1、什么是MyBatis?
MyBatis源自Apache的iBatis开源项目, 从iBatis3.x开始正式更名为MyBatis。它是一个优秀的持久层框架。
官网地址:http://www.mybatis.org/mybatis-3/
2、为什么使用MyBatis?
为了和数据库进行交互,通常的做法是将SQL语句写在Java代码中,SQL语句和Java代码耦合在一起不利于后期维护修改,
而MyBatis能够帮助我们将SQL语句和Java代码分离,方便了后期因需求变动而对SQL语句进行修改。(联系properties文件的作用)
3、如何使用MyBatis
①、准备
a、下载MyBatis相应jar包:https://github.com/mybatis/mybatis-3/releases
b、创建Java工程,导入MyBatis jar包(mybatis-3.4.4.jar)和数据库驱动包
c、创建user_info表并添加数据
create table user_info( id char(36) primary key, user_name varchar(15) unique, password varchar(15) not null ) insert into user_info (id, user_name, password) values ('3ddcf637-15a8-49d9-a378-b3fa2f2f9c65', 'Aimee', '1983_2560x'); insert into user_info (id, user_name, password) values ('7eb9deed-ec87-416e-abb3-1a5a2ce819de', 'Cassie', 'xm@560_lq');
②、使用
a、第一种使用方法:
i、在com.lq.test包中创建名为Test的类,写入如下代码:
package com.lq.test; import java.io.IOException; import java.io.InputStream; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; public class Test { public static void main(String[] args) throws IOException { InputStream inputStream = Resources.getResourceAsStream("config/mybatis-config.xml"); //获取SqlSessionFactory对象 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //获取SqlSession对象,代表与数据库的一次会话,用完需要关闭。注意:由于SqlSession为非线程安全的,所以该变量应定义为局部变量,不要定义成全局变量 SqlSession sqlSession = sqlSessionFactory.openSession(); try { //调用SqlSession对象selectOne方法执行SQL语句:第一个参数用于指定执行哪个命名空间中的哪个SQL语句,第二个参数即UserInfo id值 String name = sqlSession.selectOne("com.lq.userinfo.selectUserNameById", "3ddcf637-15a8-49d9-a378-b3fa2f2f9c65"); //打印输出 System.out.println(name); } finally { //释放资源 sqlSession.close(); } } }
ii、在config包中创建名为mybatis-config.xml的xml文件,写入如下代码:
<?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"> <!-- 配置数据库连接信息 --> <environment id="development"> <transactionManager type="JDBC" /> <dataSource type="POOLED"> <property name="driver" value="oracle.jdbc.driver.OracleDriver" /> <property name="url" value="jdbc:oracle:thin:@127.0.0.1:1521:keeper" /> <property name="username" value="scott" /> <property name="password" value="root" /> </dataSource> </environment> </environments> <!-- 注册Mapper xml文件 --> <mappers> <mapper resource="./config/UserInfoMapper.xml" /> </mappers> </configuration>
iii、在config包中创建名为UserInfoMapper.xml的xml文件,写入如下代码:
<?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"> <!-- namespace:命名空间; --> <mapper namespace="com.lq.userinfo"> <!-- id:唯一标识;resultType:返回值类型; --> <select id="selectUserNameById" resultType="java.lang.String"> <!-- #{id}:从传递过来的参数中取出id值 --> select user_name from user_info where id = #{id} </select> </mapper>
说明:这种配置方式在为SQL语句传数据时由于参数类型为Object,所以隐藏类型安全问题。
b、第二种使用方法:
i、在com.lq.userinfo包创建IUserInfo接口,代码如下:
package com.lq.userinfo; public interface IUserInfo { String selectUserNameById(String id); }
ii、在com.lq.test包创建Test类,代码如下:
package com.lq.test; import java.io.IOException; import java.io.InputStream; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import com.lq.userinfo.IUserInfo; public class Test { public static void main(String[] args) throws IOException { InputStream inputStream = Resources.getResourceAsStream("config/mybatis-config.xml"); //获取SqlSessionFactory对象 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //获取SqlSession对象,代表与数据库的一次会话,用完需要关闭。注意:由于SqlSession为非线程安全的,所以该变量应定义为局部变量,不要定义成全局变量 SqlSession sqlSession = sqlSessionFactory.openSession(); try { //获取IUserInfo接口实现类对象 IUserInfo userInfo = sqlSession.getMapper(IUserInfo.class); //调用selectUserNameById方法获取userName String userName = userInfo.selectUserNameById("3ddcf637-15a8-49d9-a378-b3fa2f2f9c65"); //打印输出 System.out.println(userName); } finally { //释放资源 sqlSession.close(); } } }
