如何使用MyBatis

介绍

MyBatis 是一款优秀的持久层框架，它支持定制化 SQL、存储过程以及高级映射。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以使用简单的 XML 或注解来配置和映射原生信息，将接口和 Java 的 POJOs(Plain Old Java Objects,普通的 Java对象)映射成数据库中的记录。

下载

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.4.5</version>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.6</version>
</dependency>

配置

• conf.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>
    <properties resource="db.properties"/><!-- 使用属性文件 -->
    <typeAliases><!-- 为User取别名 -->
        <typeAlias type="com.fleming.domain.User" alias="_User"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <!-- JDBC配置 -->
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="${driver}" />
                <property name="url" value="${url}" />
                <property name="username" value="${name}" />
                <property name="password" value="${pass}" />
            </dataSource>
        </environment>
    </environments>
</configuration>

• 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.fleming.mapping.userMapper">
    <select id="getUser" parameterType="int" resultType="_User">
        select * from users where id=#{id}
    </select>
    <insert id="insertUser" parameterType="_User">
        insert into users(name,age) values(#{name},#{age})
    </insert>
    <delete id="delUser" parameterType="int">
        delete from users where id=#{id}
    </delete>
    <update id="updateUser" parameterType="_User">
        update users set name=#{name},age=#{age} where id=#{id}
    </update>
    <select id="getAllUsers" parameterType="_User">
        select * from users
    </select>
</mapper>

• 利用注解编写接口UserMapperI.java

public interface UserMapperI {
    //使用@Insert注解指明add方法要执行的SQL
    @Insert("insert into users(name, age) values(#{name}, #{age})")
    public int add(User user);
    
    //使用@Delete注解指明deleteById方法要执行的SQL
    @Delete("delete from users where id=#{id}")
    public int deleteById(int id);
    
    //使用@Update注解指明update方法要执行的SQL
    @Update("update users set name=#{name},age=#{age} where id=#{id}")
    public int update(User user);
    
    //使用@Select注解指明getById方法要执行的SQL
    @Select("select * from users where id=#{id}")
    public User getById(int id);
    
    //使用@Select注解指明getAll方法要执行的SQL
    @Select("select * from users")
    public List<User> getAll();
}

使用注解可以方便调用，然后将mapper文件配置到conf.xml中

<mappers>
    <mapper resource="com/fleming/mapping/userMapper.xml" />
    <mapper class="com.fleming.mapping.UserMapperI" />
</mappers>

测试

-- ----------------------------
--  Table structure for `users`
-- ----------------------------
DROP TABLE IF EXISTS `users`;
CREATE TABLE `users` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(20) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records 
-- ----------------------------
INSERT INTO `users` VALUES ('1','独孤求败','27'), ('2','独孤求败','27'), ('3','独孤求败','20');

public class MybatisTest {
    @Test
    public void testGetAll(){
        String resource = "conf.xml";
        InputStream is = MybatisTest.class.getClassLoader().getResourceAsStream(resource);
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);    
        SqlSession session = sessionFactory.openSession();
        /**
         * 映射sql的标识字符串，
         * me.gacl.mapping.userMapper是userMapper.xml文件中mapper标签的namespace属性的值，
         * getAllUsers是select标签的id属性值，通过select标签的id属性值就可以找到要执行的SQL
         */
        UserMapperI mapper = sqlSession.getMapper(UserMapperI.class);
        //执行查询操作，将查询结果自动封装成List<User>返回
        List<User> lstUsers = mapper.getAll();
        //使用SqlSession执行完SQL之后需要关闭SqlSession
        sqlSession.close();
        for(User user: lstUsers) {
            System.out.println(user);
        }
    }   
}

基本入门操作，留作记录。