hibernate二级缓存

Java代码
public class User implements Serializable{

public Long id;
private String name;
private int age;

}

public class User implements Serializable{

public Long id;
private String name;
private int age;

}
映射文件就省略啦，大家应该都会写的。

再来看看hibernate配置文件：

Xml代码
<property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property>
<property name="hibernate.cache.use_second_level_cache">true</property>
<property name="hibernate.cache.use_query_cache">true</property>

<property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property>
<property name="hibernate.cache.use_second_level_cache">true</property>
<property name="hibernate.cache.use_query_cache">true</property> 我们看到provider_class中我们指定了ehcache这个提供类，所以我们也需要ehcache.xml放在classpath中：

Xml代码
<?xml version="1.0" encoding="UTF-8"?>
<ehcache>
<diskStore path="java.io.path"/>
<defaultCache
maxElementsInMemory="10000"
eternal="false"
timeToIdleSeconds="120"
timeToLiveSeconds="120"
overflowToDisk="true"
/>
</ehcache>

<?xml version="1.0" encoding="UTF-8"?>
<ehcache>
<diskStore path="java.io.path"/>
<defaultCache
maxElementsInMemory="10000"
eternal="false"
timeToIdleSeconds="120"
timeToLiveSeconds="120"
overflowToDisk="true"
/>
</ehcache> 接下来，我们直接看一下测试方法：

Java代码
public static void main(String[] args) {

Configuration cfg = new Configuration().configure();
SessionFactory sessionFactory = cfg.buildSessionFactory();
Session session = sessionFactory.openSession();

Query query = session.createQuery("from User user where name = 'shun123'");
Iterator iter = query.iterate();
while(iter.hasNext()) {
System.out.println(((User)iter.next()).getName());
}

session.close();

Session session2 = sessionFactory.openSession();
Query query2 = session2.createQuery("from User user where name='shun123'");
Iterator iter2 = query2.iterate();
while(iter2.hasNext()) {
System.out.println(((User)iter2.next()).getName());
}

session2.close();

}

public static void main(String[] args) {

Configuration cfg = new Configuration().configure();
SessionFactory sessionFactory = cfg.buildSessionFactory();
Session session = sessionFactory.openSession();

Query query = session.createQuery("from User user where name = 'shun123'");
Iterator iter = query.iterate();
while(iter.hasNext()) {
System.out.println(((User)iter.next()).getName());
}

session.close();

Session session2 = sessionFactory.openSession();
Query query2 = session2.createQuery("from User user where name='shun123'");
Iterator iter2 = query2.iterate();
while(iter2.hasNext()) {
System.out.println(((User)iter2.next()).getName());
}

session2.close();

} 运行后可以看到：

Java代码
Hibernate: select user0_.USER_ID as col_0_0_ from USER user0_ where user0_.USER_NAME='shun123'
Hibernate: select user0_.USER_ID as USER1_0_0_, user0_.USER_NAME as USER2_0_0_, user0_.age as age0_0_ from USER user0_ where user0_.USER_ID=?
shun123
Hibernate: select user0_.USER_ID as col_0_0_ from USER user0_ where user0_.USER_NAME='shun123'
shun123

Hibernate: select user0_.USER_ID as col_0_0_ from USER user0_ where user0_.USER_NAME='shun123'
Hibernate: select user0_.USER_ID as USER1_0_0_, user0_.USER_NAME as USER2_0_0_, user0_.age as age0_0_ from USER user0_ where user0_.USER_ID=?
shun123
Hibernate: select user0_.USER_ID as col_0_0_ from USER user0_ where user0_.USER_NAME='shun123'
shun123 我们可以看到它只执行了一句搜索，而在第二次查询时并没有取出ID进行搜索，这主要归功于二级缓存。



下面我们先分析一下测试方法中的代码。测试方法中我们分别打开了两个Session并且分别创建两个Query进行相同的查询。但两次Session可以共用缓存，这也就是二级缓存，SessionFactory级的缓存。只要我们的Session由同一个SessionFactory创建，那么我们就可以共用二级缓存减少与数据库的交互。

