Mybatis快速上手7、8 一级缓存和二级缓存

最新推荐文章于 2025-03-11 10:44:56 发布

执力

最新推荐文章于 2025-03-11 10:44:56 发布

阅读量295

点赞数

分类专栏： Mybatis快速上手文章标签： mybatis mysql jdbc java eclipse

本文链接：https://blog.youkuaiyun.com/XIMAX/article/details/106254303

版权

Mybatis快速上手专栏收录该内容

8 篇文章

订阅专栏

一级缓存和二级缓存

环境：Eclipse+Tomcat9+JDK10+Mybatis-3.1.1、Navicat
一级缓存
二级缓存

其他章节及开发包：https://blog.youkuaiyun.com/XIMAX/article/details/106255196

环境：Eclipse+Tomcat9+JDK10+Mybatis-3.1.1、Navicat

一级缓存

一级缓存默认是开启的
一级缓存存储作用域为 Session，当 Session flush 或 close 之后，该Session中的所有 Cache 就将清空。
一级缓存是SqlSession级别的缓存，缓存数据存储在HashMap中，在进行第一次查询时，首先会从数据库中查询出结果，然后将结果存在一级缓存中；当我们第二次查询时，首先会查询一级缓存，如果一级缓存没有，再查询数据库。在进行CUD操作并执行了commit或关闭Sqlsession后会将缓存清空。
-----------------------------------------------------------分割线----------------------------------------------------------------

一级缓存较为简单，不做代码赘述，看一个简单案例

@Test
 void test() throws IOException {
  SqlSessionFactory factory = MybatisUtils.getFactory();
  SqlSession session = factory.openSession();

  String statement = "com.rjxy.test7.userMapper.getUser";
  
  CUser user = session.selectOne(statement,1);
  System.out.println(user);

  user = session.selectOne(statement,1);
  System.out.println(user);
  
  System.out.println("--------------");
  
  //清理掉则不会用一级缓存
  session.clearCache();
  user = session.selectOne(statement,1);
  System.out.println(user);

  System.out.println("---------------");
  
  //关闭后再打开，不是同一session对象，不会用一级缓存
  session.close();
  session = factory.openSession();
  
  user = session.selectOne(statement,1);
  System.out.println(user);
  session.close();
  }

结果输出：

2020-05-21 12:25:00,968 [main] DEBUG [com.rjxy.test7.userMapper.getUser] - ooo Using Connection [com.mysql.cj.jdbc.ConnectionImpl@4fbda97b]
2020-05-21 12:25:00,969 [main] DEBUG [com.rjxy.test7.userMapper.getUser] - ==>  Preparing: select * from c_user where id=? 
2020-05-21 12:25:01,031 [main] DEBUG [com.rjxy.test7.userMapper.getUser] - ==> Parameters: 1(Integer)
CUser [id=1, name=Tom, age=12]
CUser [id=1, name=Tom, age=12]
--------------
2020-05-21 12:25:01,163 [main] DEBUG [com.rjxy.test7.userMapper.getUser] - ooo Using Connection [com.mysql.cj.jdbc.ConnectionImpl@4fbda97b]
2020-05-21 12:25:01,163 [main] DEBUG [com.rjxy.test7.userMapper.getUser] - ==>  Preparing: select * from c_user where id=? 
2020-05-21 12:25:01,163 [main] DEBUG [com.rjxy.test7.userMapper.getUser] - ==> Parameters: 1(Integer)
CUser [id=1, name=Tom, age=12]
---------------
2020-05-21 12:25:01,167 [main] DEBUG [com.rjxy.test7.userMapper.getUser] - ooo Using Connection [com.mysql.cj.jdbc.ConnectionImpl@4fbda97b]
2020-05-21 12:25:01,167 [main] DEBUG [com.rjxy.test7.userMapper.getUser] - ==>  Preparing: select * from c_user where id=? 
2020-05-21 12:25:01,168 [main] DEBUG [com.rjxy.test7.userMapper.getUser] - ==> Parameters: 1(Integer)
CUser [id=1, name=Tom, age=12]

