Hibernate缓存机制

hibernate缓存机制是hibernate中很重要的一个内容，我们来看下hibernate的缓存机制。

hibernate缓存分为：一级缓存、二级缓存、查询缓存

1、一级缓存

      又称为session缓存，生命周期相同，周期较短。也称为事务级别的缓存。

通过项目案例来简单了解下，项目结构如下：

Book实体类

public class Book {private int id;private String name;private double price;private String author;private Date pubDate;public Book() {}public Book(String name, double price) {super();this.name = name;this.price = price;}@Overridepublic String toString() {return "Book [id=" + id + ", name=" + name + ", price=" + price+ ", author=" + author + ", pubDate=" + pubDate + "]";}//省略get/set}

Book.hbm.xml配置文件

<hibernate-mapping package="com.test.pojo">      <class name="Book" table="book">          <id name="id">              <generator class="identity" />          </id>          <property name="author" />          <property name="name" />          <property name="price" />          <property name="pubDate" />      </class>  </hibernate-mapping>

hibernate.cfg.xml配置文件

<hibernate-configuration><session-factory><property name="connection.driver_class">com.mysql.jdbc.Driver</property><property name="connection.url">jdbc:mysql:///hibernatetest</property><property name="connection.username">root</property><property name="connection.password">root</property><property name="dialect">org.hibernate.dialect.MySQLDialect</property><property name="show_sql">true</property><property name="hbm2ddl.auto">update</property><mapping resource="com/test/pojo/Book.hbm.xml" /></session-factory></hibernate-configuration>

HibernateUtil类

public class HibernateUtil {private static Configuration cfg=null;private static SessionFactory factory=null;private static Session session=null;static{cfg=new Configuration().configure();factory=cfg.buildSessionFactory(new StandardServiceRegistryBuilder()        .applySettings(cfg.getProperties()).build());}public static Session getSession(){if(factory!=null)return session=factory.openSession();factory=cfg.buildSessionFactory(new StandardServiceRegistryBuilder()        .applySettings(cfg.getProperties()).build());return session=factory.openSession();}public static void closeSession(){if(session!=null && session.isOpen())session.close();}}

HibernateTest测试类，根据实体类配置文件生成数据库表

@Testpublic void testCreateDB(){Configuration cfg=new Configuration().configure();SchemaExport se=new SchemaExport(cfg);se.create(true, true);}

向数据库表插入数据

@Testpublic void testSave(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();Book book=new Book();book.setName("读者");book.setPrice(21.5);book.setAuthor("读者出版传媒有限公司");book.setPubDate(new Date());Book book1=new Book();book1.setName("蓝血人");book1.setPrice(50);book1.setAuthor("卫斯理");book1.setPubDate(new Date());Book book2=new Book();book2.setName("傲慢与偏见");book2.setPrice(80);book2.setAuthor("简.奥斯丁");book2.setPubDate(new Date());Book book3=new Book();book3.setName("中国历史");book3.setPrice(21.5);book3.setAuthor("人民");book3.setPubDate(new Date());session.save(book);session.save(book1);session.save(book2);session.save(book3);tx.commit();HibernateUtil.closeSession();}

接下来就是各种查询的缓存问题

1）get方法

@Testpublic void testGet(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();Book book=(Book) session.get(Book.class, 1);//发出sql语句取数据System.out.println(book.getName());System.out.println("============");book=(Book) session.get(Book.class, 1);System.out.println(book.getName());tx.commit();HibernateUtil.closeSession();}

控制台打印sql语句如下

Hibernate: select book0_.id as id1_0_0_, book0_.author as author2_0_0_, book0_.name as name3_0_0_, 

book0_.price as price4_0_0_, book0_.pubDate as pubDate5_0_0_ from book book0_ where book0_.id=?读者============读者

上面示例可以看出

get使用了一级缓存，用get查询时，首先检查缓存中是否有该数据，如果有直接从缓存中取数据，如果没有再查询数据库，并且将数据放入缓存中。

2）load方法

@Testpublic void testLoad(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();Book book=(Book) session.load(Book.class, 1);//发出sql语句取数据System.out.println(book.getName());System.out.println("============");book=(Book) session.load(Book.class, 1);System.out.println(book.getName());tx.commit();HibernateUtil.closeSession();}

