【Mybatis学习总结八】Mybatis缓存

这节内容了解下即可。

如多数持久层框架一样，Mybatis同样提供了一级缓存和二级缓存。

（*）一级缓存：

(1)一级缓存也就是Session级的缓存，默认是开启的，查询操作是使用缓存的；

(2)必须是同一个session,session.close()后就不能使用了；

(3)查询条件不一致时不会使用缓存；

(4)清理缓存完了后session.clearCache()，不会使用；

(5)实际上执行增删改CUD操作，会自动刷新缓存，也就是不会使用缓存；

(*)二级缓存：

(1)要在.xml文件中加入<cache/>；

(2)实体类必须实现implements Serializable

1 准备数据表和数据

CREATE TABLE c_user(
id INT PRIMARY KEY AUTO_INCREMENT,
NAME VARCHAR(20),
age INT
);
INSERT INTO c_user(NAME, age) VALUES('Tom', 12);
INSERT INTO c_user(NAME, age) VALUES('Jack', 11);

2 创建表实体 CUser

public class User implements Serializable{
     private int id;
     private String name;
     private int age;
}

3

<?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.atguigu.mybatis.test8.userMapper">
<select id="getUser" parameterType="int" resultType="_CUser">
select * from c_user where id=#{id}
</select>
<update id="updateUser" parameterType="_CUser">
update c_user set
name=#{name}, age=#{age} where id=#{id}
</update>
</mapper>

4 注册
5 测试

package com.mybatis.test8;

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

import com.mybatis.entities.CUser;

public class Test8 {

  /**
   * 测试一级缓存
   */
  @Test
  public void test() {

    SqlSession session= MybatisUtils.getSqlSessionFactory().openSession();
    String statement = "com.mybatis.test8.cuserMapper4.getUser";
    
    CUser user  =session.selectOne(statement, 2);
    System.out.println("***"+user);
    
    //1 查询条件相同，参数相同，直接使用缓存
    user  =session.selectOne(statement, 1);
    System.out.println(user);

    //2 查询条件相同，参数不同，不会使用缓存
    user  =session.selectOne(statement, 2);
    System.out.println(user);
    
    //3执行session关闭
    //session.close();
    SqlSession session3= MybatisUtils.getSqlSessionFactory().openSession();
    user  =session3.selectOne(statement, 2);
    System.out.println("3:"+user);
    //4清理缓存后
    session3.clearCache();
    user  =session.selectOne(statement, 2);
    System.out.println("4:"+user);
    
    //5 session不同,不使用缓存
    SqlSession session5= MybatisUtils.getSqlSessionFactory().openSession();
    user  =session5.selectOne(statement, 1);
    System.out.println("6:"+user);
    
    session.close();
    
  
  }
  
  @Test
  public void update(){
    //执行更新
    SqlSession session6= MybatisUtils.getSqlSessionFactory().openSession();
    String statement = "com.mybatis.test8.cuserMapper4.updateUser";
    session6.update(statement, new CUser(2,"user",23));
    
    statement = "com.mybatis.test8.cuserMapper4.getUser";
    
    CUser user  =session6.selectOne(statement, 2);
    System.out.println("***"+user);
  }
}

package com.mybatis.test8;

import static org.junit.Assert.*;

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

import com.mybatis.entities.CUser;

public class Test8_2 {

  /**
   * 测试二级缓存
   */
  @Test
  public void test2() {
    SqlSession session= MybatisUtils.getSqlSessionFactory().openSession();
    SqlSession session2= MybatisUtils.getSqlSessionFactory().openSession();
    
    String statement = "com.mybatis.test8.cuserMapper4.getUser";
    CUser user  =session.selectOne(statement,1);
    session.commit();
    System.out.println("1:"+user);
    
    user  =session2.selectOne(statement, 1);
    session2.commit();
    System.out.println("2:"+user);
  }

}