Hibernate查询返存
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：
* 在hibernate.cfg.xml文件中启用查询缓存，如：
<property name="hibernate.cache.use_query_cache">true</property>
* 在程序中必须手动启用查询缓存，如：
query.setCacheable(true);
下面举例说明一下查询缓存的使用：
/**
* 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);
}
}