控制台打印信息如下

Hibernate: select book0_.id as id1_0_0_, book0_.author as author2_0_0_, book0_.name as name3_0_0_, book0_.price as price4_0_0_, book0_.pubDate as pubDate5_0_0_ from book book0_ where book0_.id=?读者============读者

总结：

load方法使用了一级缓存，用load查数据时，首先检查缓存中是否有该数据，

如果有，直接从缓存中获取数据；如果没有，再去数据库查数据，然后将数据放入缓存中。load还支持lazy

3)先get，后load

@Testpublic void testGetLoad(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();Book book=(Book) session.get(Book.class, 1);//发出sql语句取数据System.out.println(book.getName());System.out.println("============");book=(Book) session.load(Book.class, 1);System.out.println(book.getName());tx.commit();HibernateUtil.closeSession();}

控制台打印信息如下：

Hibernate: select book0_.id as id1_0_0_, book0_.author as author2_0_0_, book0_.name as name3_0_0_, book0_.price as price4_0_0_, book0_.pubDate as pubDate5_0_0_ from book book0_ where book0_.id=?读者============读者

总结：

先用get，再用load，load同样从一级缓存中查找数据，如果有数据，直接取不用到数据库查询。

4）list方法

@Testpublic void testList(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();List<Book> list=session.createQuery("from Book").list();System.out.println("条数："+list.size());System.out.println("=========");list=session.createQuery("from Book").list();System.out.println("条数："+list.size());tx.commit();HibernateUtil.closeSession();}

控制台打印信息如下：

Hibernate: select book0_.id as id1_0_, book0_.author as author2_0_, book0_.name as name3_0_, book0_.price as price4_0_, book0_.pubDate as pubDate5_0_ from book book0_条数：4=========Hibernate: select book0_.id as id1_0_, book0_.author as author2_0_, book0_.name as name3_0_, book0_.price as price4_0_, book0_.pubDate as pubDate5_0_ from book book0_条数：4

总结：

list查数据不去缓存中查数据，但是list查出来的‘实体对象’数据，会放入缓存中。

5）先list，再get

@Testpublic void testList(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();List<Book> list=session.createQuery("from Book").list();System.out.println("条数："+list.size());System.out.println("=========");Book book=(Book) session.get(Book.class, 2);System.out.println("书名:"+book.getName());tx.commit();HibernateUtil.closeSession();}

控制台打印信息如下：

Hibernate: select book0_.id as id1_0_, book0_.author as author2_0_, book0_.name as name3_0_, book0_.price as price4_0_, book0_.pubDate as pubDate5_0_ from book book0_条数：4=========书名:蓝血人

总结：

先用list查询，list查出来的实体对象数据，放入缓存中。然后用get直接从缓存中取数据。

6）先list，后uniqueResult

@Testpublic void testListUniqueResult(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();List<String> list=session.createQuery("select name from Book").list();System.out.println("条数："+list.size());System.out.println("=========");Object bookName=session.createQuery("select name from Book where id=:id").setInteger("id", 2).uniqueResult();System.out.println("书名:"+bookName);tx.commit();HibernateUtil.closeSession();}

控制台打印信息如下：

Hibernate: select book0_.name as col_0_0_ from book book0_条数：4=========Hibernate: select book0_.name as col_0_0_ from book book0_ where book0_.id=?书名:蓝血人

总结：

这里list查询出来的不是实体对象，所以这些数据不会存入缓存中（只有当list查询出的是实体对象时，才会被存入缓存中）

7）uniqueResult测试

@Testpublic void testUnique(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();Book book=(Book) session.createQuery("from Book where id=:id")  .setInteger("id", 2).uniqueResult();System.out.println("书名："+book.getName());System.out.println("=========");book=(Book) session.get(Book.class, 2);System.out.println("书名:"+book.getName());tx.commit();HibernateUtil.closeSession();}

