mybatis:一级缓存And二级缓存
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一级缓存,与hibernate一样,都是session缓存,也就是说该缓存的应用范围为同一个SqlSession.(不用废话)
二级缓存,mybatis自身也实现了缓存,但是mybatis的缓存实现并不同于我们常用的,这里介绍EhCache与MyBatis的整合。
默认的Mybatis缓存配置
只需要在mapper.xml中配置标签
<mapper namespace="com.xbz.user.mapper.UserMapper"> <cache type="org.mybatis.caches.ehcache.EhcacheCache"></cache> <select id="selectById" parameterType="java.lang.Long" resultType="com.xbz.user.entity.User"> SELECT * FROM users WHERE id = #{id} </select> </mapper>
test类
@Test public void testTwoLevelCache(){ User user1 = userMapper.selectById(1L); System.out.println("--------------------------------------------------------------------"); User user2 = userMapper.selectById(1L); System.out.println(user1==user2); }
测试结果
如下日志可看出,myabtis确实使用了二级缓存,没有查询两次数据库,但是两个user却是不相等的。
原因:首先mybatis的缓存的实体类,必须实现Serializable接口,另外估计他会将数据序列化查找二级缓存时再反序列化,反正了解就好,何必纠结
2016-09-26 20:29:39,464 org.mybatis.spring.transaction.SpringManagedTransaction.openConnection JDBC Connection [com.mchange.v2.c3p0.impl.NewProxyConnection@31148fb3] will be managed by Spring2016-09-26 20:29:39,474 com.xbz.user.mapper.UserMapper.selectById.debug ==> Preparing: SELECT * FROM users WHERE id = ? 2016-09-26 20:29:39,511 com.xbz.user.mapper.UserMapper.selectById.debug ==> Parameters: 1(Long)2016-09-26 20:29:39,542 com.xbz.user.mapper.UserMapper.selectById.debug <== Total: 12016-09-26 20:29:39,548 org.mybatis.spring.SqlSessionUtils.closeSqlSession Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@46603295]2016-09-26 20:29:39,549 org.mybatis.spring.SqlSessionUtils.beforeCompletion Transaction synchronization deregistering SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@46603295]2016-09-26 20:29:39,549 org.mybatis.spring.SqlSessionUtils.beforeCompletion Transaction synchronization closing SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@46603295]--------------------------------------------------------------------2016-09-26 20:29:39,557 org.mybatis.spring.SqlSessionUtils.getSqlSession Creating a new SqlSession2016-09-26 20:29:39,557 org.mybatis.spring.SqlSessionUtils.registerSessionHolder Registering transaction synchronization for SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7d230d96]2016-09-26 20:29:39,577 com.xbz.user.mapper.UserMapper.getObject Cache Hit Ratio [com.xbz.user.mapper.UserMapper]: 0.52016-09-26 20:29:39,578 org.mybatis.spring.SqlSessionUtils.closeSqlSession Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7d230d96]2016-09-26 20:29:39,578 org.mybatis.spring.SqlSessionUtils.beforeCompletion Transaction synchronization deregistering SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7d230d96]2016-09-26 20:29:39,578 org.mybatis.spring.SqlSessionUtils.beforeCompletion Transaction synchronization closing SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7d230d96]false
EhCache才是我们的重点
- 导入EhCache.jar
- 导入mybtatis-ehcache.jar
- org.mybatis.caches.ehcache.EhcacheCache
maven方式:
<dependency> <groupId>net.sf.ehcache</groupId> <artifactId>ehcache</artifactId> <version>2.10.2</version></dependency><dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis-ehcache</artifactId> <version>1.0.0</version></dependency>
然后再配置之前的Cache标签
<cache type="org.mybatis.caches.ehcache.EhcacheCache"></cache>
再来测试下结果(依旧是上面的测试方法)
哈哈哈,这次满意了吧!!!确实得到是同一个对象
2016-09-26 20:40:13,334 org.mybatis.spring.transaction.SpringManagedTransaction.openConnection JDBC Connection [com.mchange.v2.c3p0.impl.NewProxyConnection@20962ef0] will be managed by Spring2016-09-26 20:40:13,344 com.xbz.user.mapper.UserMapper.selectById.debug ==> Preparing: SELECT * FROM users WHERE id = ? 2016-09-26 20:40:13,380 com.xbz.user.mapper.UserMapper.selectById.debug ==> Parameters: 1(Long)2016-09-26 20:40:13,403 com.xbz.user.mapper.UserMapper.selectById.debug <== Total: 12016-09-26 20:40:13,409 org.mybatis.spring.SqlSessionUtils.closeSqlSession Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@504148d4]2016-09-26 20:40:13,409 org.mybatis.spring.SqlSessionUtils.beforeCompletion Transaction synchronization deregistering SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@504148d4]2016-09-26 20:40:13,410 org.mybatis.spring.SqlSessionUtils.beforeCompletion Transaction synchronization closing SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@504148d4]2016-09-26 20:40:13,412 net.sf.ehcache.store.disk.Segment.put put added 0 on heap--------------------------------------------------------------------2016-09-26 20:40:13,415 org.mybatis.spring.SqlSessionUtils.getSqlSession Creating a new SqlSession2016-09-26 20:40:13,415 org.mybatis.spring.SqlSessionUtils.registerSessionHolder Registering transaction synchronization for SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@249c5c4d]2016-09-26 20:40:13,415 com.xbz.user.mapper.UserMapper.getObject Cache Hit Ratio [com.xbz.user.mapper.UserMapper]: 0.52016-09-26 20:40:13,415 org.mybatis.spring.SqlSessionUtils.closeSqlSession Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@249c5c4d]2016-09-26 20:40:13,416 org.mybatis.spring.SqlSessionUtils.beforeCompletion Transaction synchronization deregistering SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@249c5c4d]2016-09-26 20:40:13,416 org.mybatis.spring.SqlSessionUtils.beforeCompletion Transaction synchronization closing SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@249c5c4d]true
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