Springboot项目中的UserMapper为空

Question

I'm learning spring boot and am working on a toy project - a registration page.

I have a UserMapper interface that interacts with MySQL and it looks something like this:

public interface UserMapper {

    @Insert("INSERT INTO user (email, password, salt, confirmation_code, valid_time, isValid" +
            "VALUES(#{email}, #{password}, #{salt}, #{confirmationCode}, #{validTime}, #{isValid})")
    int insertUser(User user);

In the main class, I added the @MapperScan() annotation so it's supposed to find where the mapper class is.

package com.example;

import...

@MapperScan("com.example.mapper")
@SpringBootApplication(scanBasePackages = "com.example")
public class SpringbootUserLoginApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringbootUserLoginApplication.class, args);
    }
}

Then, I call UserMapper in my UserService class:

@Service
public class UserService {

    private UserMapper userMapper;

    public Map<String, Object> createAccount(User user){
        // this is where the NullPointerException happens
        int result = userMapper.insertUser(user);
        Map<String, Object> resultMap = new HashMap<>();

        if (result > 0) {
            resultMap.put("code", 200);
            resultMap.put("message", "Registration successful, activate account in your email.");
        } else {
            resultMap.put("code", 400);
            resultMap.put("message", "Registration failed");
        }
        return resultMap;
    }
}

The error I got is java.lang.NullPointerException: Cannot invoke "com.example.mapper.UserMapper.insertUser(com.example.pojo.User)" because "this.userMapper" is null .

I also tried adding @Mapper() on the UserMapper interface and still got the same error. Does anyone know why I'm getting this error, and how to fix it? Any help would be greatly appreciated! Thanks!

Answer 1

Autowire Usermapper into UserService class like this:

@Autowired
private UserMapper userMapper;

Answer 2

Or you can use an injection like this :

private final UserMapper userMapper;

public UserService(UserMapper userMapper) {
    this.userMapper = userMapper;
}