MyBatis使用动态代理的方式实现DAO（Mapper）

Mapper接口开发方法只需要程序员编写Mapper接口（相当于Dao接口），由Mybatis框架根据接口定义创建接口的动态代理对象，代理对象的方法体同Dao接口实现类方法。
Mapper接口开发需要遵循以下规范：
1、 Mapper.xml文件中的namespace与mapper接口的类路径相同;
2、 Mapper接口方法名和Mapper.xml中定义的每个statement的id相同 ;
3、 Mapper接口方法的输入参数类型和mapper.xml中定义的每个sql 的parameterType的类型相同;
4、 Mapper接口方法的输出参数类型和mapper.xml中定义的每个sql的resultType的类型相同.

UserMapper接口如下：

package com.sea.crm.mapper;
import java.util.List;
import com.sea.crm.pojo.User;
public interface UserMapper {
	public int save(User user);
	public User queryById(int id);
	public List<User> queryByName(String name);
	public List<User> queryAll();
	public int update(User user);
	public int delete(int id);
}

UserMapper.xml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：命名空间，用于隔离sql>
<mapper namespace="com.sea.crm.mapper.UserMapper">
	<!-- 添加用户 -->
	<insert id="save" parameterType="com.sea.crm.pojo.User">
		insert into user(userName,birthday,sex,address)
		values(#{username},#{birthday},#{sex},#{address})
	</insert>
	
	<!-- 根据ID查询用户 -->
	<select id="queryById" parameterType="int" resultType="com.sea.crm.pojo.User">
		select * from user where id = #{id}
	</select>
	
	<!-- 根据名称模糊查询 -->
	<select id="queryByName" parameterType="string" resultType="com.sea.crm.pojo.User">
		select * from user where username like '%${value}%'
	</select>
	<!-- 查询全部 -->
	<select id="queryAll" resultType="com.sea.crm.pojo.User">
		select * from user
	</select>
	<!--  修改用户信息 -->
	<update id="update" parameterType="com.sea.crm.pojo.User">
		update user set username=#{username},birthday=#{birthday},sex=#{sex},address=#{address} where id=#{id}
	</update>
	
	<!-- 根据ID删除用户 -->
	<delete id="delete" parameterType="int">
		delete from user where id = #{id}
	</delete>
</mapper>

SqlMapConfig.xml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>
	<!-- 和spring整合后 environments配置将废除 -->
	<environments default="development">
		<environment id="development">
			<!-- 使用jdbc事务管理 -->
			<transactionManager type="JDBC" />
			<!-- 数据库连接池 -->
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver" />
				<property name="url"
					value="jdbc:mysql://localhost:3306/seamybatis?characterEncoding=utf-8" />
				<property name="username" value="******" />
				<property name="password" value="******" />
			</dataSource>
		</environment>
	</environments>
	
	<!-- 注册映射文件 -->
	<!-- 将映射文件配置到mybatis的配置文件中 -->
	<mappers>
		<mapper resource="sqlmap/UserMapper.xml"/>
	</mappers>
</configuration>

单元测试这里就写一个添加用户了：

package com.sea.crm.test;
import java.io.InputStream;
import java.util.Date;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;

import com.sea.crm.mapper.UserMapper;
import com.sea.crm.pojo.User;
/**
 * @author Sea You
 *
 * 2018年10月30日上午1:07:06
 */
public class MyBatisTest {
	SqlSessionFactory factory = null;
	private UserMapper userMapper=null;

	@Before
	public void testInit() {
		// 1. 创建SqlSessionFactoryBuilder对象
		SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
		// 2. 加载SqlMapConfig.xml配置文件 
		InputStream in = MyBatisTest.class.getResourceAsStream("/SqlMapConfig.xml");
		// 3. 创建SqlSessionFactory对象
		factory = builder.build(in);
		}
@Test
	public void testSave() {
		User user = new User();
		user.setUsername("尤海");
		user.setBirthday(new Date());
		user.setSex(1);
		user.setAddress("江苏无锡");
		SqlSession session = factory.openSession();
		//通过动态代理实现接口对象
		userMapper = session.getMapper(UserMapper.class);
		userMapper.save(user);
		session.commit();
		session.close();
	}
}

添加测试成功：