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java中hibernate二級(jí)緩存詳解

更新時(shí)間：2017年05月06日 15:54:12 作者：SIHAIloveYAN

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Hibernate的二級(jí)緩存

一、緩存概述

緩存(Cache): 計(jì)算機(jī)領(lǐng)域非常通用的概念。它介于應(yīng)用程序和永久性數(shù)據(jù)存儲(chǔ)源(如硬盤上的文件或者數(shù)據(jù)庫(kù))之間，其作用是降低應(yīng)用程序直接讀寫永久性數(shù)據(jù)存儲(chǔ)源的頻率，從而提高應(yīng)用的運(yùn)行性能。緩存中的數(shù)據(jù)是數(shù)據(jù)存儲(chǔ)源中數(shù)據(jù)的拷貝。緩存的物理介質(zhì)通常是內(nèi)存

hibernate中提供了兩個(gè)級(jí)別的緩存

第一級(jí)別的緩存是 Session 級(jí)別的緩存，它是屬于事務(wù)范圍的緩存。這一級(jí)別的緩存由 hibernate 管理的，一般情況下無(wú)需進(jìn)行干預(yù)

第二級(jí)別的緩存是 SessionFactory 級(jí)別的緩存，它是屬于進(jìn)程范圍的緩存

Hibernate 的緩存可以分為兩類:

內(nèi)置緩存: Hibernate 自帶的, 不可卸載. 通常在 Hibernate 的初始化階段, Hibernate 會(huì)把映射元數(shù)據(jù)和預(yù)定義的 SQL 語(yǔ)句放到 SessionFactory 的緩存中, 映射元數(shù)據(jù)是映射文件中數(shù)據(jù)的復(fù)制, 而預(yù)定義 SQL 語(yǔ)句時(shí) Hibernate 根據(jù)映射元數(shù)據(jù)推到出來(lái)的. 該內(nèi)置緩存是只讀的.

外置緩存(二級(jí)緩存): 一個(gè)可配置的緩存插件. 在默認(rèn)情況下, SessionFactory 不會(huì)啟用這個(gè)緩存插件. 外置緩存中的數(shù)據(jù)是數(shù)據(jù)庫(kù)數(shù)據(jù)的復(fù)制, 外置緩存的物理介質(zhì)可以是內(nèi)存或硬盤

二、理解二級(jí)緩存的并發(fā)訪問(wèn)策略

三、配置進(jìn)程范圍內(nèi)的二級(jí)緩存(配置ehcache緩存)

1 拷貝ehcache-1.5.0.jar到當(dāng)前工程的lib目錄下

依賴 backport-util-concurrent 和 commons-logging

2 開啟二級(jí)緩存

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

3 要指定緩存的供應(yīng)商

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

4 指定使用二級(jí)緩存的類

方法一在使用類的*.hbm.xml配置

選擇需要使用二級(jí)緩存的持久化類, 設(shè)置它的二級(jí)緩存的并發(fā)訪問(wèn)策略, <class> 元素的 cache 子元素表明 Hibernate 會(huì)緩存對(duì)象的簡(jiǎn)單屬性, 但不會(huì)緩存集合屬性, 若希望緩存集合屬性中的元素, 必須在 <set> 元素中加入 <cache> 子元素

方法二在hibernate.cfg.xml文件中配置(建議)

  <!-- 指定使用二級(jí)緩存的類 放在maping下面 -->
  <!-- 配置類級(jí)別的二級(jí)緩存 -->
  <class-cache class="com.sihai.c3p0.Customer" usage="read-write"/>
  <class-cache class="com.sihai.c3p0.Order" usage="read-write"/>
 
  <!-- 配置集合級(jí)別的二級(jí)緩存 -->
  <collection-cache collection="com.sihai.c3p0.Customer.orders" 
         usage="read-write"/>