iii、在config包创建名为mybatis-config.xml的xlm文件,代码如下:
<?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"> <!-- 配置数据库连接信息 --> <environment id="development"> <transactionManager type="JDBC" /> <dataSource type="POOLED"> <property name="driver" value="oracle.jdbc.driver.OracleDriver" /> <property name="url" value="jdbc:oracle:thin:@127.0.0.1:1521:keeper" /> <property name="username" value="scott" /> <property name="password" value="root" /> </dataSource> </environment> </environments> <!-- 注册Mapper xml文件 --> <mappers> <mapper resource="./config/UserInfoMapper.xml" /> </mappers> </configuration>
ⅳ、在config包创建名为UserInfoMapper.xml的xlm文件,代码如下:
<?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"> <!-- namespace:必须为接口的全类名 --> <mapper namespace="com.lq.userinfo.IUserInfo"> <!-- id:接口中定义的抽象方法名;resultType:返回值类型 --> <select id="selectUserNameById" resultType="java.lang.String"> <!-- #{id}:从传递过来的参数中取出id值 --> select user_name from user_info where id = #{id} </select> </mapper>
说明:这种方法不仅实现了SQL语句的分离,而且弥补了第一种方法的不足,所以推荐使用这种MyBatis使用方式。
c、第三种使用方法:
i、在com.lq.userinfo包创建IUserInfo接口,代码如下:
package com.lq.userinfo; import org.apache.ibatis.annotations.Select; public interface IUserInfo { @Select("select user_name from user_info where id = #{id}") String selectUserNameById(String id); }
ii、在com.lq.test包创建Test类,代码如下:
package com.lq.test; import java.io.IOException; import java.io.InputStream; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import com.lq.userinfo.IUserInfo; public class Test { public static void main(String[] args) throws IOException { InputStream inputStream = Resources.getResourceAsStream("config/mybatis-config.xml"); //获取SqlSessionFactory对象 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //获取SqlSession对象,代表与数据库的一次会话,用完需要关闭。注意:由于SqlSession为非线程安全的,所以该变量应定义为局部变量,不要定义成全局变量 SqlSession openSession = sqlSessionFactory.openSession(); try { //获取IUserInfo接口实现类对象 IUserInfo userInfo = openSession.getMapper(IUserInfo.class); //调用selectUserNameById方法获取userName String userName = userInfo.selectUserNameById("3ddcf637-15a8-49d9-a378-b3fa2f2f9c65"); //打印输出 System.out.println(userName); } finally { //释放资源 openSession.close(); } } }
iii、在config包创建名为mybatis-config.xml的xlm文件,代码如下:
<?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"> <!-- 配置数据库连接信息 --> <environment id="development"> <transactionManager type="JDBC" /> <dataSource type="POOLED"> <property name="driver" value="oracle.jdbc.driver.OracleDriver" /> <property name="url" value="jdbc:oracle:thin:@127.0.0.1:1521:keeper" /> <property name="username" value="scott" /> <property name="password" value="root" /> </dataSource> </environment> </environments> <!-- 注册Mapper xml文件 --> <mappers> <!-- class属性为接口全名 --> <mapper class="com.lq.userinfo.IUserInfo"/> </mappers>
说明:这种方式不仅使得SQL语句与Java代码出现了耦合,而且不便于写复杂的SQL语句,比如依照可以依照多个字段查询时,where关键字后面的条件是动态的,这时就不便于使用注解的方式写该SQL语句。