<dependency>
      <groupId>tk.mybatis</groupId>
      <artifactId>mapper-spring-boot-starter</artifactId>
      <version>2.1.5</version>
    </dependency>

@Setter
@Getter
@Table(name = "user")
public class User {
    /**
     * 用戶ID
     */
    @Id
    private String id;
    /**
     * 用戶姓名
     */
    private String userName;
    /**
     * 用戶密碼
     */
    private String passWord;
    /**
     * 年齡
     */
    private Integer age;
    /**
     * 性別
     */
    private String gender;
}

@Mapper
public interface UserMapper extends Mapper<User>, MySqlMapper {
}

@Service
public class UserService {
    @Resource
    private UserMapper userMapper;
    /**
     *  根據(jù)主鍵字段進行查詢，方法參數(shù)必須包含完整的主鍵屬性，查詢條件使用等號
     */
    public User selectUserById(String userId){
        return userMapper.selectByPrimaryKey(userId);
    }
    /**
     *  查詢?nèi)拷Y(jié)果
     */
    public List<User> selectAll(){
        return userMapper.selectAll();
    }
    /**
     *  根據(jù)實體中的屬性值進行查詢，查詢條件使用等號
     */
    public List<User> selectByUserName(String userName){
        User user = new User();
        user.setUserName(userName);
        return userMapper.select(user);
    }
    /**
     *  根據(jù)實體中的屬性進行查詢，只能有一個返回值，有多個結(jié)果是拋出異常，查詢條件使用等號。
     *  但是如果存在某個屬性為int，則會初始化為0?？赡苡绊懙綄嶋H使用
     */
    public User selectOneByUserName(String userName){
        User user = new User();
        user.setUserName(userName);
        return userMapper.selectOne(user);

    }
    /**
     *  根據(jù)實體中的屬性查詢總數(shù)，查詢條件使用等號
     */
    public Integer selectUserCount(String userName){
        User user = new User();
        user.setUserName(userName);
        return userMapper.selectCount(user);
    }
    /**
     *  保存一個實體，null的屬性也會保存，不會使用數(shù)據(jù)庫默認值
     */
    public void addUser(String userName,String passWord,Integer age,String gender){
        User user = new User();
        user.setId(String.valueOf(UUID.randomUUID()));
        user.setUserName(userName);
        user.setAge(age);
        user.setGender(gender);
        user.setPassWord(passWord);
        userMapper.insert(user);
    }
    /**
     *  保存一個實體，忽略空值，即沒提交的值會使用使用數(shù)據(jù)庫默認值
     */
    public void addUserService(String userName,String passWord){
        User user = new User();
        user.setId(String.valueOf(UUID.randomUUID()));
        user.setUserName(userName);
        user.setPassWord(passWord);
        userMapper.insertSelective(user);
    }
    /**
     *  根據(jù)主鍵字段進行刪除，方法參數(shù)必須包含完整的主鍵屬性
     */
    public void deleteById(String userId){
        userMapper.deleteByPrimaryKey(userId);
    }
    /**
     *  根據(jù)實體屬性作為條件進行刪除，查詢條件使用等號
     */
    public void deleteByName(String userName){
        User user = new User();
        user.setUserName(userName);
        userMapper.delete(user);
    }
    /**
     *  根據(jù)主鍵更新實體全部字段，null值會被更新
     */
    public void updateById(String userId,String userName){
        User user = new User();
        user.setId(userId);
        user.setUserName(userName);
        userMapper.updateByPrimaryKey(user);
    }
    /**
     *  根據(jù)主鍵更新屬性不為null的值
     */
    public void updateByIdSelective(String userId,String userName){
        User user = new User();
        user.setId(userId);
        user.setUserName(userName);
        userMapper.updateByPrimaryKeySelective(user);
    }    
}

@Mapper
public interface UserMapper extends Mapper<User>, SelectByIdsMapper, DeleteByIdsMapper {
}

     /**
     *  批量查詢
     */
    public List<User> selectUserById(List<String> userIds){
        StringJoiner stringJoiner = new StringJoiner(",");
        for (String userId : userIds) {
            stringJoiner.add(userId);
        }
        return userMapper.selectByIds(stringJoiner.toString());
    }
    /**
     *  根據(jù)ID批量刪除
     */
    public void deleteById(List<String> userIds){
        StringJoiner stringJoiner = new StringJoiner(",");
        for (String userId : userIds) {
            stringJoiner.add(userId);
        }
        userMapper.deleteByIds(stringJoiner.toString());
    } 

@Mapper
public interface UserMapper extends Mapper<User>, MySqlMapper, SelectByIdsMapper, DeleteByIdsMapper {
}

    /**
     *  批量添加
     */
    public void batchAdd(){
       List<User> list = new ArrayList();
        for (int i = 1; i < 6; i++) {
            User user = new User();
            user.setId(String.valueOf(i));
            user.setUserName("zs");
        }
        userMapper.insertList(list);
    }

Example example = new Example(User.class);
Example.Criteria criteria = example.createCriteria();

    public List<User> getUserByExample(String userName,String age){
        Example example = new Example(User.class);
        //Example.Criteria criteria = example.and();  
        //criteria.andEqualTo("age",age)  這里直接簡寫了
        example.and().andEqualTo("age",age)
                .andLike("userName",'%' +userName + '%');
        List<User> users = userMapper.selectByExample(example);
        return users;
    }