Mybatis快速入门

Mybatis开发步骤

1. 添加依赖坐标

<dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.11</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.1</version>
        </dependency>

2. 编写POJO映射文件，如UserMapper.xml 可放在resource资源目录下，注意.和/的区别

<?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="userMapper">
    <select id="findAll" resultType="com.rsk.entity.User">
        select * from user
    </select>
</mapper>

3. 编写mybatis配置文件，mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <!--数据源环境-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/test_db?serverTimezone=GMT%2B8"/>
                <property name="username" value="root"/>
                <property name="password" value=""/>
            </dataSource>
        </environment>
    </environments>
    <!--加载映射文件-->
    <mappers>
        <mapper resource="com/rsk/mapper/UserMapper.xml"></mapper>
    </mappers>
</configuration>

4. 编写测试类

public class Test1 {
    @Test
    public void test1() throws IOException {
        //获得核心配置文件
        InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
        //获得sqlSession工厂
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        //获得session会话对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //执行操作
        List<User> users = sqlSession.selectList("userMapper.findAll");
        System.out.println(users);
        //释放资源
        sqlSession.close();

    }
}

Mybatis传统增删改查方式

mapper.xml

<mapper namespace="userMapper">
    <!--查询操作-->
    <select id="findAll" resultType="com.rsk.entity.User">
        select * from user
    </select>
    <!--插入操作-->
    <insert id="addUser" parameterType="com.rsk.entity.User">
        insert into user values(#{id},#{name},#{pwd})
    </insert>
    <!--更新操作-->
    <update id="update" parameterType="com.rsk.entity.User">
        update user set name=#{name},pwd=#{pwd} where id=#{id}
    </update>
    <!--删除操作-->
    <delete id="delete" parameterType="java.lang.Integer">
        delete from user where id=#{id}
    </delete>
</mapper>

Test.java

//获得核心配置文件
        InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
        //获得sqlSession工厂
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        //获得session会话对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //查询操作
        //List<User> users = sqlSession.selectList("userMapper.findAll");
        //插入操作
        //int insert = sqlSession.insert("userMapper.addUser", user);
        //更新操作
        //sqlSession.update("userMapper.update", user);
        //删除操作
        sqlSession.delete("userMapper.delete", 26);
        sqlSession.commit();
        //释放资源
        sqlSession.close();

Mybatis核心标签

1. properties：加载外部的properties文件

<!--通过标签加载外部properties文件-->
 <properties resource="jdbc.properties"></properties>

2. typeAliases：设置类型别名,该标签必须在environments标签上面

<!--别名设置-->
    <typeAliases>
        <typeAlias type="com.rsk.entity.User" alias="user"></typeAlias>
    </typeAliases>

3. mappers：加载映射配置

<!--加载映射文件-->
    <mappers>
        <mapper resource="com/rsk/mapper/UserMapper.xml"></mapper>
    </mappers>

4. enviroments：数据库环境配置标签

<!--数据源环境-->
    <environments default="development">
        <environment id="development">
            <!--指定事务管理类型，为JDBC(依赖数据源获得连接来管理事务)或者MANAGED(让容器管理事务，默认情况下会关闭连接)-->
            <transactionManager type="JDBC"></transactionManager>
            <!--指定数据源类型，UNPOOLED(数据源每次被请求时候打开或者关闭连接，POOLED(利用连接池将JDBC对象组织起来)，JNDI(用于EJB或者应用服务器容器使用))-->
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}?serverTimezone=GMT%2B8"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value=""/>
            </dataSource>
        </environment>
    </environments>

Mybatis代理实现DAO层

采用Mybatis的代理开发实现DAO层，我们只需要编写Mapper接口（相当于DAO接口），然后由Mybatis框架根据接口定义创建接口的动态代理对象，该动态代理对象的方法体相当于是DAO层的实现类方法。遵循以下规范：

• Mapper.xml中的namespace与mapper接口的全限定名称相同
• Mapper.xml中的每个statement的id和Mapper接口方法名相同
• Mapper.xml中的每个sql的parameterType与和Mapper接口方法的输入参数类型相同
• Mapper.xml中的每个sql的resultType与和Mapper接口方法的返回参数类型相同

1. 编写DAO接口UserMapper.class

public interface UserMapper {
    public List<User> findAll() throws IOException;
    public User findById(int id);
}

2. 编写映射文件UserMapper.xml，namespace需要指定到DAO接口的位置

<?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.rsk.dao.UserMapper">
    <!--查询操作-->
    <select id="findAll" resultType="user">
        select * from user
    </select>
    <select id="findById" parameterType="int" resultType="user">
        select * from user where id=#{id}
    </select>
    <!--插入操作-->
    <insert id="addUser" parameterType="com.rsk.entity.User">
        insert into user values(#{id},#{name},#{pwd})
    </insert>
    <!--更新操作-->
    <update id="update" parameterType="com.rsk.entity.User">
        update user set name=#{name},pwd=#{pwd} where id=#{id}
    </update>
    <!--删除操作-->
    <delete id="delete" parameterType="java.lang.Integer">
        delete from user where id=#{id}
    </delete>
</mapper>

3. Service调用sqlSession的getMapper方法

public class ServiceDemo {
    public static void main(String[] args) throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> all = userMapper.findAll();
        User user = userMapper.findById(1);
        System.out.println(all);
        System.out.println(user.getName());

    }
}