/** *学生对应的实体类 */public class Student {        private  Integer sId;    private  String sName;    //一个学生可以有多个老师    private Set<Teacher> teachers=new HashSet<Teacher>();        public Integer getsId() {        return sId;    }    public void setsId(Integer sId) {        this.sId = sId;    }    public String getsName() {        return sName;    }    public void setsName(String sName) {        this.sName = sName;    }    public Set<Teacher> getTeachers() {        return teachers;    }    public void setTeachers(Set<Teacher> teachers) {        this.teachers = teachers;    }    public Student(Integer sId, String sName, Set<Teacher> teachers) {        super();        this.sId = sId;        this.sName = sName;        this.teachers = teachers;    }    public Student() {        super();    }    //在双向关联的时候    只能一方显示关联信息   否则会出现stackOverflow 异常    @Override    public String toString() {        return "Student [sId=" + sId + ", sName=" + sName + ", teachers="                + teachers + "]";    }    }

/** *老师的实体类 */public class Teacher {    private  Integer tId;    private  String tName;     //一个老师可以有多个学生    private  Set<Student> students=new HashSet<Student>();    public Integer gettId() {        return tId;    }    public void settId(Integer tId) {        this.tId = tId;    }    public String gettName() {        return tName;    }    public void settName(String tName) {        this.tName = tName;    }    public Set<Student> getStudents() {        return students;    }    public void setStudents(Set<Student> students) {        this.students = students;    }    public Teacher(Integer tId, String tName, Set<Student> students) {        super();        this.tId = tId;        this.tName = tName;        this.students = students;    }    public Teacher() {        super();    }    @Override    public String toString() {        return "Teacher [tId=" + tId + ", tName=" + tName + ", students="                + students.size() + "]";    }    }

public interface StudentDao {    /**     * 根据学生的编号查询所有对应老师信息     */    Student selectTeahcerById(Integer tId);}

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-Mapper.dtd"><mapper namespace="cn.bdqn.dao.StudentDao">    <resultMap type="Student" id="studentMap">          <id property="sId" column="sid"/>          <result property="sName" column="sname"/>      <!-- 设置关联集合的属性  -->      <collection property="teachers" ofType="Teacher">          <id property="tId" column="tid"/>          <result property="tName" column="tname"/>      </collection>    </resultMap>     <!-- 根据学生的编号查询所有对应老师信息 -->     <select id="selectTeahcerById" resultMap="studentMap">      select  sid,sname,tid,tname from  student,middle,teacher         where  sid=studentId and tid=teacherId and sid=#{xxx}    </select>    </mapper>

 <!-- 加载映射文件信息 -->    <mappers>        <mapper resource="cn/bdqn/dao/StudentMapper.xml" />    </mappers>

public class TeacherTest {    StudentDao dao;    SqlSession session;    @Before    public void before() {        // 因为需要关闭session 需要把session提取出去        session = SessionUtil.getSession();        dao = session.getMapper(StudentDao.class);    }    @After    public void after() {        if (session != null) {            session.close();        }    }    /**     * 根据老师的编号查询所有的导师信息     */    @Test    public void test1() {        Student student = dao.selectTeahcerById(1);        System.out.println(student);    }    }