JBoss4.2.x中启用JPA二级缓存
JPA SPEC中没有定义关于一级、二级缓存的规范（事实上JCP对各JSR都很少定义涉及性能优化规范），要启用二级缓存需要使用JPA Provider专有的配置，JBoss(Hibernate)中配置如下。
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Specify the following code piece in persistence-unit.xml#/persistence-unit/properties/
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<property name="hibernate.cache.use_query_cache" value="true" /><property name="hibernate.cache.provider_class" value="org.hibernate.cache.HashtableCacheProvider" />
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Add an '@Cache' annatation to the entity class, and choose the right caching strategy.
import org.hibernate.annotations.Cache;import org.hibernate.annotations.CacheConcurrencyStrategy;?
@Cache(usage=CacheConcurrencyStrategy.READ_WRITE)?
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