;
    private BCryptPasswordEncoder encoder;

    @Autowired
    public UserService(UserRepository userRepository){
        this.userRepository = userRepository;
    }

    public void createUser(String username, String email,String password){

        userRepository.save(new User(username, email, encoder.encode(password))); //line 25
    }

    public Optional<User> getByUsername(String username){
        return userRepository.findByusername(username);
    }
}

存储库

@Repository
public interface UserRepository extends JpaRepository<User, Integer> {
    Optional<User> findByusername(String username);
}

我正在向此 http://localhost:8080/users/create 发送 POST 请求带有以下数据的网址

{
  "username": "testusername",
  "password": "password123",
  "passwordRepeat": "password123",
  "email": "asd@gm.com",
  "emailRepeat": "asd@gm.com"
}

这是我这样做时遇到的异常，

java.lang.NullPointerException: null
    at com.mportal.ec.services.UserService.createUser(UserService.java:25)
    at com.mportal.ec.web.UserController.createUser(UserController.java:33)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

我无法弄清楚这里的原因。请帮忙。

Answer 1

发生这种情况并不是因为您正在访问存储库，而是因为您正在使用 encoder.encode()，即使 BCryptPasswordEncoder 未 Autowiring 。

您有以下字段:

private UserRepository userRepository;
private BCryptPasswordEncoder encoder;

但是您只 Autowiring 了一个:

@Autowired
public UserService(UserRepository userRepository){
    this.userRepository = userRepository;
}

因此，您可以通过将构造函数更改为来修复它:

@Autowired
public UserService(UserRepository userRepository, BCryptPasswordEncoder encoder) {
    this.userRepository = userRepository;
    this.encoder = encoder; // This line is missing
}

不过，您需要有一个可用的 BCryptPasswordEncoder bean。