我们再来看一下配置文件中的意思：

Xml代码
<property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property>
<property name="hibernate.cache.use_second_level_cache">true</property>
<property name="hibernate.cache.use_query_cache">true</property>

<property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property>
<property name="hibernate.cache.use_second_level_cache">true</property>
<property name="hibernate.cache.use_query_cache">true</property> 如果我们需要使用二级缓存，首先需要配置：

Xml代码
<property name="hibernate.cache.use_second_level_cache">true</property>

<property name="hibernate.cache.use_second_level_cache">true</property> 进行开户二级缓存，然后通过：

Xml代码
<property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property>

<property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property> 指定二级缓存的提供类，一般情况下我们都用ehcache，其他我的暂时没用到，也不太清楚，所以暂时不讲了。

像我们刚才的例子，我们只需要配置上面两个，完全可以正常运行，利用二级缓存。

那么第三句是干什么用的呢？

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

<property name="hibernate.cache.use_query_cache">true</property> 这个配置指明了我们在查询时需要利用缓存，如果我们需要用到这个要事先调用query.setCacheable(true)这个方法来进行启用。



我们一起来看代码（我们先不启用缓存）：

Java代码
public static void main(String[] args) {

Configuration cfg = new Configuration().configure();
SessionFactory sessionFactory = cfg.buildSessionFactory();
Session session = sessionFactory.openSession();

Query query = session.createQuery("from User user where name = 'shun123'");
List list = query.list();
for (int i = 0; i < list.size(); i++){
System.out.println(((User)list.get(i)).getName());
}

session.close();

Session session2 = sessionFactory.openSession();
Query query2 = session2.createQuery("from User user where name='shun123'");
List list2 = query2.list();
for (int i = 0; i < list2.size(); i++){
System.out.println(((User)list.get(i)).getName());
}

session2.close();

}

public static void main(String[] args) {

Configuration cfg = new Configuration().configure();
SessionFactory sessionFactory = cfg.buildSessionFactory();
Session session = sessionFactory.openSession();

Query query = session.createQuery("from User user where name = 'shun123'");
List list = query.list();
for (int i = 0; i < list.size(); i++){
System.out.println(((User)list.get(i)).getName());
}

session.close();

Session session2 = sessionFactory.openSession();
Query query2 = session2.createQuery("from User user where name='shun123'");
List list2 = query2.list();
for (int i = 0; i < list2.size(); i++){
System.out.println(((User)list.get(i)).getName());
}

session2.close();

} 这里输出的结果是：

Java代码
Hibernate: select user0_.USER_ID as USER1_0_, user0_.USER_NAME as USER2_0_, user0_.age as age0_ from USER user0_ where user0_.USER_NAME='shun123'
shun123
Hibernate: select user0_.USER_ID as USER1_0_, user0_.USER_NAME as USER2_0_, user0_.age as age0_ from USER user0_ where user0_.USER_NAME='shun123'
shun123

Hibernate: select user0_.USER_ID as USER1_0_, user0_.USER_NAME as USER2_0_, user0_.age as age0_ from USER user0_ where user0_.USER_NAME='shun123'
shun123
Hibernate: select user0_.USER_ID as USER1_0_, user0_.USER_NAME as USER2_0_, user0_.age as age0_ from USER user0_ where user0_.USER_NAME='shun123'
shun123
我们看到，它并没有利用缓存，因为我们这里用了list，而list对缓存是只写不读的。所以这里会进行两次查询。

那么我们来修改一下：

Java代码
public static void main(String[] args) {

Configuration cfg = new Configuration().configure();
SessionFactory sessionFactory = cfg.buildSessionFactory();
Session session = sessionFactory.openSession();

Query query = session.createQuery("from User user where name = 'shun123'");
<SPAN style="BACKGROUND-COLOR: #ffffff"><SPAN style="COLOR: #ff0000">query.setCacheable(true);</SPAN></SPAN>
List list = query.list();
for (int i = 0; i < list.size(); i++){
System.out.println(((User)list.get(i)).getName());
}

session.close();

