import java.util.LinkedHashMap;import java.util.List;import java.util.Map;import org.apache.ibatis.session.SqlSession;import cn.itcast.javaee.mybatis.util.MybatisUtil;/** * 持久层  * @author AdminTC */public class StudentDao {    /**     * 有条件的查询所有学生     */    public List<Student> findAll(Integer id,String name,Double sal) throws Exception{        SqlSession sqlSession = null;        try{            sqlSession = MybatisUtil.getSqlSession();            Map<String,Object> map = new LinkedHashMap<String,Object>();            map.put("pid",id);            map.put("pname",name);            map.put("psal",sal);            return sqlSession.selectList("studentNamespace.findAll",map);        }catch(Exception e){            e.printStackTrace();            throw e;        }finally{            MybatisUtil.closeSqlSession();        }    }    public static void main(String[] args) throws Exception{        StudentDao dao = new StudentDao();        List<Student> studentList = dao.findAll(5,"哈哈",7000D);        for(Student s : studentList){            System.out.println(s.getId()+":"+s.getName()+":"+s.getSal());        }    }}

<?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="studentNamespace">       <resultMap type="cn.itcast.javaee.mybatis.app11.Student" id="studentMap">        <id property="id" column="students_id"/>        <result property="name" column="students_name"/>        <result property="sal" column="students_sal"/>    </resultMap>    <select id="findAll" parameterType="map" resultMap="studentMap">        select * from students        <where>            <if test="pid!=null">                and students_id = #{pid}            </if>            <if test="pname!=null">                and students_name = #{pname}            </if>            <if test="psal!=null">                and students_sal = #{psal}            </if>        </where>    </select></mapper>