MyBatis缓存

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本文介绍了MyBatis中的一级缓存和二级缓存配置方法，并提供了具体示例，包括如何启用缓存、配置Ehcache及自定义缓存实现。

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一：MyBatis的一级缓存默认是开启的，但是如果MyBatis和Spring搭配后，一级缓存失效，如果想用一级缓存，加上@Transactional就可以了。

二：二级缓存：

在mybatis.xml中加入<setting name="cacheEnabled" value="true" /> 在PersonDao.xml中加入<cache />

<?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="cacheEnabled" value="true" />
	</settings>
	<mappers>
		<mapper resource="com/we/dao/PersonDao.xml" />
	</mappers>
</configuration>

<?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.we.dao.PersonDao">
	<select id="get" parameterType="com.we.entry.Person" resultMap="result">
		select * from person WHERE id=#{id}
	</select>

	<resultMap type="com.we.entry.Person" id="result">
		<id column="id" property="id" />
		<result column="name" property="name" />
	</resultMap>

	<update id="updateById" parameterType="com.we.entry.Person">
		update person set
		name=#{name} where id=#{id}
	</update>
	<cache />
</mapper>

三：可以通过对比日志查看到缓存是否成功。如果不加<cache />和加则是以下两种

DEBUG 2016-08-29 20:08:09,499 org.mybatis.spring.SqlSessionUtils: Creating a new SqlSession
DEBUG 2016-08-29 20:08:09,499 org.mybatis.spring.SqlSessionUtils: SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@253d9f73] was not registered for synchronization because synchronization is not active
DEBUG 2016-08-29 20:08:09,499 org.apache.ibatis.cache.decorators.LoggingCache: Cache Hit Ratio [com.we.dao.PersonDao]: 0.75
DEBUG 2016-08-29 20:08:09,499 org.mybatis.spring.SqlSessionUtils: Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@253d9f73]

2
DEBUG 2016-08-29 20:05:25,212 org.mybatis.spring.SqlSessionUtils: Creating a new SqlSession
DEBUG 2016-08-29 20:05:25,212 org.mybatis.spring.SqlSessionUtils: SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@1941a8ff] was not registered for synchronization because synchronization is not active
DEBUG 2016-08-29 20:05:25,212 org.springframework.jdbc.datasource.DataSourceUtils: Fetching JDBC Connection from DataSource
DEBUG 2016-08-29 20:05:25,212 org.mybatis.spring.transaction.SpringManagedTransaction: JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@2e1ef60] will not be managed by Spring
DEBUG 2016-08-29 20:05:25,212 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Preparing: select * from person WHERE id=?
DEBUG 2016-08-29 20:05:25,212 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: 1(Integer)
DEBUG 2016-08-29 20:05:25,228 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <== Total: 1
DEBUG 2016-08-29 20:05:25,228 org.mybatis.spring.SqlSessionUtils: Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@1941a8ff]
DEBUG 2016-08-29 20:05:25,228 org.springframework.jdbc.datasource.DataSourceUtils: Returning JDBC Connection to DataSource
3

四配置Ehcache：加入jar包

<dependency>
<groupId>net.sf.ehcache</groupId>
<artifactId>ehcache-core</artifactId>
<version>2.6.11</version>
</dependency>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis-ehcache</artifactId>
<version>1.0.0</version>
</dependency>
然后把上面的cacha换成下面两个的任意一个。可以看一下两个类的实现就可以发现，LoggingEhcache是对EhcacheCache的包装。（LoggingEhcache的构造方法）
<cache type="org.mybatis.caches.ehcache.LoggingEhcache" />
<cache type="org.mybatis.caches.ehcache.EhcacheCache"/>