mybatismapper怎么写

MyBatis是一种支持定制化SQL、存储过程和高级映射的优秀的持久层框架，它的Mapper接口是MyBatis的一个重要组成部分，用于将Java方法与SQL语句进行映射。下面是一个简单的MyBatis Mapper的写法示例：

1. 定义实体类

public class User {
    private Integer id;
    private String username;
    private String password;
    // 省略getter/setter方法
}

2. 编写Mapper映射文件

在resources目录下创建mapper目录，并在mapper目录下创建UserMapper.xml文件，该文件用于定义SQL语句和映射关系。

<?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">

  <!-- 定义查询语句 -->
  <select id="getUserById" parameterType="int" resultType="User">
    select * from user where id = #{id}
  </select>

  <!-- 定义插入语句 -->
  <insert id="addUser" parameterType="User">
    insert into user(username, password) values(#{username}, #{password})
  </insert>

  <!-- 定义更新语句 -->
  <update id="updateUser" parameterType="User">
    update user set username = #{username}, password = #{password} where id = #{id}
  </update>

  <!-- 定义删除语句 -->
  <delete id="deleteUserById" parameterType="int">
    delete from user where id = #{id}
  </delete>

</mapper>

3. 编写Mapper接口

在Java包com.example.mapper下创建UserMapper接口，该接口用于定义方法与SQL的映射关系。

public interface UserMapper {
    User getUserById(int id);
    void addUser(User user);
    void updateUser(User user);
    void deleteUserById(int id);
}

4. 配置MyBatis

在resources目录下创建mybatis-config.xml文件，该文件用于配置MyBatis的全局属性和插件。

<?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="mapper/UserMapper.xml"/>
  </mappers>
</configuration>

5. 使用Mapper

public class Main {
    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();

        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        User user = userMapper.getUserById(1);
        System.out.println(user);

        sqlSession.close();
    }
}

以上是一个简单的MyBatis Mapper的写法示例，具体的实现方式可以根据具体的业务需求进行调整和优化。