Hibernate 在操作数据库的时候要执行很多操作，这些动作对用户是透明的。这些操作主要是有拦截器和时间组成

hibernate拦截器可以拦截大多数动作，比如事务开始之后（afterTransactionBegin）、事务完成之前（beginTransactionCompletion）、事务完成之后(afterTransactionCompletion)、持久化对象之前（onSave）,一个拦截器必须实现org.hibernate.Interceptor借口，hibernate提供了一个实现该借口的类EmptyInterceptor类

下面编写一个hibernate实例来说明hibernate拦截器的作用

首先编写一个保存持久化对象的信息类EntityInfo

public class EntityInfo {public Object entityBean;public Serializable id;public String[] properties;public Object getEntityBean() {return entityBean;}public void setEntityBean(Object entityBean) {entityBean = entityBean;}public Serializable getId() {return id;}public void setId(Serializable id) {this.id = id;}public String[] getProperties() {return properties;}public void setProperties(String[] properties) {this.properties = properties;}public String toString(){String info = "";if(entityBean !=null){info = entityBean.getClass().toString()+"\r\nid:"+id+"\r\n";if(properties != null){//处理properties中的所有元素for(String property:properties){//得到getter方法名try {String getter = "get" + property.substring(0, 1).toUpperCase()+property.substring(1);//使用反射技术和gettter方法名获得Method对象Method method = entityBean.getClass().getMethod(getter);//调用gettter方法，并追加生成要返回的信息info = info + property + ":" +method.invoke(entityBean).toString() +"\r\n";} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}}}return info;}
}

实现拦截器类，代码如下

public class EntityBeanInterceptor extends EmptyInterceptor {private ThreadLocal entityBeans = new ThreadLocal();@Overridepublic void afterTransactionBegin(Transaction tx){entityBeans.set(new HashSet<EntityInfo>());}@Overridepublic void afterTransactionCompletion(Transaction tx){if(tx.wasCommitted()){Iterator i =  ((Collection)entityBeans.get()).iterator();while (i.hasNext()) {//在提交事务之后输出试题bean的内容EntityInfo info = (EntityInfo) i.next();//调用方法数据EntityBean对象processEntityBean(info);}}}private void processEntityBean(EntityInfo info){System.out.println(info);}@Overridepublic boolean onSave(Object entity,Serializable id, Object[] state,String[] propertyNames,Type[] types){EntityInfo info = new EntityInfo();info.entityBean = entity;info.properties = propertyNames;info.id =id;//在持久化对象后，将对象信息保存到当前线程的HashSet<EntityInfo>对象中((HashSet<EntityInfo>) entityBeans.get()).add(info);return false;}}

注册拦截器类，本例中在构造Session时创建拦截器类

public class HibernateSessionFactory {/*其他代码省略*/private static ThreadLocal threadLocal = new ThreadLocal();private  static Configuration configuration = new Configuration();private static org.hibernate.SessionFactory sessionFactory;public static Session getSession(Interceptor... interceptor){Session session = (Session) threadLocal.get();if(session == null || !session.isOpen()){//如果session为空重新建立一个Session工厂if(sessionFactory == null){rebuildSessionFactory();}//如果interceptor参数值中包含拦截器对象，则安装该拦截器session = (sessionFactory != null)?((interceptor.length == 0)?sessionFactory.openSession():sessionFactory.openSession(interceptor[0])):null;//如果ThreadLocal对象中没有属于当前线程的session对象，则添加一个Session对象threadLocal.set(session);}}}

测试拦截器类

public class TestInterceptor {private void mian() {
// TODO Auto-generated method stub
Session session = HibernateSessionFactory.getSession(new EntityBeanInterceptor());
Transaction tx = session.beginTransaction();
//Customer是一个实体bean
Customer customer = new Customer();
customer.setName("hqw");
session.saveOrUpdate(customer);
tx.commit();
session.close();
}
}

这样在构造session时就注册了拦截器，应为本文在EntityInterceptor类中注册了在事务开始后、事务完成后、持久化后三个方法，所以在相应地方就会调用拦截器中的方法