package com.yihaomen.mybatis.model;

import com.yihaomen.mybatis.enums.Gender;

import java.io.Serializable;

import java.util.List;

/**

 *  @ProjectName: springmvc-mybatis 

 */

public class Student implements Serializable{

    private static final long serialVersionUID = 735655488285535299L;

    private String id;

    private String name;

    private int age;

    private Gender gender;

    private List<Teacher> teachers;

    setters&getters()....;

    toString();

}

<?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.yihaomen.mybatis.dao.StudentMapper">

    <!--开启本mapper的namespace下的二级缓存-->

    <!--

        eviction:代表的是缓存回收策略，目前MyBatis提供以下策略。

        (1) LRU,最近最少使用的，一处最长时间不用的对象

        (2) FIFO,先进先出，按对象进入缓存的顺序来移除他们

        (3) SOFT,软引用，移除基于垃圾回收器状态和软引用规则的对象

        (4) WEAK,弱引用，更积极的移除基于垃圾收集器状态和弱引用规则的对象。这里采用的是LRU，

                移除最长时间不用的对形象

        flushInterval:刷新间隔时间，单位为毫秒，这里配置的是100秒刷新，如果你不配置它，那么当

        SQL被执行的时候才会去刷新缓存。

        size:引用数目，一个正整数，代表缓存最多可以存储多少个对象，不宜设置过大。设置过大会导致内存溢出。

        这里配置的是1024个对象

        readOnly:只读，意味着缓存数据只能读取而不能修改，这样设置的好处是我们可以快速读取缓存，缺点是我们没有

        办法修改缓存，他的默认值是false，不允许我们修改

    -->

    <cache eviction="LRU" flushInterval="100000" readOnly="true" size="1024"/>

    <resultMap id="studentMap" type="Student">

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

        <result property="name" column="name" />

        <result property="age" column="age" />

        <result property="gender" column="gender" typeHandler="org.apache.ibatis.type.EnumOrdinalTypeHandler" />

    </resultMap>

    <resultMap id="collectionMap" type="Student" extends="studentMap">

        <collection property="teachers" ofType="Teacher">

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

            <result property="name" column="tname"/>

            <result property="gender" column="tgender" typeHandler="org.apache.ibatis.type.EnumOrdinalTypeHandler"/>

            <result property="subject" column="tsubject" typeHandler="org.apache.ibatis.type.EnumTypeHandler"/>

            <result property="degree" column="tdegree" javaType="string" jdbcType="VARCHAR"/>

        </collection>

    </resultMap>

    <select id="selectStudents" resultMap="collectionMap">

        SELECT

            s.id, s.name, s.gender, t.id teach_id, t.name tname, t.gender tgender, t.subject tsubject, t.degree tdegree

        FROM

            student s

        LEFT JOIN

            stu_teach_rel str

        ON

            s.id = str.stu_id

        LEFT JOIN

            teacher t

        ON

            t.id = str.teach_id

    </select>

    <!--可以通过设置useCache来规定这个sql是否开启缓存，ture是开启，false是关闭-->

    <select id="selectAllStudents" resultMap="studentMap" useCache="true">

        SELECT id, name, age FROM student

    </select>

    <!--刷新二级缓存

    <select id="selectAllStudents" resultMap="studentMap" flushCache="true">

        SELECT id, name, age FROM student

    </select>

    -->

</mapper>

<?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>

    <settings>

        <!--这个配置使全局的映射器(二级缓存)启用或禁用缓存-->

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

        .....

    </settings>

    ....

</configuration>

package com.yihaomen.service.student;

import com.yihaomen.mybatis.dao.StudentMapper;

import com.yihaomen.mybatis.model.Student;

import com.yihaomen.mybatis.model.Teacher;

import com.yihaomen.service.BaseTest;

import org.apache.ibatis.session.SqlSession;

import org.apache.ibatis.session.SqlSessionFactory;

import java.util.List;

/**

 *   

 *  @ProjectName: springmvc-mybatis 

 */

public class TestStudent extends BaseTest {

    public static void selectAllStudent() {

        SqlSessionFactory sqlSessionFactory = getSession();

        SqlSession session = sqlSessionFactory.openSession();

        StudentMapper mapper = session.getMapper(StudentMapper.class);

        List<Student> list = mapper.selectAllStudents();

        System.out.println(list);

        System.out.println("第二次执行");

        List<Student> list2 = mapper.selectAllStudents();

        System.out.println(list2);

        session.commit();

        System.out.println("二级缓存观测点");

        SqlSession session2 = sqlSessionFactory.openSession();

        StudentMapper mapper2 = session2.getMapper(StudentMapper.class);

        List<Student> list3 = mapper2.selectAllStudents();

        System.out.println(list3);

        System.out.println("第二次执行");

        List<Student> list4 = mapper2.selectAllStudents();

        System.out.println(list4);

        session2.commit();

    }

    public static void main(String[] args) {

        selectAllStudent();

    }

}