（6）MyBatis小总结：一个简单的例子--接口编程改进

日期：2017/12/6

一、回顾 java 的 interface 语法：特殊的抽象类 + 方法必须无实体。（参考   Java（4）：基础：面向对象学习的重要点  ）

二、回顾sql在User.xml的封装（namespace + id）：(（5）MyBatis小总结：一个简单的例子)

<?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="User">      <select id="selectUser" resultType="mybatis.User">          select * from employee where id=#{id}  
三、Mybatis的接口编程，恰好是使用 interface_name + method_name 组成唯一的 sql 设定。
3.1 UserImp.java
package mybatis;//运用OOP编程思想，给xml做过改进 --- 接口编程public interface UserImp {//定义方法，interface 只能定义方法，无法实现方法体。public User getUserById(Integer id);}

3.2 改进后的 User.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="mybatis.UserImp">    <select id="getUserById" resultType="mybatis.User">select * from employee where id=#{id}    </select></mapper>

3.3 configuration.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="" />            </dataSource>        </environment>    </environments>    <mappers>        <mapper resource="mybatis/User.xml" />    </mappers></configuration>

3.4 testcase2.java

package mybatis;import java.io.IOException;import java.io.Reader;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 testcase2 {public static void main(String [] args) throws IOException{        String resource = "mybatis/configuration.xml";          Reader reader = Resources.getResourceAsReader(resource);          SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);          SqlSession session = sessionFactory.openSession();          try{        //获得 接口对象        UserImp usermapper = session.getMapper(UserImp.class);        User user = usermapper.getUserById(1);        System.out.println(user);        }finally{        session.close();        }}}

测试结果：

log4j:WARN No appenders could be found for logger (org.apache.ibatis.logging.LogFactory).log4j:WARN Please initialize the log4j system properly.
Employee [id=1, lastName=mmb, email=[e-mail], gender=0]

效果与此前一样。