hibernate 2级缓存

二级缓存也称进程级的缓存或SessionFactory级的缓存，二级缓存可以被所有的session共享
二级缓存的生命周期和SessionFactory的生命周期一致，SessionFactory可以管理二级缓存

二级缓存的配置和使用：
    * 将echcache.xml文件拷贝到src下
    * 开启二级缓存，修改hibernate.cfg.xml文件
        <property name="hibernate.cache.use_second_level_cache">true</property>
    * 指定缓存产品提供商，修改hibernate.cfg.xml文件
        <property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property>
    * 指定那些实体类使用二级缓存（两种方法）
        * 在映射文件中采用<cache>标签
<!--
       <cache usage="read-only"/>
   
   -->
        * 在hibernate.cfg.xml文件中，采用<class-cache>标签
               <class-cache class="com.bjsxt.hibernate.Student" usage="read-only"/>

二级缓存是缓存实体对象的

了解一级缓存和二级缓存的交互       
       
                
                    package com.bjsxt.hibernate;

import java.io.Serializable;

import org.hibernate.CacheMode;
import org.hibernate.Session;
import org.hibernate.SessionFactory;

import junit.framework.TestCase;

public class CacheLevel2Test extends TestCase {

    /**
     * 开启两个session，分别调用load
     */
    public void testCache1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
           
            Student student = (Student)session.load(Student.class, 1);
            System.out.println("student.name=" + student.getName());
           
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
       
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
           
            //不会发出sql，因为开启了二级缓存，session是共享二级缓存的
            Student student = (Student)session.load(Student.class, 1);
            System.out.println("student.name=" + student.getName());
           
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
       
    }  
   
    /**
     * 开启两个session，分别调用get
     */
    public void testCache2() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
           
            Student student = (Student)session.get(Student.class, 1);
            System.out.println("student.name=" + student.getName());
           
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
       
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
           
            //不会发出sql，因为开启了二级缓存，session是共享二级缓存的
            Student student = (Student)session.get(Student.class, 1);
            System.out.println("student.name=" + student.getName());
           
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }  
   
    /**
     * 开启两个session，分别调用load,在使用SessionFactory清除二级缓存
     */
    public void testCache3() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
           
            Student student = (Student)session.load(Student.class, 1);
            System.out.println("student.name=" + student.getName());
           
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
       
        //管理二级缓存
        SessionFactory factory = HibernateUtils.getSessionFactory();
        //factory.evict(Student.class);
        factory.evict(Student.class, 1);
       
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
           
            //会发出查询sql，因为二级缓存中的数据被清除了
            Student student = (Student)session.load(Student.class, 1);
            System.out.println("student.name=" + student.getName());
           
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }
   
   
    /**
     * 一级缓存和二级缓存的交互
     */
    public void testCache4() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
           
            //仅向二级缓存读数据，而不向二级缓存写数据
            session.setCacheMode(CacheMode.GET);
            Student student = (Student)session.load(Student.class, 1);
            System.out.println("student.name=" + student.getName());
           
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
       
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
           
            //发出sql语句，因为session设置了CacheMode为GET，所以二级缓存中没有数据
            Student student = (Student)session.load(Student.class, 1);
            System.out.println("student.name=" + student.getName());
           
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
       
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
           
            //只向二级缓存写数据，而不从二级缓存读数据
            session.setCacheMode(CacheMode.PUT);
           
            //会发出查询sql，因为session将CacheMode设置成了PUT
            Student student = (Student)session.load(Student.class, 1);
            System.out.println("student.name=" + student.getName());
           
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
       
    }  
}