大量數據流動是web應用性能問題常見的原因，而緩存被廣泛的用於優化數據庫應用。cache 被設計爲通過保存從數據庫裏load的數據來減少應用和數據庫之間的數據流動。數據庫訪問只有當檢索的數據不在cache 裏可用時才必要。hibernate可以用兩種不同的對象緩存：first-level cache 和 second-level cache 。first-level cache 和Session對象關聯，而second-level cache 是和Session Factory對象關聯。
缺省地，hibernate已經使用基於每個事務的first-level cache 。Hibernate用first-level cache 主要是減少在一個事務內的sql查詢數量。例如，如果一個對象在同一個事務內被修改多次，hibernate將只生成一個包括所有修改的UPDATE SQL語句。爲了減少數據流動，second-level cache 在Session Factory級的不同事務之間保持load的對象，這些對象對整個應用可用，不只是對當前用戶正在運行的查詢。這樣，每次查詢將返回已經load在緩存裏的對象，避免一個或更多潛在的數據庫事務。
下載ehcache ，hibernate3 .2必須要ehcache1.2以上才能支持。可以修改log4j配置文件log4j.logger.net.sf.hibernate.cache =debug查看日誌
1.在類路徑上ehcache.xml：
<ehcache>
<!-- Sets the path to the directory where cache .data files are created.
If the path is a Java System Property it is replaced by
its value in the running VM.The following properties are translated:
user.home - User's home directory
user.dir - User's current working directory
java.io.tmpdir - Default temp file path -->
<diskStore path="java.io.tmpdir"/>
<!--Default Cache configuration. These will applied to caches programmatically created through
the CacheManager.The following attributes are required:
maxElementsInMemory - Sets the maximum number of objects that will be created in memory
eternal - Sets whether elements are eternal. If eternal, timeouts are ignored and the
element is never expired.
overflowToDisk - Sets whether elements can overflow to disk when the in-memory cache
has reached the maxInMemory limit.The following attributes are optional:
timeToIdleSeconds - Sets the time to idle for an element before it expires.
i.e. The maximum amount of time between accesses before an element expires
Is only used if the element is not eternal.
Optional attribute. A value of 0 means that an Element can idle for infinity.
The default value is 0.
timeToLiveSeconds - Sets the time to live for an element before it expires.
i.e. The maximum time between creation time and when an element expires.
Is only used if the element is not eternal.
Optional attribute. A value of 0 means that and Element can live for infinity.
The default value is 0.
diskPersistent - Whether the disk store persists between restarts of the Virtual Machine.
The default value is false.
diskExpiryThreadIntervalSeconds- The number of seconds between runs of the disk expiry thread. The default value
is 120 seconds.
--><defaultCache
maxElementsInMemory="10000"
eternal="false"
overflowToDisk="true"
timeToIdleSeconds="120"
timeToLiveSeconds="120"
diskPersistent="false"
diskExpiryThreadIntervalSeconds="120"/>
<!-- See http://ehcache.sourceforge.net/documentation/#mozTocId258426 for how to configure caching for your objects -->
</ehcache>
2.applicationContext-hibernate.xml裏Hibernate SessionFactory配置：
<!-- Hibernate SessionFactory -->
<bean id="sessionFactory" class="org.springframework.orm.hibernate3 .LocalSessionFactoryBean">
<property name="dataSource" ref="dataSource"/>
<property name="configLocation"><value>classpath:hibernate.cfg.xml</value></property>
<!-- The property below is commented out b/c it doesn't work when run via
Ant in Eclipse. It works fine for individual JUnit tests and in IDEA ??
<property name="mappingJarLocations">
<list><value>file:dist/appfuse-dao.jar</value></list>
</property>
-->
<property name="hibernateProperties">
<props>
<prop key="hibernate.dialect">@HIBERNATE-DIALECT@</prop>
<!--<prop key="hibernate.show_sql">true</prop>-->
<prop key="hibernate.max_fetch_depth">3</prop>
<prop key="hibernate.hibernate.use_outer_join">true</prop>
<prop key="hibernate.jdbc.batch_size">10</prop>
<prop key="hibernate.cache .use_query_cache">true</prop>
<prop key="hibernate.cache .use_second_level_cache">true</prop>
<prop key="hibernate.cache .provider_class">org.hibernate.cache .EhCacheProvider</prop>
<!--
<prop key="hibernate.use_sql_comments">false</prop>
-->
<!-- Create/update the database tables automatically when the JVM starts up
<prop key="hibernate.hbm2ddl.auto">update</prop> -->
<!-- Turn batching off for better error messages under PostgreSQL
<prop key="hibernate.jdbc.batch_size">0</prop> -->
</props>
</property>
<property name="entityInterceptor">
<ref local="auditLogInterceptor"/>
</property>
</bean>
說 明：如果不設置“查詢緩存”，那麼hibernate只會緩存使用load()方法獲得的單個持久化對象，如果想緩存使用findall()、 list()、Iterator()、createCriteria()、createQuery()等方法獲得的數據結果集的話，就需要設置 hibernate.cache .use_query_cache true 纔行
3.model類裏採用Xdoclet生成*.hbm.xml裏的cache xml標籤，即<cache usage="read-only"/>
/**
* @hibernate.class table="WF_WORKITEM_HIS"
* @hibernate.cache usage="read-write"
*
*/
4.對於"query cache "，需要在程序裏編碼：
getHibernateTemplate().setCacheQueries(true);
return getHibernateTemplate().find(hql);