Session session2 = sessionFactory.openSession();
Query query2 = session2.createQuery("from User user where name='shun123'");
<SPAN style="COLOR: #ff0000">query2.setCacheable(true);</SPAN>
List list2 = query2.list();
for (int i = 0; i < list2.size(); i++){
System.out.println(((User)list.get(i)).getName());
}

session2.close();

}

public static void main(String[] args) {

Configuration cfg = new Configuration().configure();
SessionFactory sessionFactory = cfg.buildSessionFactory();
Session session = sessionFactory.openSession();

Query query = session.createQuery("from User user where name = 'shun123'");
query.setCacheable(true);
List list = query.list();
for (int i = 0; i < list.size(); i++){
System.out.println(((User)list.get(i)).getName());
}

session.close();

Session session2 = sessionFactory.openSession();
Query query2 = session2.createQuery("from User user where name='shun123'");
query2.setCacheable(true);
List list2 = query2.list();
for (int i = 0; i < list2.size(); i++){
System.out.println(((User)list.get(i)).getName());
}

session2.close();

} 看到红色的两句代码，这是我们进行添加的两个开启查询缓存的代码，现在我们看到结果：

Java代码
Hibernate: select user0_.USER_ID as USER1_0_, user0_.USER_NAME as USER2_0_, user0_.age as age0_ from USER user0_ where user0_.USER_NAME='shun123'
shun123
shun123

Hibernate: select user0_.USER_ID as USER1_0_, user0_.USER_NAME as USER2_0_, user0_.age as age0_ from USER user0_ where user0_.USER_NAME='shun123'
shun123
shun123 只剩一次查询了，为什么呢？就在那两句红色代码处，我们开启了缓存，记住，需要使用两次。把两个query都设成可缓存的才能使用查询缓存。

Criteria也是类似的做法，为免有些童鞋忘记了Criteria怎么写了，我还是放一下代码：

Java代码
public static void main(String[] args) {

Configuration cfg = new Configuration().configure();
SessionFactory sessionFactory = cfg.buildSessionFactory();
Session session = sessionFactory.openSession();

Criteria criteria1 = session.createCriteria(User.class);
criteria1.setCacheable(true);
criteria1.add(Restrictions.eq("name","shun123"));
List list = criteria1.list();
for (int i = 0; i < list.size(); i++){
System.out.println(((User)list.get(i)).getName());
}

session.close();

Session session2 = sessionFactory.openSession();
Criteria criteria2 = session2.createCriteria(User.class);
criteria2.setCacheable(true);
criteria2.add(Restrictions.eq("name","shun123"));
List list2 = criteria2.list();
for (int i = 0; i < list2.size(); i++){
System.out.println(((User)list.get(i)).getName());
}

session2.close();

}

public static void main(String[] args) {

Configuration cfg = new Configuration().configure();
SessionFactory sessionFactory = cfg.buildSessionFactory();
Session session = sessionFactory.openSession();

Criteria criteria1 = session.createCriteria(User.class);
criteria1.setCacheable(true);
criteria1.add(Restrictions.eq("name","shun123"));
List list = criteria1.list();
for (int i = 0; i < list.size(); i++){
System.out.println(((User)list.get(i)).getName());
}

session.close();

Session session2 = sessionFactory.openSession();
Criteria criteria2 = session2.createCriteria(User.class);
criteria2.setCacheable(true);
criteria2.add(Restrictions.eq("name","shun123"));
List list2 = criteria2.list();
for (int i = 0; i < list2.size(); i++){
System.out.println(((User)list.get(i)).getName());
}

session2.close();

} 我们看结果：

Java代码
Hibernate: select this_.USER_ID as USER1_0_0_, this_.USER_NAME as USER2_0_0_, this_.age as age0_0_ from USER this_ where this_.USER_NAME=?
shun123
shun123