I am using Hibernate 3.2 with JPA and using EhCache as a second level cache. Though, second level cache is working, e.g. when I turn the debugging on, I see messages like:
[java] 2007-08-01 14:52:54,449 [ReadWriteCache] Caching: com.amazon.otb.model.DataElement#10000
[java] 2007-08-01 14:52:54,449 [ReadWriteCache] Item was already cached: com.amazon.otb.model.DataElement#10000


However, I noticed that the objects that are being returned are not the same. I would like Hibernate to return the same object if it's in second level cache.

Here is how I am defining caching policies on my object:

@Entity
@Table(name="OTB_DATA_ELEMENTS")
@BatchSize(size=500)
@Cache(usage = CacheConcurrencyStrategy.READ_ONLY)
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class DataElement extends BaseEntity {


and my persistence.xml looks like:

<persistence-unit name="otb" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<class>com.amazon.otb.model.DataElement</class>
<properties>
<property name="hibernate.c3p0.min_size" value="2"/>
<property name="hibernate.c3p0.max_size" value="15"/>
<property name="hibernate.c3p0.timeout" value="150"/>
<property name="hibernate.c3p0.max_statements" value="500"/>
<property name="hibernate.c3p0.idle_test_period" value="600"/>
<property name="c3p0.acquire_increment" value="2"/>

<property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
<property name="hibernate.cache.use_second_level_cache" value="true"/>
<property name="hibernate.cache.use_minimal_puts" value="false"/>
<property name="hibernate.cache.use_query_cache" value="true"/>
<property name="hibernate.cache.use_structured_entries" value="true"/>

<property name= "hibernate.ejb.classcache.com.amazon.otb.model.DataElement" value="read-write"/>
<property name="hibernate.cache.provider_class" value="net.sf.ehcache.hibernate.SingletonEhCacheProvider"/
<property name="hibernate.generate_statistics" value="true"/>

<property name="hibernate.cache.provider_configuration" value="/com/amazon/otb/dao/ehcache.cfg.xml"/>

</properties>
</persistence-unit>




and ehcache.cfg.xml looks like

<?xml version="1.0" encoding="UTF-8"?>
<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="ehcache.xsd">
<diskStore path="java.io.tmpdir"/>
<defaultCache
maxElementsInMemory="10000"
eternal="false"
timeToIdleSeconds="120"
timeToLiveSeconds="120"
overflowToDisk="true"
diskPersistent="true"
diskExpiryThreadIntervalSeconds="120"
memoryStoreEvictionPolicy="LRU"
/>
<cache name="com.amazon.otb.model.DataElement"
maxElementsInMemory="600"
eternal="true"
overflowToDisk="false"
/>
</ehcache>