package com.abc.domain;
public class Teacher{
private int id;
private String name;  //姓名
private String gender;//性别
private String researchArea;//研究方向
private String title;//职称
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public String getResearchArea() {
return researchArea;
}
public void setResearchArea(String researchArea) {
this.researchArea = researchArea;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
}

/*数据库编码UTF8，以下命令是为了在脚本和
命令行中支持中文*/
set names gbk;
/*切换到courseman数据库*/
use courseman;
/*创建成绩表*/
drop table if exists teacher;
CREATE TABLE teacher(
id int NOT NULL AUTO_INCREMENT primarykey,
name varchar(10) NOT NULL,/*姓名*/
gender char(1) NOT NULL,/*性别*/
research_area varchar(20) NOT NULL,/*研究方向*/
title varchar(6) NOT NULL/*职称*/
);
/*添加第一条记录，自动生成的ID为1*/
insert into teacher(name,gender,research_area, title)
values('张伟','男','软件工程','讲师');

private Teacher supervisor; //指导教师

/*切换到courseman数据库*/
use courseman;
/*为学生表添加指导老师ID列*/
alter TABLE student add supervisor_id int not null
references teacher(id);
/*把上面新增的教师作为目前学生的指导教师*/
update student set supervisor_id=1;

<typeAliases>
<typeAlias alias="Student" type="com.abc.domain.Student"/>
<!--增加的教师类型别名-->
<typeAlias alias="Teacher" type="com.abc.domain.Teacher"/>
</typeAliases>

<select id="getById" parameterType="int" resultMap="studentResultMap">
select st.id,st.name,st.gender,
st.major,st.grade,
<!--为教师的id取别名，避免MyBatis向教师实体注入
此属性时与学生id混淆。以下的name和gender等属性
也是如此-->
t.id t_id,t.name t_name,t.gender t_gender,
t.title,t.research_area
from student st, teacher t
where st.supervisor_id = t.id
and st.id=#{id}
</select>

<resultMap id="studentResultMap" type="Student">
<!--普通属性映射与以前一致-->
<id property="id" column="id"/>
<result property="name" column="name"/>
<result property="gender" column="gender"/>
<result property="major"  column="major"/>
<result property="grade"  column="grade"/>
<!--property="supervisor"表明这是为了映射学生实体的
supervisor属性。javaType="Teacher"用到了Teacher这个
别名定义，并指出了supervisor属性的java类型-->
<association property="supervisor" javaType="Teacher">
<!--教师自身的属性与数据库字段的映射。注意这里用到了字段别名--><id property="id" column="t_id"/><result property="name" column="t_name"/><result property="gender" column="t_gender"/><result property="researchArea" column="research_area"/><result property="title" column="title"/>
</association>
</resultMap>

package com.demo;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSession;
import com.abc.mapper.StudentMapper;
import com.abc.domain.Student;
import com.util.SqlSessionFactoryGen;
public class AssociationDemo
{
//获取SqlSessionFactory实例
private static SqlSessionFactory factory
= SqlSessionFactoryGen.getSqlSessionFactory();
public static void main(String[] args)
{
SqlSession session = factory.openSession();
StudentMapper mapper =
session.getMapper(StudentMapper.class);
//笔者的数据库中只有ID为4的学生。读者若运行此程序，
//须使用你的数据库中存在的学生ID。否则报空指针异常
Student student = mapper.getById(4);
//使用StringBuilder的append操作代替字符串的“+”
//操作可提高执行效率
StringBuilder sb = new StringBuilder("学生信息：\n");
sb.append("姓名：");
sb.append(student.getName());
sb.append(" ");
sb.append( "专业：");
sb.append(student.getMajor());
sb.append(" 年级：");
sb.append(student.getGrade());
sb.append("\n");
sb.append("指导教师信息：\n");
sb.append("姓名：");
sb.append(student.getSupervisor().getName());
sb.append(" ");
sb.append("职称：");
sb.append(student.getSupervisor().getTitle());
sb.append(" ");
sb.append("研究方向：");
sb.append(student.getSupervisor().getResearchArea());
System.out.println(sb.toString());
session.close();
}
}

<target name="run" depends="compile">
<!--指定AssociationDemo为要运行的类-->
<java fork="true" classname="com.demo.AssociationDemo" classpathref="library"><classpath path="${targetdir}"/>
</java>
</target>