控制台打印信息如下：

Hibernate: select book0_.id as id1_0_, book0_.author as author2_0_, book0_.name as name3_0_, book0_.price as price4_0_, book0_.pubDate as pubDate5_0_ from book book0_ where book0_.id=?书名：蓝血人=========书名:蓝血人

总结：

unique查数据不去缓存中查数据。

8）先list，再iterate

@Testpublic void testListIterate(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();List<Book> list=session.createQuery("from Book").list();System.out.println("条数："+list.size());System.out.println("=========");Iterator<Book> iter=session.createQuery("from Book").iterate();for(;iter.hasNext();){Book book=iter.next();System.out.println("书名："+book.getName());}tx.commit();HibernateUtil.closeSession();}

控制台打印信息如下：

Hibernate: select book0_.id as id1_0_, book0_.author as author2_0_, book0_.name as name3_0_, book0_.price as price4_0_, book0_.pubDate as pubDate5_0_ from book book0_条数：4=========Hibernate: select book0_.id as col_0_0_ from book book0_书名：读者书名：蓝血人书名：傲慢与偏见书名：中国历史

从上面示例可以看出iterate只查询了id，并没有查询实体类。iterate使用了缓存。

9）iterate

@Testpublic void testIterate(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();Iterator<Book> iter=session.createQuery("from Book").iterate();for(;iter.hasNext();){System.out.println("书名："+iter.next().getName());}System.out.println("=========");iter=session.createQuery("from Book").iterate();for(;iter.hasNext();){Book book=iter.next();System.out.println("书名："+book.getName());}tx.commit();HibernateUtil.closeSession();}

控制台打印信息如下：

Hibernate: select book0_.id as col_0_0_ from book book0_Hibernate: select book0_.id as id1_0_0_, book0_.author as author2_0_0_, book0_.name as name3_0_0_, book0_.price as price4_0_0_, book0_.pubDate as pubDate5_0_0_ from book book0_ where book0_.id=?书名：读者Hibernate: select book0_.id as id1_0_0_, book0_.author as author2_0_0_, book0_.name as name3_0_0_, book0_.price as price4_0_0_, book0_.pubDate as pubDate5_0_0_ from book book0_ where book0_.id=?书名：蓝血人Hibernate: select book0_.id as id1_0_0_, book0_.author as author2_0_0_, book0_.name as name3_0_0_, book0_.price as price4_0_0_, book0_.pubDate as pubDate5_0_0_ from book book0_ where book0_.id=?书名：傲慢与偏见Hibernate: select book0_.id as id1_0_0_, book0_.author as author2_0_0_, book0_.name as name3_0_0_, book0_.price as price4_0_0_, book0_.pubDate as pubDate5_0_0_ from book book0_ where book0_.id=?书名：中国历史=========Hibernate: select book0_.id as col_0_0_ from book book0_书名：读者书名：蓝血人书名：傲慢与偏见书名：中国历史

总结：

iterate会执行查询id的操作，当查询对象时，会检查缓存中是否存在。如果存在从缓存中取数据。iterate查询出来的对象也会放入缓存中。

管理一级缓存

flush()：强制将数据存入数据库表中；

clear()：清除缓存；

evict()：将对象从当前session中清除；

一级缓存很难管理，我们不一定知道什么时候该用flush，clear，evict，如果需要实时性很强的数据一般不用hibernate。

flush代码

@Testpublic void testSaveBatch(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();for(int i=0;i<10000;i++){Book book=new Book();book.setName("测试"+i);book.setPrice(21.5);book.setAuthor("读者出版传媒有限公司");book.setPubDate(new Date());if(i%50==0)session.flush();session.save(book);}tx.commit();HibernateUtil.closeSession();}

evict代码与clear效果相同

@Testpublic void testEvict(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();Book book=(Book) session.get(Book.class, 1);System.out.println(book.getName());//将book对象从session中清除（等同于session.clear()）session.evict(book);//清除缓存//session.clear();System.out.println("----------");book=(Book) session.get(Book.class, 1);System.out.println(book.getName());tx.commit();HibernateUtil.closeSession();}

