hibernate>二级缓存 小强斋

hibernate二级缓存

 

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

一、二级缓存的配置和使用：
 1、 将hibernate-3.2\etc\echcache.xml文件拷贝到src下
 2、开启二级缓存，修改hibernate.cfg.xml文件
     <property name="hibernate.cache.use_second_level_cache">true</property>
 3、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>
 4、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

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
	<class name="com.ncepu.hibernate.Student" table="t_student">
		
		<cache usage="read-only"/>
		        <id name="id">
			<generator class="native"/>
		</id>
		<property name="name"/>
		<many-to-one name="classes" column="classesid"/>
	</class>
</hibernate-mapping>

或在hibernate.cfg.xml文件中，采用<class-cache>标签

<class-cache class="com.ncepu.hibernate.Student" usage="read-only"/>

最终的hibernate.cfg.xml文件

<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
	<session-factory>
		<property name="hibernate.connection.url">jdbc:mysql://localhost/hibernate_cache</property>
		<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
		<property name="hibernate.connection.username">root</property>
		<property name="hibernate.connection.password">ncepu</property>
		<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
		<property name="hibernate.show_sql">true</property>
		
		<!-- 开启二级缓存 -->
		<property name="hibernate.cache.use_second_level_cache">true</property>
		
		<!-- 指定缓存产品提供商 -->
		<property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property>
		
		<mapping resource="com/ncepu/hibernate/Student.hbm.xml"/>
		
		<class-cache class="com.ncepu.hibernate.Student" usage="read-only"/>
	</session-factory>
</hibernate-configuration>

二、echcache.xml说明

1、echcache.xml中

  <defaultCache
        maxElementsInMemory="10000"
        eternal="false"
        timeToIdleSeconds="120"
        timeToLiveSeconds="120"
        overflowToDisk="true"
        />

The following attributes are required for defaultCache:

        name                              - Sets the name of the cache. This is used to identify the cache. It must be unique.
        maxInMemory                - Sets the maximum number of objects that will be created in memory
        eternal                            - Sets whether elements are eternal. If eternal,  timeouts are ignored and the element  is never expired.
        timeToIdleSeconds        - Sets the time to idle for an element before it expires. Is only used . if the element is not eternal. Idle time is now - last accessed time
        timeToLiveSeconds       - Sets the time to live for an element before it expires. Is only used.if the element is not eternal. TTL is now - creation time     
        overflowToDisk               - Sets whether elements can overflow to disk when the in-memory cache has reached the maxInMemory limit.

三、Test

1、二级缓存是缓存实体对象的，get()、load() 等方法都会使用。

/**
	 * 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);
		}
	}

2、sessionFactory管理二级缓存 

 factory.evict(Student.class, 1);

 factory.evict(Student.class);

/**
	 * 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);
		}
	}
	

3、一级缓存和二级缓存的交互 (了解即可)

/**
	 * 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);
		}
		
	}	

CacheMode参数用于控制具体的Session如何与二级缓存进行交互。

CacheMode.NORMAL - 从二级缓存中读、写数据。

CacheMode.GET - 从二级缓存中读取数据，仅在数据更新时对二级缓存写数据。

CacheMode.PUT - 仅向二级缓存写数据，但不从二级缓存中读数据。

CacheMode.REFRESH - 仅向二级缓存写数据，但不从二级缓存中读数据。