Hibernate JPA 中配置Ehcache二级缓存
在Hibernate3 JPA里配置了一下非分布式环境的二级缓存，效果不错。具体过程如下：
?
1， 需要引入的jar包
????? http://ehcache.org/downloads/catalog?下载的包里已经包含了简单的例子和javadoc
?
????? ehcache-core-2.4.6.jar （必需）
????? ehcache-terracotta-2.4.6.jar （必需）
????? slf4j-api-1.6.1.jar
????? slf4j-jdk14-1.6.1.jar
?
?
2， 在JPA的persistence.xml中加入以下配置
?
????? <property name="hibernate.cache.provider_class"?
??????????????? value="org.hibernate.cache.SingletonEhCacheProvider" />
? ???<property name="hibernate.cache.provider_configuration" value="/ehcache.xml" />
? ???<property name="hibernate.cache.use_second_level_cache" value="true" />
? ???<property name="hibernate.cache.use_query_cache" value="true" />
?
?
3， 对ehcache进行简单的设置（ehcache.xml）
????? <?xml version="1.0" encoding="UTF-8"?>
????? <ehcache>
????? <defaultCache maxElementsInMemory="1000" eternal="false"
????????? ?timeToIdleSeconds="1200" timeToLiveSeconds="1200" overflowToDisk="false"
?????????? clearOnFlush="true">
????? </defaultCache>
?????? <!-- 单独对某个entity的缓存策略设置-->
????? <cache name="com.payment.entity.PromotionEntity" maxElementsInMemory="100"
?????????? eternal="false"
????????? ?timeToIdleSeconds="1200" timeToLiveSeconds="1200" overflowToDisk="false"
?????????? clearOnFlush="true">
????? </cache>
???? </ehcache>
?
?
4， JPA的Entity类中声明缓存的隔离机制
?
?????? import org.hibernate.annotations.Cache;
?????? import org.hibernate.annotations.CacheConcurrencyStrategy;
?
??????@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
????? @Entity
????? @Table(name = "catagory")
????? public class CatagoryEntity extends BaseEntity { ... }
?
?
5， 如何使用二级缓存中的对象
?????? 在Hibernate中可以通过org.hibernate.Query.setCacheable(true);
?????? 在JPA中，由于EntityManager中得到的javax.persistence.Query没有这个方法了。我们可以通过
?????? javax.persistence.Query.setHint(”org.hibernate.cacheable”, true);来实现读取二级缓存。
?
?
?
6， 在log4j输出日志中可以看到缓存机制作用
?
????? 18:05:30,682 DEBUG SessionImpl:265 - opened session at timestamp: 5410486397673472
????? 18:05:30,682 DEBUG StandardQueryCache:125 - checking cached query results in region:?????
????????? org.hibernate.cache.StandardQueryCache
????? 18:05:30,682 DEBUG EhCache:74 - key: sql: select promotione0_.id as id2_,?
????????? promotione0_.catagory_id as catagory6_2_, promotione0_.description as descript2_2_,?
????????? promotione0_.enabled as enabled2_, promotione0_.name as name2_, promotione0_.picture as
????????? picture2_, promotione0_.product_id as product7_2_ from promotion promotione0_; parameters:
????????? ; named parameters: {}
????? 18:05:30,682 DEBUG StandardQueryCache:183 - Checking query spaces for up-to-dateness:
????????? [promotion]
????? 18:05:30,682 DEBUG EhCache:74 - key: promotion
????? 18:05:30,682 DEBUG EhCache:83 - Element for promotion is null
????? 18:05:30,682 DEBUG StandardQueryCache:140 - returning cached query results
????? 18:05:30,714 DEBUG EhCache:74 - key: com.payment.entity.PromotionEntity#1
????? 18:05:30,714 DEBUG StatefulPersistenceContext:893 - initializing non-lazy collections
????? 18:05:30,714 DEBUG EhCache:74 - key: com.payment.entity.PromotionEntity#2
????? 18:05:30,714 DEBUG StatefulPersistenceContext:893 - initializing non-lazy collections
????? 18:05:30,714 DEBUG EhCache:74 - key: com.payment.entity.PromotionEntity#3
????? 18:05:30,714 DEBUG StatefulPersistenceContext:893 - initializing non-lazy collections
????? 18:05:30,714 DEBUG EhCache:74 - key: com.payment.entity.PromotionEntity#4
????? 18:05:30,714 DEBUG StatefulPersistenceContext:893 - initializing non-lazy collections
????? 18:05:30,714 DEBUG EhCache:74 - key: com.payment.entity.PromotionEntity#5
?
?
