不使用mybatis-plus呢

不使用MyBatis-Plus的话，可以使用原生的MyBatis框架来进行数据库操作。MyBatis是一个开源的持久层框架，它支持自定义SQL、存储过程以及高级映射。以下是一个使用MyBatis进行数据库操作的例子：

1. 配置文件mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
  <environments default="development">
    <environment id="development">
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/test"/>
        <property name="username" value="root"/>
        <property name="password" value="root"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>
    <mapper resource="com/example/mapper/UserMapper.xml"/>
  </mappers>
</configuration>

2. 实体类User.java

public class User {
    private Long id;
    private String name;
    private Integer age;
    // 省略getter和setter方法
}

3. Mapper接口UserMapper.java

public interface UserMapper {
    User selectUserById(Long id);
    List<User> selectAllUsers();
    void insertUser(User user);
    void updateUser(User user);
    void deleteUserById(Long id);
}

4. Mapper映射文件UserMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.mapper.UserMapper">
  <resultMap id="userMap" type="User">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <result property="age" column="age"/>
  </resultMap>
  <select id="selectUserById" resultMap="userMap">
    select * from user where id = #{id}
  </select>
  <select id="selectAllUsers" resultMap="userMap">
    select * from user
  </select>
  <insert id="insertUser">
    insert into user(name, age) values(#{name}, #{age})
  </insert>
  <update id="updateUser">
    update user set name=#{name}, age=#{age} where id=#{id}
  </update>
  <delete id="deleteUserById">
    delete from user where id=#{id}
  </delete>
</mapper>

5. 使用MyBatis进行数据库操作

public class MyBatisDemo {
    public static void main(String[] args) {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            User user = userMapper.selectUserById(1L);
            System.out.println(user.getName());
            List<User> userList = userMapper.selectAllUsers();
            for (User u : userList) {
                System.out.println(u.getName());
            }
            User newUser = new User();
            newUser.setName("Tom");
            newUser.setAge(20);
            userMapper.insertUser(newUser);
            newUser.setName("Jerry");
            newUser.setAge(21);
            userMapper.updateUser(newUser);
            userMapper.deleteUserById(2L);
            sqlSession.commit();
        } finally {
            sqlSession.close();
        }
    }
}