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); } } }