做性能优化的最重要的功能就是降低数据库的交互。非常多程序猿一般在开发的时候仅仅考虑简单的实现功能，无论业务简单复杂，仅仅要实现即可。

mybatis有个重要的功能就是考虑在联合查询时技巧：

<?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.cn.dao.TeacherMapper"> 

	 <resultMap type="com.cn.vo.Teacher" id="teacher">
		<id property="id" column="id" javaType="int" jdbcType="INTEGER" />
		<result property="name" column="name" javaType="string"
			jdbcType="VARCHAR" />

		<collection property="students" column="t_s_id" ofType="com.cn.vo.Student">
			<id property="sid" column="sid" javaType="int" jdbcType="INTEGER" />
			<result property="sname" column="sname" javaType="string"
				jdbcType="VARCHAR" />
		</collection>
	</resultMap>

	<select id="one2many" parameterType="int" resultMap="teacher">
		select
		t.id,t.name,s.t_s_id,s.sid,s.sname
		from teacher t join student s on t.id
		= s.t_s_id 
		where t.id = #{id}  
    </select>
 </mapper>  

collection 

mybatis性能优化之降低数据库连接projectdemo下载：

http://download.csdn.net/detail/luozhonghua2014/8953781