hibernate3学习笔记(二) 一级缓存[Java编程]

接上例:http://www.bianceng.cn/Programming/Java/201101/23637.htm

改正BusinessService．ｊａｖａ文件以下所示:

1.package com.hb3.pack_01;
2.
3.import org.hibernate.Session;
4.import org.hibernate.SessionFactory;
5.import org.hibernate.cfg.Configuration;
6.
7.import com.hb3.pack_01.model.User;
8.
9.public class BusinessService {
10.
11.    public static void main(String[] args) {
12.
13.        Configuration config = new Configuration().configure();
14.        SessionFactory sessionFactory = config.buildSessionFactory();
15.        Session session = sessionFactory.openSession();
16.
17.        User user1 = (User) session.load(User.class, new Integer(1));
18.        User user2 = (User) session.load(User.class, new Integer(1));
19.        System.out.println(user1 == user2);
20.
21.        user1 = (User) session.load(User.class, new Integer(1));
22.        session.evict(user1);
23.        user2 = (User) session.load(User.class, new Integer(1));
24.        System.out.println(user1 == user2);
25.
26.        user1 = (User) session.load(User.class, new Integer(1));
27.        session.clear();
28.        user2 = (User) session.load(User.class, new Integer(1));
29.        System.out.println(user1 == user2);
30.
31.        Session session1 = sessionFactory.openSession();
32.        user1 = (User) session1.load(User.class, new Integer(1));
33.        session1.close();
34.        Session session2 = sessionFactory.openSession();
35.        user2 = (User)session2.load(User.class, new Integer(1));
36.        session2.close();
37.        System.out.println(user1 == user2);
38.
39.        session.close();
40.        sessionFactory.close();
41.    }
42.}

顺次打印出的后果为

true

false

false

false

可见:

利用session.evict大概session.clear把某个物体从缓存中移除,大概直接关闭Session,城市使缓存失效,大概说释放缓存占用的资源空间.

值得一提的是:在载入大量数据时,应当及时手动排除一级缓存以释放资源.

比方:

1.Session session = sessionFactory.openSession();
2.Transaction tx = session.beginTransaction();
3.
4.while(....) { // 大量載入物件時的迴圈表示
5.    ....
6.    session.save(someObject);
7.    if(count % 100 == 0) { // 每100筆資料
8.        session.flush(); // 送入資料庫
9.        session.clear(); // 排除快取
10.    }
11.}
12.
13.tx.commit();
14.session.close();

在SQL Server、Oracle等数据库可以利用ｈｉｂｅｒｎａｔｅ的配置文件举行配置,如:

1.....
2.<hibernate-configuration>
3.    <session-factory>
4.        ....
5.        <property name="hibernate.jdbc.batch_size">100</property>
6.        ....
7.    </session-factory>
8.<hibernate-configuration>

注意:在MySQL中不支持这种配置方法.