转自：https://blog.csdn.net/two_people/article/details/51759881
在学习mybatis的时候我们通常会在映射文件这样写：
<?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.qbd.mapper.StudentMappers">
<select id="findbyid" parameterType="Integer" resultMap="StudentResult">
select *from student where id=#{id}
</select> <select id="findbygradeid" parameterType="Integer" resultMap="StudentResult">
select *from student where gid=#{gid}
</select> <resultMap type="Student" id="StudentResult">
<id property="id" column="id"/>
<result property="name" column="name"/>
<result property="age" column="age"/>
<association property="address" column="addid" select="com.qbd.mapper.AddressMappers.findbyid">
</association>
<association property="grade" column="gid" select="com.qbd.mapper.GradeMappers.findbyid">
</association>
</resultMap>
</mapper>
来读取配置文件
另一种方法就是：
直接在mapper.xml中的这一部分写成dao<mapper namespace="com.qbd.mapper.StudentMappers">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">
<mapper namespace="com.qbd.ssm.dao.UserDao">
<!-- 定义缓存 一般是一级缓存，如果用同一个sqlsession 那么相同查询直接会从缓存中查找
<cache size="1024" flushInterval="60000" eviction="LRU" readOnly="false"></cache>
-->
<!-- 查找所有 -->
<select id="find" parameterType="Map" resultMap="StudentResult">
select * from user
<where>
<if test="uname!=null and uname!='' ">
and uname like #{uname}
</if>
</where>
<if test="start!=null and size!=null">
limit #{start},#{size}
</if>
</select> <select id="getTotal" parameterType="Map" resultType="Long">
select count(*) from user
<where>
<if test="uname!=null and uname!='' ">
and uname like #{uname}
</if>
</where>
</select>
<!-- 按照用户名和密码查找 -->
<select id="getUser" resultMap="StudentResult" parameterType="Map">
select *from user where uname=#{uname} and upassword=#{upassword}
</select>
<!-- 删除 -->
<delete id="delete" parameterType="Map">
delete from user where uid=#{uid}
</delete>
<!-- 修改 -->
<update id="update" parameterType="User">
update user
<set>
<if test="uname!=null">
uname=#{uname},
</if>
<if test="upassword!=null">
upassword=#{upassword},
</if>
<if test="upower!=null">
upower=#{upower},
</if>
</set>
where uid=#{uid}
</update>
<!-- 增加 -->
<insert id="add" parameterType="User">
insert into user values(null,#{uname},#{upassword},#{upower})
</insert>
<resultMap type="User" id="StudentResult">
<id property="uid" column="uid"/>
<result property="uname" column="uname"/>
<result property="upassword" column="upassword"/>
</resultMap>
</mapper>
那么就不用写dao的实现在service中就能掉用 mybatis默认会把mapper.xml映射为dao的实现