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标题: 【上海校区】Hibernate中一级缓存、二级缓存及查询缓存的... [打印本页]

作者: 小影姐姐 时间: 2018-5-11 12:02
标题: 【上海校区】Hibernate中一级缓存、二级缓存及查询缓存的...
1.一级缓存

1.1什么是一级缓存
一级缓存指的是Session级别的缓存，通过session查询id为1的对象，session不关闭，再次查询id为1的对象，不会发送sql语句。

1.2验证一级缓存的存在
@Test
public void test1() {
         Session session = HibernateUtils.openSession();
         Transaction tx = session.beginTransaction();
         // 先查询id为1的客户，把查询出来的对象存放到session缓存里
         Customer customer1 = session.get(Customer.class, 1L);
         // 再次查询id为1的客户，session缓存里有，就不再发送sql语句查询数据库
         Customer customer2 = session.get(Customer.class, 1L);
         //两个对象是一致的
         System.out.println(customer1==customer2);
         tx.commit();
         // session一旦关闭，一级缓存就失效了
         session.close();
}

测试结果如下：
@Test
public void test2() {
         Session session = HibernateUtils.openSession();
         Transaction tx = session.beginTransaction();
         // 先查询id为1的客户，把查询出来的对象存放到session缓存里
         Customer customer1 = session.get(Customer.class, 1L);
         // session一旦关闭，一级缓存就失效了
         session.close();
         // 再次获取新的session
         session = HibernateUtils.openSession();
         tx = session.beginTransaction();
         // 再次查询id为1的客户，一级缓存中没有，就发送sql语句查询数据库
         Customer customer2 = session.get(Customer.class, 1L);
         //两个对象不一致
         System.out.println(customer1==customer2);
         tx.commit();
         session.close();
}

测试结果如下：

2.二级缓存
2.1什么是二级缓存
二级缓存是SessionFactory级别的缓存，可以跨Session存在。

2.2开启二级缓存
导入二级缓存所需要的jar包

在hibernate.cfg.xml中配置二级缓存的提供商

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
         <session-factory>
                  <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
                  <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate_itheima26</property>
                  <property name="hibernate.connection.username">root</property>
                  <property name="hibernate.connection.password">123456</property>
                  <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
                  <property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
                  <property name="hibernate.c3p0.max_size">20</property>
                  <property name="hibernate.c3p0.min_size">5</property>
                  <property name="hibernate.c3p0.timeout">5000</property>
                  <property name="hibernate.c3p0.idle_test_period">3000</property>
                  <property name="hibernate.show_sql">true</property>
                  <property name="hibernate.format_sql">false</property>
                  <property name="hibernate.hbm2ddl.auto">update</property>
                  <property name="hibernate.current_session_context_class">thread</property>
                  
                  <property name="hibernate.cache.region.factory_class">org.hibernate.cache.ehcache.EhCacheRegionFactory</property>
                  <mapping resource="cn/itcast/domain/Customer.hbm.xml"/>
         </session-factory>
</hibernate-configuration>

在映射文件中配置缓存策略

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>

      <class name="cn.itcast.domain.Customer" table="cst_customer">
            
            <cache usage="read-only"/>
            <id name="custId" column="cust_id">
                     <generator class="native"></generator>
            </id>
            <property name="custName" column="cust_name"></property>
            <property name="custSource" column="cust_source"></property>
            <property name="custIndustry" column="cust_industry"></property>
            <property name="custLevel" column="cust_level"></property>
            <property name="custAddress" column="cust_address"></property>
            <property name="custPhone" column="cust_phone"></property>
      </class>

</hibernate-mapping>

2.3验证二级缓存的存在

@Test
public void test3() {
         Session session = HibernateUtils.openSession();
         Transaction tx = session.beginTransaction();
         // 先查询id为1的客户，把查询出来的对象存放到session缓存里
         Customer customer1 = session.get(Customer.class, 1L);
         // session一旦关闭，一级缓存就失效了
         session.close();
         // 再次获取新的session
         session = HibernateUtils.openSession();
         tx = session.beginTransaction();
         // 再次查询id为1的客户，一级缓存中没有，就找二级缓存，二级缓存中存在，不用发送sql语句
         Customer customer2 = session.get(Customer.class, 1L);
         tx.commit();
         session.close();
}

测试结果如下：

3.查询缓存
3.1什么是查询缓存
所谓查询缓存，是指把hql语句查询得到的结果集缓存起来。

3.2配置查询缓存

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
         <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
         <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate_itheima26</property>
         <property name="hibernate.connection.username">root</property>
         <property name="hibernate.connection.password">123456</property>
         <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
         <property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
         <property name="hibernate.c3p0.max_size">20</property>
         <property name="hibernate.c3p0.min_size">5</property>
         <property name="hibernate.c3p0.timeout">5000</property>
         <property name="hibernate.c3p0.idle_test_period">3000</property>
         <property name="hibernate.show_sql">true</property>
         <property name="hibernate.format_sql">false</property>
         <property name="hibernate.hbm2ddl.auto">update</property>
         <property name="hibernate.current_session_context_class">thread</property>
         
         <property name="hibernate.cache.region.factory_class">org.hibernate.cache.ehcache.EhCacheRegionFactory</property>
         
         <property name="hibernate.cache.use_query_cache">true</property>
         <mapping resource="cn/itcast/domain/Customer.hbm.xml"/>
         </session-factory>
</hibernate-configuration>

3.3验证查询缓存的存在

@Test
public void test4() {
         Session session = HibernateUtils.openSession();
         Transaction tx = session.beginTransaction();

         Query query1 = session.createQuery("select custId,custName from Customer");
         //把查询的结果放到查询缓存中
         query1.setCacheable(true);
         //iterator方法不会使用缓存
         query1.list();
         tx.commit();
         session.close();

         session = HibernateUtils.openSession();
         tx = session.beginTransaction();
         // 只发出一条查询语句，第二次查询不发出语句
         Query query2 = session.createQuery("select custId,custName from Customer");
         // 从查询缓存中取数据
         query2.setCacheable(true);
         query2.list();
         tx.commit();
         session.close();
}

测试结果如下：

1.png (17.62 KB, 下载次数: 11)

2.png (20.83 KB, 下载次数: 15)

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