mybatis一级二级缓存

柔情只为你懂 2022-03-21 03:54 321阅读 0赞

# mybatis一级二级缓存 #

### 文章目录 ###

*  mybatis一级二级缓存
 *   *  前言
     *  一、mybatis一级缓存
     *  二、mybatis二级缓存

--------------------

## 前言 ##

缓存在我们的日常开发中经常遇到，尤其在我们操作数据库时，要打开连接，操作数据库，操作完毕后要关闭，整个流程耗时，消耗性能。但是有了缓存机制，我们可以在打开连接之前就判断，是否有缓存，有缓存，则直接从缓存中读取，这样效率提升了数倍。  
mybatis缓存分为一级缓存和二级缓存，可以配置相关的设置。  
mybatis的一级缓存是相对于SqlSession定义，二级缓存相对于mapper来定义的。

## 一、mybatis一级缓存 ##

mybatis默认是支持一级缓存的，无需配置。  
这里我们测试一下，下面是我的测试代码

@Test
        public void testOne() {
            SqlSession mSession = null;
            ImsUser imsUser = null;
            ImsUser imsUser2 = null;
            try {
                mSession = SqlSessionUtils.getSqlSession(sqlSessionFactory);
                ImsUserMapper mapper = mSession.getMapper(ImsUserMapper.class);
                imsUser = mapper.findById("1");
                imsUser2 = mapper.findById("1");
                mSession.commit();
            } catch (Exception ex) {
                mSession.rollback();
            } finally {
                mSession.close();
            }
            if (imsUser != null) {
                System.out.println("user1");
                System.out.println(imsUser.toString());
            }
            if (imsUser2 != null) {
                System.out.println("user2");
                System.out.println(imsUser2.toString());
            }
        }

然后运行，可看到日志

[2019-01-30 14:19:27] [main] [DEBUG] [com.fm.mapper.ImsUserMapper:62] -- Cache Hit Ratio [com.fm.mapper.ImsUserMapper]: 0.0
    [2019-01-30 14:19:27] [main] [DEBUG] [com.fm.mapper.ImsUserMapper.findById:159] -- ==>  Preparing: SELECT * FROM todo_user WHERE id=? 
    [2019-01-30 14:19:27] [main] [DEBUG] [com.fm.mapper.ImsUserMapper.findById:159] -- ==> Parameters: 1(String)
    [2019-01-30 14:19:27] [main] [DEBUG] [com.fm.mapper.ImsUserMapper.findById:159] -- <==      Total: 1
    [2019-01-30 14:19:27] [main] [DEBUG] [com.fm.mapper.ImsUserMapper:62] -- Cache Hit Ratio [com.fm.mapper.ImsUserMapper]: 0.0
    user1
    ImsUser(id=1, name=方明, phone=13825123792, password=null, idcard=null, mail=null, createtime=Mon Aug 06 10:22:55 CST 2018)
    user2
    ImsUser(id=1, name=方明, phone=13825123792, password=null, idcard=null, mail=null, createtime=Mon Aug 06 10:22:55 CST 2018)

通过日志我们可以看到，我们的查询语句只执行了一次。如果不知道怎么设置mybatis的日志，可查看我之前的博文[springmvc、springboot使用logback查看myabtis日志][springmvc_springboot_logback_myabtis]

## 二、mybatis二级缓存 ##

我们使用同一个SqlSessionFactory，声明两个SqlSession来测试一下。  
1、在mybatis-config.xml的setting中配置cacheEnabled为ture，旧版本为false，新版本默认是true。

<?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>
            
            <setting name="logImpl" value="SLF4J" />
            
            <setting name="cacheEnabled" value="true"/>
        </settings>
    </configuration>

2、在mapper文件中加上

<?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.fm.mapper.ImsUserMapper">
        <cache/>
    
        
        <resultMap id="BaseResultMap" type="com.fm.entity.ImsUser">
            <id column="id" property="id" />
            <result column="name" property="name" />
            <result column="phone" property="phone" />
            <result column="password" property="password" />
            <result column="password" property="password" />
            <result column="idcard" property="idcard" />
            <result column="mail" property="mail" />
            <result column="createtime" property="createtime" />
        </resultMap>
    
        <select id="findById" resultType="com.fm.entity.ImsUser">
            SELECT * FROM todo_user WHERE id=#{userid}
        </select>
    
    </mapper>

3、测试一下，代码如下：

@Test
        public void testTwo() {
            SqlSession mSession1 = null;
            SqlSession mSession2 = null;
            ImsUser imsUser = null;
            ImsUser imsUser2 = null;
            mSession1 = SqlSessionUtils.getSqlSession(sqlSessionFactory);
            ImsUserMapper mapper = mSession1.getMapper(ImsUserMapper.class);
            imsUser = mapper.findById("1");
            mSession1.commit();
            mSession1.close();
            if (imsUser != null) {
                System.out.println("user1");
                System.out.println(imsUser.toString());
            }
    
            mSession2 = SqlSessionUtils.getSqlSession(sqlSessionFactory);
            ImsUserMapper mapper2 = mSession2.getMapper(ImsUserMapper.class);
            imsUser2 = mapper2.findById("1");
            mSession2.commit();
            mSession2.close();
            if (imsUser2 != null) {
                System.out.println("user2");
                System.out.println(imsUser2.toString());
            }
        }

运行代码，查看日志

[2019-01-30 14:47:54] [main] [DEBUG] [com.fm.mapper.ImsUserMapper:62] -- Cache Hit Ratio [com.fm.mapper.ImsUserMapper]: 0.0
    [2019-01-30 14:47:55] [main] [DEBUG] [com.fm.mapper.ImsUserMapper.findById:159] -- ==>  Preparing: SELECT * FROM todo_user WHERE id=? 
    [2019-01-30 14:47:55] [main] [DEBUG] [com.fm.mapper.ImsUserMapper.findById:159] -- ==> Parameters: 1(String)
    [2019-01-30 14:47:55] [main] [DEBUG] [com.fm.mapper.ImsUserMapper.findById:159] -- <==      Total: 1
    user1
    ImsUser(id=1, name=方明, phone=13825123792, password=null, idcard=null, mail=null, createtime=Mon Aug 06 10:22:55 CST 2018)
    [2019-01-30 14:47:55] [main] [DEBUG] [com.fm.mapper.ImsUserMapper:62] -- Cache Hit Ratio [com.fm.mapper.ImsUserMapper]: 0.5
    user2
    ImsUser(id=1, name=方明, phone=13825123792, password=null, idcard=null, mail=null, createtime=Mon Aug 06 10:22:55 CST 2018)

从日志可以看到，sql语句只执行了一次，第二次直接从缓存中获取的数据。

这里只做了简单的测试，关于myabtis的缓存，接下来我会再写一篇博文，进行深入解析。感谢关注。

[springmvc_springboot_logback_myabtis]: https://blog.csdn.net/u012489412/article/details/86691611