原始使用方式

//下面这句可以用单例模式
public SqlSession sqlSession = (new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("sqlMapConfig.xml"))).openSession();
MyDao mapper = sqlSession.getMapper(MyDao.class);
System.out.println("--------------insert---------------");

MyNew insertNew = new MyNew("insert", "123", "testInsert", new Date());

System.out.println(mapper.insert(insertNew));

System.out.println("insertNew.getId() = " + insertNew.getId());

sqlSession.commit();
System.out.println("--------------getAll---------------");

List<MyNew> res = mapper.getAll();

res.forEach(System.out::println);
System.out.println("--------------getOneById---------------");

System.out.println((mapper.getOneById(19)).toString());
System.out.println("--------------getAllByLikeCase---------------");

(mapper.getAllByLikeCase("i")).forEach(System.out::println);
System.out.println("--------------update---------------");

MyNew updateNew = new MyNew("update", "123", "testUpdate", new Date());

updateNew.setId(19);

System.out.println(mapper.update(updateNew));

sqlSession.commit();
System.out.println("--------------delete---------------");

System.out.println(mapper.delete("insert"));

sqlSession.commit();

<?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>

<properties resource="db.properties"> </properties>

<settings>

<setting name="logImpl" value="STDOUT_LOGGING"/> <!--往console里输出日志-->

<!--  开启懒加载  -->

<setting name="lazyLoadingEnabled" value="true"/>

<setting name="aggressiveLazyLoading" value="false"/>

<!-- 开启二级缓存 -->

<setting name="cacheEnabled" value="true"/>

</settings>
&lt;typeAliases&gt;&lt;!--起别名--&gt;

<!--        <typeAlias alias="Post" type="com.ljj.entity.Post"/>-->

<package name="com.ljj.entity"/>

<package name="com.ljj.dao"/>

</typeAliases>
&lt;environments default=&quot;ljj&quot;&gt;
    &lt;environment id=&quot;ljj&quot;&gt;
        &lt;transactionManager type=&quot;JDBC&quot;&gt;&lt;/transactionManager&gt;
        &lt;dataSource type=&quot;POOLED&quot;&gt;&lt;!--使用集成的连接池--&gt;
            &lt;property name=&quot;driver&quot; value=&quot;com.mysql.jdbc.Driver&quot;/&gt;
            &lt;property name=&quot;url&quot; value=&quot;JDBC:mysql://localhost:3306/bbs&quot;/&gt;
            &lt;property name=&quot;username&quot; value=&quot;root&quot;/&gt;
            &lt;property name=&quot;password&quot; value=&quot;root&quot;/&gt;
        &lt;/dataSource&gt;
    &lt;/environment&gt;
&lt;/environments&gt;

&lt;mappers&gt;

<!--                <package name="com.ljj.dao"/>-->

        <mapper resource="com/ljj/dao/ReplyMapper.xml"/>

<!--        <mapper class="com.ljj.dao.IReplyDao"/>-->

</mappers>
</configuration>

<?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.ljj.dao.IReplyDao"><!--一定要和接口类名一致-->

<!--下面的id和接口里的方法名一致-->

<resultMap id="getAllResultMapper" type="Post">

<id column="pId" property="id"/>

<result column="pTitle" property="title"/>

<result column="pContext" property="context"/>

<result column="pTime" property="time"/>

<result column="pUId" property="userId"/>

<result column="pUName" property="userName"/>

<collection property="replies" javaType="Reply">

<result column="rId" property="id"/>

<result column="rContext" property="context"/>

<result column="rTime" property="time"/>

<result column="rUId" property="userId"/>

<result column="rUName" property="userName"/>

</collection>

</resultMap>

<select id="getAll" parameterType="int" resultMap="getAllResultMapper">

SELECT

pId,

pTitle,

pContext,

pTime,

post.uId AS pUId,

pUser.uName AS pUName,

rId,

rContext,

rTime,

reply.uId AS rUId,

rUser.uName AS rUName

FROM

post

JOIN USER AS pUser ON post.uId = pUser.uId

JOIN reply USING ( pId )

JOIN USER AS rUser ON reply.uId = rUser.uId

WHERE

pId = #

ORDER BY

rTime

</select>
&lt;insert id=&quot;add&quot; parameterType=&quot;Reply&quot;&gt;&lt;!--这里员Dao返回的是boolean--&gt;
    &lt;selectKey resultType=&quot;int&quot; keyProperty=&quot;id&quot; order=&quot;AFTER&quot;&gt;
        select last_insert_id();
    &lt;/selectKey&gt;
    insert into reply values(null,#{context},#{time},#{userId},#{postId})
&lt;/insert&gt;

&lt;select id=&quot;getIdByTitle&quot; parameterType=&quot;String&quot; resultType=&quot;int&quot;&gt;
    select rId from reply where rTitle=#{title}
&lt;/select&gt;
&lt;delete id=&quot;delete&quot; parameterType=&quot;Reply&quot;&gt;
    &lt;!--    public boolean delete(int replyId, int postId, int userId, boolean isAdmin);--&gt;
    delete from reply where pId=#{postId} and rId=#{id}
&lt;/delete&gt;
&lt;update id=&quot;change&quot; parameterType=&quot;Reply&quot;&gt;
    &lt;!--    public boolean change(int replyId, int postId, int userId, String content);--&gt;
    update reply set rContext=#{context} where pId=#{postId} and rId=#{id}
&lt;/update&gt;

&lt;select id=&quot;getUserId&quot; parameterType=&quot;int&quot; resultType=&quot;int&quot;&gt;
    select uId from reply where rId=#{rId}
&lt;/select&gt;

</mapper>

public interface MyDao {
    public List<MyNew> getAll();
    public MyNew getOneById(int id);
    public List<MyNew> getAllByLikeCase(String value);
    public int insert(MyNew obj);
    public int update(MyNew obj);
    public int delete(String title);
}