5 配置ehcache默認(rèn)的配置文件ehcache.xml(名字固定)（放在類路徑下）

<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../config/ehcache.xsd"> 
 
 <diskStore path="c:/ehcache"/> 
 <defaultCache 
   maxElementsInMemory="5" 
   eternal="false" 
   timeToIdleSeconds="120" 
   timeToLiveSeconds="120" 
   overflowToDisk="true" 
   maxElementsOnDisk="10000000" 
   diskPersistent="false" 
   diskExpiryThreadIntervalSeconds="120" 
   memoryStoreEvictionPolicy="LRU" 
   /> 
</ehcache>

四、測(cè)試

package com.sihai.hibernate3.test; 
 
import java.util.Iterator; 
import java.util.List; 
 
import org.hibernate.Query; 
import org.hibernate.Session; 
import org.hibernate.Transaction; 
import org.junit.Test; 
 
import com.sihai.hibernate3.demo1.Customer; 
import com.sihai.hibernate3.demo1.Order; 
import com.sihai.utils.HibernateUtils; 
 
public class HibernateTest6 { 
  
 @Test 
 // 查詢緩存的測(cè)試 
 public void demo9(){ 
  Session session = HibernateUtils.getCurrentSession(); 
  Transaction tx = session.beginTransaction(); 
   
  Query query = session.createQuery("select c.cname from Customer c"); 
  // 使用查詢緩存: 
  query.setCacheable(true); 
  query.list(); 
   
  tx.commit(); 
   
  session = HibernateUtils.getCurrentSession(); 
  tx = session.beginTransaction(); 
   
  query = session.createQuery("select c.cname from Customer c"); 
  query.setCacheable(true); 
  query.list(); 
   
  tx.commit(); 
 } 
  
 @SuppressWarnings("unused") 
 @Test 
 // 更新時(shí)間戳 
 public void demo8(){ 
  Session session = HibernateUtils.getCurrentSession(); 
  Transaction tx = session.beginTransaction(); 
   
  Customer customer = (Customer) session.get(Customer.class, 2); 
  session.createQuery("update Customer set cname = '奶茶' where cid = 2").executeUpdate(); 
   
  tx.commit(); 
   
  session = HibernateUtils.getCurrentSession(); 
  tx = session.beginTransaction(); 
   
  Customer customer2 = (Customer) session.get(Customer.class, 2); 
   
  tx.commit(); 
 } 
  
 @SuppressWarnings("all") 
 @Test 
 // 將內(nèi)存中的數(shù)據(jù)寫到硬盤 
 public void demo7(){ 
  Session session = HibernateUtils.getCurrentSession(); 
  Transaction tx = session.beginTransaction(); 
   
  List<Order> list = session.createQuery("from Order").list(); 
   
  tx.commit(); 
 } 
  
 @Test 
 // 一級(jí)緩存的更新會(huì)同步到二級(jí)緩存: 
 public void demo6(){ 
  Session session = HibernateUtils.getCurrentSession(); 
  Transaction tx = session.beginTransaction(); 
   
  Customer customer = (Customer) session.get(Customer.class, 1); 
  customer.setCname("芙蓉"); 
   
  tx.commit(); 
   
  session = HibernateUtils.getCurrentSession(); 
  tx = session.beginTransaction(); 
   
  Customer customer2 = (Customer) session.get(Customer.class, 1); 
   
  tx.commit(); 
 } 
  
 @SuppressWarnings("unchecked") 
 @Test 
 // iterate()方法可以查詢所有信息. 
 // iterate方法會(huì)發(fā)送N+1條SQL查詢.但是會(huì)使用二級(jí)緩存的數(shù)據(jù) 
 public void demo5(){ 
  Session session = HibernateUtils.getCurrentSession(); 
  Transaction tx = session.beginTransaction(); 
   
