EhCache使用详细介绍
?
??????? s = HibernateSessionFactory.getSession();
??????? c = s.createCriteria(Xyz.class);
??????? c.setCacheable(true);//这句必须要有
??????? System.out.println("第二次读取");
??????? l = c.list();
??????? System.out.println(l.size());
??????? HibernateSessionFactory.closeSession();
?? 4.5这时你会看到打印出来的信息为(表示第二次并没有去读库):
??????? 第一次读取
??????? Hibernate: *******
??????? 13
??????? 第二次读取
??????? 13
配置Spring+hibernate使用ehcache作为second-level cache
大量数据流动是web应用性能问题常见的原因,而缓存被广泛的用于优化数据库应用。cache被设计为通过保存从数据库里load的数据来减少应用和数据库之间的数据流动。数据库访问只有当检索的数据不在cache里可用时才必要。hibernate可以用两种不同的对象缓存:first-level cache 和 second-level cache。first-level cache和Session对象关联,而second-level cache是和Session Factory对象关联。
??????? 缺省地,hibernate已经使用基于每个事务的first-level cache。 Hibernate用first-level cache主要是减少在一个事务内的sql查询数量。例如,如果一个对象在同一个事务内被修改多次,hibernate将只生成一个包括所有修改的 UPDATE SQL语句。为了减少数据流动,second-level cache在Session Factory级的不同事务之间保持load的对象,这些对象对整个应用可用,不只是对当前用户正在运行的查询。这样,每次查询将返回已经load在缓存里的对象,避免一个或更多潜在的数据库事务。
下载ehcache,hibernate3.2必须要ehcache1.2以上才能支持。可以修改log4j配置文件log4j.logger.net.sf.hibernate.cache=debug查看日志
1.在类路径上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里Hibernate SessionFactory配置:
???? <!-- Hibernate SessionFactory -->
???? <bean id="sessionFactory" 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>
说明:如果不设置“查询缓存”,那么hibernate只会缓存使用load()方法获得的单个持久化对象,如果想缓存使用findall()、 list()、Iterator()、createCriteria()、createQuery()等方法获得的数据结果集的话,就需要设置 hibernate.cache.use_query_cache true 才行
3.model类里采用Xdoclet生成*.hbm.xml里的cache xml标签,即<cache usage="read-only"/>
/**
* @hibernate.class table="WF_WORKITEM_HIS"
* @hibernate.cache usage="read-write"
*?
*/
4.对于"query cache",需要在程序里编码:
???????? getHibernateTemplate().setCacheQueries(true);
???????? return getHibernateTemplate().find(hql);
使用spring和hibernate配置ehcache和query cache
1、applicationContext.xml
<prop key="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</prop>
<prop key="hibernate.cache.use_query_cache">true</prop>?
这两句加到hibernateProperties中
<bean id="hibernateTemplate" />
</property>
<property name="cacheQueries">
?? <value>true</value>
</property>
</bean>
添加此bean到applicationcontext.xml中。在各个DAO的bean中,更改如下
<property name="sessionFactory">
<ref bean="sessionFactory" />
</property>
改为
<property name="hibernateTemplate">
<ref bean="hibernateTemplate" />
</property>
2、ehcache.xml文件放在classes根目录即可
3、pojo与ehcache.xml的配置关系
以com.ce.ceblog.pojos.CeblogJournal为例子
在CeblogJournal.hbm.xml中配置:
<class name="CeblogJournal" table="CEBLOG_JOURNAL" lazy="false">
<cache usage="read-write" region="ehcache.xml中的name的属性值"/>
注意:这一句需要紧跟在class标签下面,其他位置无效。
Ehcache.xml文件主体如下
<defaultCache maxElementsInMemory="10000" eternal="false" timeToIdleSeconds="1" timeToLiveSeconds="1" overflowToDisk="true" />
<cache name="com.ce.ceblog.pojos.CeblogJournal" maxElementsInMemory="10000" eternal="false" timeToIdleSeconds="300" timeToLiveSeconds="600" overflowToDisk="true" />
hbm文件查找cache方法名的策略:如果不指定hbm文件中的region="ehcache.xml中的name的属性值",则使用name名为 com.ce.ceblog.pojos.CeblogJournal的cache,如果不存在与类名匹配的cache名称,则用 defaultCache。
如果CeblogJournal包含set集合,则需要另行指定其cache
例如CeblogJournal包含ceblogReplySet集合,则需要
添加如下配置到ehcache.xml中
<cache name="com.ce.ceblog.pojos.CeblogJournal.ceblogReplySet"
maxElementsInMemory="10000" eternal="false" timeToIdleSeconds="300"
timeToLiveSeconds="600" overflowToDisk="true" />
另,针对查询缓存的配置如下:
<cache name="org.hibernate.cache.UpdateTimestampsCache"
maxElementsInMemory="5000"
eternal="true"
overflowToDisk="true"/>
<cache name="org.hibernate.cache.StandardQueryCache"
maxElementsInMemory="10000"
eternal="false"
timeToLiveSeconds="120"
overflowToDisk="true"/>
4、选择缓存策略依据:
<cache usage="transactional|read-write|nonstrict-read-write|read-only" />
ehcache不支持transactional,其他三种可以支持。
read- only:无需修改, 那么就可以对其进行只读 缓存,注意,在此策略下,如果直接修改数据库,即使能够看到前台显示效果,但是将对象修改至cache中会报error,cache不会发生作用。另:删 除记录会报错,因为不能在read-only模式的对象从cache中删除。
read-write:需要更新数据,那么使用读/写缓存 比较合适,前提:数据库不可以为serializable transaction isolation level(序列化事务隔离级别)
nonstrict-read-write:只偶尔需要更新数据(也就是说,两个事务同时更新同一记录的情况很不常见),也不需要十分严格的事务隔离,那么比较适合使用非严格读/写缓存策略。
5、调试时候使用log4j的log4j.logger.org.hibernate.cache=debug,更方便看到ehcache的操作过程,主要用于调试过程,实际应用发布时候,请注释掉,以免影响性能。
6、 使用ehcache,打印sql语句是正常的,因为query cache设置为true将会创建两个缓存区域:一个用于保存查询结果集 (org.hibernate.cache.StandardQueryCache);另一个则用于保存最近查询的一系列表的时间戳(org.hibernate.cache.UpdateTimestampsCache)。请注意:在查询缓存中,它并不缓存结果集中所包含的实体的确切状态;它只缓存这些实体的标识符属性的值、以及各值类型的结果。需要将打印sql语句与最近的cache内容相比较,将不同之处修改到cache中,所以查询缓存通常会和二级缓存一起使用。