（6）MyBatis小总结：一个简单的例子--接口编程改进

本文介绍了如何在MyBatis中使用接口编程方法，通过定义Java接口和XML映射文件来实现数据库操作。具体包括配置环境、定义接口、编写XML映射及测试案例。

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=144@qq.com, gender=0]

效果与此前一样。