从结果中可以看出第一部分中，当同一session第二次查询相同内容时，没有再调用sql语句，而是直接从缓存中取出，清理掉缓存及关闭session再打开查询时又重新调用了sql语句，无法共享

二级缓存

二级缓存存储作用域为 Mapper(Namespace)，并且可自定义存储源，如 Ehcache
二级缓存是Mapper级别的缓存，拥有多个SqlSession，同一Mapper中每个SqlSession中的缓存内容共享。若要使用二级缓存则存储数据的Java类需要实现Serializable接口。
在进行CUD操作并执行了commit，缓存会被清空，默认不开启，开启需要在配置文件userMapper.xml中设置“”

在这里插入图片描述
test1~8分别对应八章，本章使用包test8、tool，文件config.xml、db.properties、log4j.properties

代码

建库，建表

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);

config.xml

<?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>
  <properties resource="db.properties"></properties>

<settings>
  <setting name="cacheEnabled" value="true"/>
 </settings>
 
  <typeAliases>
    <package name="com.rjxy.test8"/>
 <typeAliases>
 
 <typeAliases>
   <package name="com.rjxy.test2"/>
 <typeAliases>
 <environments default="development">
   <environment id="development">
    <transactionManager type="JDBC" />
    <dataSource type="POOLED">
     <property name="driver" value="${driver}" />
     <property name="url" value="${url}" />
     <property name="username" value="${username}" />
     <property name="password" value="${password}" />
    </dataSource>
   </environment>
  </environments>  
 
 <mappers>
   <mapper resource="com/rjxy/test8/userMapper.xml"/>
 <mappers>
</configuration>

userMapper8.xml

<?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.rjxy.test8.userMapper8">
 <cache></cache>
 <select id="getUser" parameterType="int" resultType="CUser2">
  select * from c_user where id=#{id}
 </select>
 <update id="updateUser" parameterType="CUser2">
  update c_user set name=#{name},age=#{age} where id=#{id}
 </update>
</mapper>

CUser2.java

package com.rjxy.test8;
import java.io.Serializable;
public class CUser2 implements Serializable{
private static final long serialVersionUID = 1L;
//二级缓存需要实现序列化接口
 private int id;
 private String name;
 private int age;

public CUser2() {}
 public CUser2(int id,String name,int age) {
  this.id = id;
  this.name = name;
  this.age = age;
 }
 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 int getAge() {
  return age;
 }
 public void setAge(int age) {
  this.age = age;
 }
 @Override
 public String toString() {
  return "CUser [id=" + id + ", name=" + name + ", age=" + age + "]";
 }
 }

JTest8.java

package com.rjxy.test8;

import java.io.IOException;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.junit.jupiter.api.Test;
class JTest8 {
@Test
 void test2() throws IOException {
  SqlSessionFactory factory = MybatisUtils.getFactory();
  SqlSession session1 = factory.openSession();
  SqlSession session2 = factory.openSession();

  String statement = "com.rjxy.test8.userMapper8.getUser";
  
  CUser2 user = session1.selectOne(statement,1);
  session1.commit();
  System.out.println(user);

  CUser2 user2 = session2.selectOne(statement,1);
  session2.commit();
  System.out.println(user2);
 }
}

其它

其它文件与该系列第一篇相同链接： https://blog.youkuaiyun.com/XIMAX/article/details/106244701

输出结果

2020-05-21 13:14:02,992 [main] DEBUG [com.rjxy.test8.userMapper8.getUser] - ooo Using Connection [com.mysql.cj.jdbc.ConnectionImpl@4fbda97b]
2020-05-21 13:14:02,993 [main] DEBUG [com.rjxy.test8.userMapper8.getUser] - ==>  Preparing: select * from c_user where id=? 
2020-05-21 13:14:03,098 [main] DEBUG [com.rjxy.test8.userMapper8.getUser] - ==> Parameters: 1(Integer)
CUser [id=1, name=Tom, age=12]
CUser [id=1, name=Tom, age=12]

可以看出，第二次查询与第一次查询所用的是同一个mapper文件下不同的session，但第二次查询没有调用sql语句