使用MyBatis对数据库进行增删改查

MyBatis是一种持久层框架，它可以帮助我们轻松地实现数据库操作。下面是使用MyBatis进行增删改查的基本步骤：

1. 配置MyBatis的XML文件（mybatis-config.xml）和映射文件（mapper.xml）。

2. 创建数据库连接，并将连接信息配置到mybatis-config.xml文件中。

3. 在mapper.xml文件中定义SQL语句，包括select、insert、update和delete等操作。

4. 在Java代码中使用SqlSessionFactoryBuilder构建SqlSessionFactory实例，并通过SqlSession获取Mapper实例。

5. 在Java代码中调用Mapper实例的方法执行SQL语句，完成增删改查操作。

下面是一个简单的示例代码：

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/demo/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

2. 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.demo.mapper.UserMapper">
    <resultMap id="userMap" type="com.example.demo.entity.User">
        <id column="id" property="id"/>
        <result column="name" property="name"/>
        <result column="age" property="age"/>
    </resultMap>

    <select id="getUserById" parameterType="int" resultMap="userMap">
        select id, name, age from user where id = #{id}
    </select>

    <select id="getAllUsers" resultMap="userMap">
        select id, name, age from user
    </select>

    <insert id="insertUser" parameterType="com.example.demo.entity.User">
        insert into user (name, age) values (#{name}, #{age})
    </insert>

    <update id="updateUser" parameterType="com.example.demo.entity.User">
        update user set name=#{name}, age=#{age} where id=#{id}
    </update>

    <delete id="deleteUser" parameterType="int">
        delete from user where id=#{id}
    </delete>

</mapper>

3. Java代码

public class UserMapperTest {
    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Test
    public void testGetUserById() {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            User user = userMapper.getUserById(1);
            System.out.println(user);
        } finally {
            sqlSession.close();
        }
    }

    @Test
    public void testGetAllUsers() {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            List<User> userList = userMapper.getAllUsers();
            System.out.println(userList);
        } finally {
            sqlSession.close();
        }
    }

    @Test
    public void testInsertUser() {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            User user = new User("张三", 20);
            userMapper.insertUser(user);
            sqlSession.commit();
            System.out.println(user.getId());
        } finally {
            sqlSession.close();
        }
    }

    @Test
    public void testUpdateUser() {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            User user = new User(1, "李四", 25);
            userMapper.updateUser(user);
            sqlSession.commit();
        } finally {
            sqlSession.close();
        }
    }

    @Test
    public void testDeleteUser() {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            userMapper.deleteUser(1);
            sqlSession.commit();
        } finally {
            sqlSession.close();
        }
    }
}

以上代码演示了通过MyBatis对数据库进行增删改查的基本操作。