Hibernate学习40 -- 缓存管理3 -- 查询缓存

查询缓存是针对普通属性结果集的缓存，对实体对象的结果集只缓存id。查询缓存的生命周期，当前关联的表发生修改，那么查询缓存生命周期结束。

查询缓存的配置和使用：

²        在hibernate.cfg.xml文件中启用查询缓存，添加以下代码：

<property name="hibernate.cache.use_query_cache">true</property>

²        在程序中必须手动启用查询缓存，如：query.setCacheable(true);

 

例子代码如下：

hibernate.cfg.xml： <hibernate-configuration>     <session-factory>        <property name="hibernate.connection.url">            jdbc:mysql://localhost/hibernate_cache        </property>        <property name="hibernate.connection.driver_class">            com.mysql.jdbc.Driver        </property>        <property name="hibernate.connection.username">            root        </property>        <property name="hibernate.connection.password">            root        </property>        <property name="hibernate.dialect">            org.hibernate.dialect.MySQLDialect        </property>        <property name="hibernate.show_sql">true</property>          <!-- 开启二级缓存 -->        <property name="hibernate.cache.use_second_level_cache">            true        </property>          <!-- 指定缓存产品提供商 -->        <property name="hibernate.cache.provider_class">            org.hibernate.cache.EhCacheProvider        </property>          <!-- 启用查询缓存 -->        <property name="hibernate.cache.use_query_cache">            true        </property>          <mapping resource="hibernate/Classes.hbm.xml" />        <mapping resource="hibernate/Student.hbm.xml" />          <class-cache class="hibernate.Student"            usage="read-only" />     </session-factory> </hibernate-configuration> 测试代码： public class CacheLevel2Test extends TestCase {     /**      * 开启查询缓存，关闭二级缓存      * 开启一个session，分别调用query.list      */     public void testCache1() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();                       Query query = session.createQuery ("select s.name from Student s");            //启用查询查询缓存            query.setCacheable(true);                       List names = query.list();            for (Iterator iter=names.iterator();iter.hasNext(); ) {               String name = (String)iter.next();               System.out.println(name);            }                       System.out.println("----------------------------");            query = session.createQuery ("select s.name from Student s");            //启用查询查询缓存            query.setCacheable(true);                       //没有发出查询sql，因为启用了查询缓存            names = query.list();            for (Iterator iter=names.iterator();iter.hasNext(); ) {               String name = (String)iter.next();               System.out.println(name);            }              session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }     }           /**      * 开启查询缓存，关闭二级缓存      * 开启两个session，分别调用query.list      */     public void testCache2() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();                       Query query = session.createQuery ("select s.name from Student s");            //启用查询查询缓存            query.setCacheable(true);                       List names = query.list();            for (Iterator iter=names.iterator();iter.hasNext(); ) {               String name = (String)iter.next();               System.out.println(name);            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }               System.out.println("--------------------------------");               try {            session = HibernateUtils.getSession();            session.beginTransaction();                       Query query = session.createQuery ("select s.name from Student s");            //启用查询查询缓存            query.setCacheable(true);                       //不会发出查询sql，因为查询缓存的生命周期和session无关            List names = query.list();            for (Iterator iter=names.iterator();iter.hasNext(); ) {               String name = (String)iter.next();               System.out.println(name);            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }     }              /**      * 开启查询缓存，关闭二级缓存      *      * 开启两个session，分别调用query.iterate      */     public void testCache3() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();                       Query query = session.createQuery ("select s.name from Student s");            //启用查询查询缓存            query.setCacheable(true);                         for (Iterator iter=query.iterate();iter.hasNext(); ) {               String name = (String)iter.next();               System.out.println(name);            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }               System.out.println("-------------------------------");               try {            session = HibernateUtils.getSession();            session.beginTransaction();                       Query query = session.createQuery ("select s.name from Student s");            //启用查询查询缓存            query.setCacheable(true);                         //查询缓存只对query.list()起作用，query.iterate不起作用， 也就是query.iterate不使用            //查询缓存            for (Iterator iter=query.iterate();iter.hasNext(); ) {               String name = (String)iter.next();               System.out.println(name);            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }     }         /**      * 关闭查询缓存，关闭二级缓存      * 开启两个session，分别调用query.list查询实体对象      */     public void testCache4() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();                       Query query = session.createQuery ("select s from Student s");            //启用查询查询缓存            //query.setCacheable(true);                       List students = query.list();            for (Iterator iter=students.iterator(); iter.hasNext(); ) {               Student student = (Student)iter.next();               System.out.println(student.getName());            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }               System.out.println("-------------------------------");               try {            session = HibernateUtils.getSession();            session.beginTransaction();                       Query query = session.createQuery ("select s from Student s");            //启用查询查询缓存            //query.setCacheable(true);            //会发出查询sql，因为list默认每次都会发出查询sql            List students = query.list();            for (Iterator iter=students.iterator(); iter.hasNext(); ) {               Student student = (Student)iter.next();               System.out.println(student.getName());            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }     }            /**      * 开启查询缓存，关闭二级缓存      *      * 开启两个session，分别调用query.list查询实体对象      */     public void testCache5() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();                       Query query = session.createQuery ("select s from Student s");            //启用查询查询缓存            query.setCacheable(true);                       List students = query.list();            for (Iterator iter=students.iterator(); iter.hasNext(); ) {               Student student = (Student)iter.next();               System.out.println(student.getName());            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }               System.out.println("--------------------------------");               try {            session = HibernateUtils.getSession();            session.beginTransaction();                       Query query = session.createQuery ("select s from Student s");            //启用查询查询缓存            query.setCacheable(true);                       //会发出n条查询语句，因为开启了查询缓存，关闭了二级缓存， 那么查询缓存会缓存实体对象的id            //所以hibernate会根据实体对象的id去查询相应的实体， 如果缓存中不存在相应的            //实体那么将发出根据实体id查询的sql语句， 否则不会发出sql使用缓存中的数据            List students = query.list();            for (Iterator iter=students.iterator(); iter.hasNext(); ) {               Student student = (Student)iter.next();               System.out.println(student.getName());            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }     }           /**      * 开启查询缓存，开启二级缓存      *      * 开启两个session，分别调用query.list查询实体对象      */     public void testCache6() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();                       Query query = session.createQuery ("select s from Student s");            //启用查询查询缓存            query.setCacheable(true);                       List students = query.list();            for (Iterator iter=students.iterator(); iter.hasNext(); ) {               Student student = (Student)iter.next();                System.out.println(student.getName());            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }               System.out.println("------------------------------");               try {            session = HibernateUtils.getSession();            session.beginTransaction();                       Query query = session.createQuery ("select s from Student s");            //启用查询查询缓存            query.setCacheable(true);                       //不会发出查询sql，因为开启了二级缓存和查询缓存， 查询缓存缓存了实体对象的id列表            //hibernate会根据实体对象的id列表到二级缓存中取得相应的数据            List students = query.list();            for (Iterator iter=students.iterator(); iter.hasNext(); ) {               Student student = (Student)iter.next();               System.out.println(student.getName());            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }     }      }