控制台打印信息如下：

Hibernate: select book0_.id as id1_0_0_, book0_.author as author2_0_0_, book0_.name as name3_0_0_, book0_.price as price4_0_0_, book0_.pubDate as pubDate5_0_0_ from book book0_ where book0_.id=?读者----------Hibernate: select book0_.id as id1_0_0_, book0_.author as author2_0_0_, book0_.name as name3_0_0_, book0_.price as price4_0_0_, book0_.pubDate as pubDate5_0_0_ from book book0_ where book0_.id=?读者

2、二级缓存

SessionFactory：进程级别的缓存，支持集群。

使用步骤：

1）在hibernate.cfg.xml中配置（默认是开启的）

<!-- 使用二级缓存 --><property name="cache.use_second_level_cache">true</property>

2）配置cache.region.factory_class

<property name="cache.region.factory_class">org.hibernate.cache.ehcache.EhCacheRegionFactory</property>

3)导入ehcache的jar包

ehcache的jar包的地址是 hibernate-release-4.3.11.Final\lib\optional\ehcache

如图:

4)将ehcache的配置文件包放到src下

ehcache的配置文件的地址是 hibernate-release-4.3.11.Final\project\etc

如图：

ehcache.xml中部分属性的含义

5）在*.hbm.xml或在hibernate.cfg.xml中指定要使用二级缓存的类(推荐使用在hibernate.cfg.xml中指定)

    在Book.hbm.xml中指定

  在hibernate.cfg.xml中指定

6）测试

@Testpublic void testGet(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();Book book=(Book) session.get(Book.class, 1);//发出sql语句取数据System.out.println(book.getName());HibernateUtil.closeSession();session=HibernateUtil.getSession();System.out.println("============");book=(Book) session.get(Book.class, 1);System.out.println(book.getName());tx.commit();HibernateUtil.closeSession();}

控制台打印信息如下

Hibernate: select book0_.id as id1_0_0_, book0_.author as author2_0_0_, book0_.name as name3_0_0_, book0_.price as price4_0_0_, book0_.pubDate as pubDate5_0_0_ from book book0_ where book0_.id=?读者============读者

虽然我们关闭了session，又重新获得了一个session，但是获取第二个数据时，并没有去数据库查数据，说明二级缓存起作用了。

3、查询缓存

查询缓存是在二级缓存的基础上设置的，也就是说要使用查询缓存，我们需要先把二级缓存配置好，然后配置查询缓存

1）配置查询缓存

测试

@Testpublic void testQueryCache(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();List<Book> list=session.createQuery("from Book").setCacheable(true)  //使用查询缓存.list();System.out.println(list.size());System.out.println("-------");list=session.createQuery("from Book").setCacheable(true)  //使用查询缓存.list();System.out.println(list.size());tx.commit();HibernateUtil.closeSession();}

控制台打印信息如下：

Hibernate: select book0_.id as id1_0_, book0_.author as author2_0_, book0_.name as name3_0_, book0_.price as price4_0_, book0_.pubDate as pubDate5_0_ from book book0_4-------4

将session关闭，再重新打开仍然可以从二级缓存中使用查询缓存取出数据。

测试代码：

@Testpublic void testQueryCache(){Session session=HibernateUtil.getSession();Transaction tx=session.beginTransaction();List<Book> list=session.createQuery("from Book").setCacheable(true)  //使用查询缓存.list();System.out.println(list.size());HibernateUtil.closeSession();session=HibernateUtil.getSession();System.out.println("-------");list=session.createQuery("from Book").setCacheable(true)  //使用查询缓存.list();System.out.println(list.size());tx.commit();HibernateUtil.closeSession();}

控制台打印信息如下：

Hibernate: select book0_.id as id1_0_, book0_.author as author2_0_, book0_.name as name3_0_, book0_.price as price4_0_, book0_.pubDate as pubDate5_0_ from book book0_4-------4

说明数据存在二级缓存中，关闭session并不影响查询数据。

ehcache的jar包的地址是 hibernate-release-4.3.11.Final\lib\optional\ehcache