Hibernate学习40 -- 缓存管理3 -- 查询缓存
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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);
}
}
}
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