public interface StudentDao {
    /**
     *  验证mybatis2级缓存！
     */
    Student selectStudentById(Integer sId);
    
}

<?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="cn.bdqn.dao.StudentDao">
  <cache/> <!-- 配置2级缓存 -->
     <select id="selectStudentById" resultType="Student">
      select  sid,sname from  student where sid=#{xxx}
    </select>
    
</mapper>

/**
 *学生对应的实体类
 */
public class Student  implements Serializable {
    
    private  Integer sId;
    private  String sName;

    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 Student(Integer sId, String sName) {
        super();
        this.sId = sId;
        this.sName = sName;
    }
    public Student() {
        super();
    }
    @Override
    public String toString() {
        return "Student [sId=" + sId + ", sName=" + sName +"]";
    }
    

}

package cn.bdqn.test;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.ibatis.session.SqlSession;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import cn.bdqn.bean.Student;
import cn.bdqn.dao.StudentDao;
import cn.bdqn.util.SessionUtil;

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();
        }
    }

/**
 * 验证2级缓存
 * 
 * 开启内置2级缓存的步骤
 * 01.实体类对象 要实现serializable 序列化接口
 * 02.在mapper文件中 增加  <cache/>节点
 */
    @Test
    public void test1() {
        Student student = dao.selectStudentById(1);
        System.out.println(student);
        
        session.close(); //关闭了session   一级缓存中的数据肯定清空了
        
        session = SessionUtil.getSession();  //再次获取session 查询数据
        dao = session.getMapper(StudentDao.class);
        //这时候不会再有sql语句了  因为2级缓存中存在相同的查询（mapper文件中sql的id）和相同的sql语句
        Student student2 = dao.selectStudentById(1);
        System.out.println(student2);
    }
    
}

public interface StudentDao {
    /**
     *  验证mybatis2级缓存！
     */
    Student selectStudentById(Integer sId);
    
    /**
     * 验证增删改查对2级缓存的影响！
     */
    void addStudent(Student student);
}

<?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="cn.bdqn.dao.StudentDao">
  <cache/> <!-- 配置2级缓存 -->
     <select id="selectStudentById" resultType="Student">
      select  sid,sname from  student where sid=#{xxx}
    </select>
    
    <!-- 新增一个学生   验证对2级缓存的影响 -->
    <insert id="addStudent">
      insert into student values(#{sId},#{sName})
      <!--#{sId},#{sName} 对应的是实体类中的属性  -->
    </insert>
    
</mapper>

    /**
     * 验证增删改对2级缓存的影响
     */
    @Test
    public void test2() {
        Student student = dao.selectStudentById(1);
        System.out.println(student);
        
        session.close(); //关闭了session   一级缓存中的数据肯定清空了
        
        session = SessionUtil.getSession();  //再次获取session 查询数据
        dao = session.getMapper(StudentDao.class);
        //新增学生信息  看看对2级缓存的影响
        dao.addStudent(new Student(66,"测试"));
        
        Student student2 = dao.selectStudentById(1);
        System.out.println(student2);
    }