  // N+1條SQL去查詢. 
  Iterator<Customer> iterator = session.createQuery("from Customer").iterate(); 
  while(iterator.hasNext()){ 
   Customer customer = iterator.next(); 
   System.out.println(customer); 
  } 
   
  tx.commit(); 
   
  session = HibernateUtils.getCurrentSession(); 
  tx = session.beginTransaction(); 
   
  iterator = session.createQuery("from Customer").iterate(); 
  while(iterator.hasNext()){ 
   Customer customer = iterator.next(); 
   System.out.println(customer); 
  } 
   
  tx.commit(); 
 } 
  
 @SuppressWarnings("unchecked") 
 @Test 
 // 查詢所有.Query接口的list()方法. 
 // list()方法會(huì)向二級(jí)緩存中放數(shù)據(jù),但是不會(huì)使用二級(jí)緩存中的數(shù)據(jù). 
 public void demo4(){ 
  Session session = HibernateUtils.getCurrentSession(); 
  Transaction tx = session.beginTransaction(); 
   
  // 查詢所有客戶: 
  // list方法會(huì)向二級(jí)緩存中放入數(shù)據(jù)的. 
  List<Customer> list = session.createQuery("from Customer").list(); 
  for (Customer customer : list) { 
   System.out.println(customer.getCname()); 
  } 
  tx.commit(); 
   
  session = HibernateUtils.getCurrentSession(); 
  tx = session.beginTransaction(); 
   
  // Customer customer = (Customer) session.get(Customer.class, 1);// 沒(méi)有發(fā)生SQL ,從二級(jí)緩存獲取的數(shù)據(jù). 
  // list()方法沒(méi)有使用二級(jí)緩存的數(shù)據(jù). 
  list = session.createQuery("from Customer").list(); 
  for (Customer customer : list) { 
   System.out.println(customer.getCname()); 
  } 
   
  tx.commit(); 
 } 
  
 @Test 
 // 二級(jí)緩存的集合緩沖區(qū)特點(diǎn): 
 public void demo3(){ 
  Session session = HibernateUtils.getCurrentSession(); 
  Transaction tx = session.beginTransaction(); 
   
  Customer customer = (Customer) session.get(Customer.class, 1); 
  // 查詢客戶的訂單. 
  System.out.println("訂單的數(shù)量:"+customer.getOrders().size()); 
   
  tx.commit(); 
   
  session = HibernateUtils.getCurrentSession(); 
  tx = session.beginTransaction(); 
   
  Customer customer2 = (Customer) session.get(Customer.class, 1); 
  // 查詢客戶的訂單. 
  System.out.println("訂單的數(shù)量:"+customer2.getOrders().size()); 
   
  tx.commit(); 
 } 
  
 @SuppressWarnings("unused") 
 @Test 
 // 配置二級(jí)緩存的情況 
 public void demo2(){ 
  Session session = HibernateUtils.getCurrentSession(); 
  Transaction tx = session.beginTransaction(); 
   
  Customer customer1 = (Customer) session.get(Customer.class, 1);// 發(fā)送SQL. 
   
  Customer customer2 = (Customer) session.get(Customer.class, 1);// 不發(fā)送SQL. 
   
  System.out.println(customer1 == customer2); 
   
  tx.commit(); 
   
  session = HibernateUtils.getCurrentSession(); 
  tx = session.beginTransaction(); 
   
  Customer customer3 = (Customer) session.get(Customer.class, 1);// 不發(fā)送SQL. 
  Customer customer4 = (Customer) session.get(Customer.class, 1);// 不發(fā)送SQL. 
   
  System.out.println(customer3 == customer4); 
   
  tx.commit(); 
 } 
  
  
 @SuppressWarnings("unused") 
 @Test 
 // 沒(méi)有配置二級(jí)緩存的情況 
 public void demo1(){ 
  Session session = HibernateUtils.getCurrentSession(); 
  Transaction tx = session.beginTransaction(); 
   
  Customer customer1 = (Customer) session.get(Customer.class, 1);// 發(fā)送SQL. 
   
  Customer customer2 = (Customer) session.get(Customer.class, 1);// 不發(fā)送SQL. 
   
   
   
  tx.commit(); 
   
  session = HibernateUtils.getCurrentSession(); 
  tx = session.beginTransaction(); 
   
  Customer customer3 = (Customer) session.get(Customer.class, 1);// 發(fā)送SQL. 
   
   
  tx.commit(); 
 } 
}

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