应用程序能够响应Hibernate内部产生的特定事件是非常有用的。这样就允许实现某些通用的功能以及允许对Hibernate功能进行扩展
持久层框架底层的拦截器机制是对诸如Spring等业务管理容器拦截机制的有益补充,使得我们可以在更低层次、更广的对象范围上进行AOP操作(Spring虽然将Hibernate纳入到了其容器管理的范围内,但是并没有途径实现对其实体对象的管理)。这样就允许实现某些通用的功能,以及允许对Hibernate功能进行扩展。
1、拦截器(Interceptors)
Interceptor接口提供了从会话(session)回调(callback)应用程序(application)的机制,这种回调机制可以允许应用程序在持久化对象被保存、更新、删除或是加载之前,检查并(或)修改其属性。
你可以直接实现Interceptor接口,也可以(最好)继承自EmptyInterceptor。
拦截器可以有两种:
- session范围内的
- sessionFactory范围内的
使用拦截器时按如下步骤:
(1)定义实现Interceptor接口的拦截器类
(2)通过session启用拦截器,或者通过Configuration启用全局拦截器
当使用某个重载的SessionFactory.openSession()使用Interceptorzuowei参数调用打开一个session的时候,就指定了Session范围内的拦截器。
Session session = factory.openSession(new AuditInterceptor());
SessionFactory范围内的拦截器要通过Configuration中注册,而这必须在创建SessionFactory之前。在这种情况下,给出的拦截器会被这个SessionFactory所打开的所有session使用了,除非session打开时明确指明了使用的拦截器。SessionFactory范围内的拦截器,必须是线程安全的,因为多个session可能并发使用这个拦截器,要因此小心不要保存与session相关的状态。具体配置
new Configuration().setInterceptor(new AuditInterceptor());
2、事件系统(Event system)
- 如果需要响应持久层的某些特殊事件,你也可以使用Hibernate3的事件框架。该事件系统可以用来替代拦截器,也可以作为拦截器的补充来使用。
-基本上,session接口的每个方法都有相对应的事件。比如LoadEvent,FlushEvent,等等(可以查阅XML配置文件的DTD以及org.hibernate.event包来获得所有已定义的事件的列表)。
- 当某个方法被调用时,hibernate Session会生成一个相应的事件并激活所有配置好的事件监听器(观察者模式)。被监听的方法所做的其实仅仅是激活监听器,”实际“的工作是由监听器完成的。你可以自由的选择实现一个自己定制的监听器:比如,实现并注册用来处理处理LoadEvent的LoadeventListener接口,来处理所有的调用Session的load()方法的请求。
- 监听器在运行时被实例化为单例(singleton)对象,也就是说,所有同类型的事件的处理共享同一个监听器实例,因此监听器不应该保存任何与请求相关的状态。
- 用户定制的监听器需要实现相关的事件监听器接口,或者从一个适合的基类继承(甚至是从Hibernate自带的默认事件监听器类继承。
- 用户定制的监听器可以通过编程使用Configuration对象来注册,也可以在Hibernate的XML格式的配置文件中进行声明。
- 你还需要修改一处配置,来告诉Hibernate,除了默认监听器,还要附加选定的监听器。
<session-factory> <event type="laod"> <listener class="com.cdtax.MyLoadListener"/> <listener class="org.hibernate.event.def.DefaultLoadEventListener"/> </event>
通过编程的方式注册
Configuration cfg = new Configuration(); LoadEventListener[] stack = {new MyLoadListener(),new DefaultLoadEventListener()}; cfg.getEventListeners().setLoadEventListeners(stack);
- 通过在XML配置文件声明而注册的监听器不能共享实例,如果在多个<lsitener/>节点中使用了相同的类的名字,而每一个引用都会产生一个独立的实例,如果你需要在多个监听器类型之间共享监听器的实例,则你必须使用编程的方式来进行注册。
3、关于配置文件中id标签的generator
有UUID,foreign等
4、拦截器举例:
import java.sql.Date; import java.sql.Timestamp; public class People { private Long id; private String username; private String password; private int telphone; private char gender; //'M','F' private boolean graduation; private Date birthday; private Timestamp marryTime; private byte[] file; public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public int getTelphone() { return telphone; } public void setTelphone(int telphone) { this.telphone = telphone; } public char getGender() { return gender; } public void setGender(char gender) { this.gender = gender; } public boolean isGraduation() { return graduation; } public void setGraduation(boolean graduation) { this.graduation = graduation; } public Date getBirthday() { return birthday; } public void setBirthday(Date birthday) { this.birthday = birthday; } public Timestamp getMarryTime() { return marryTime; } public void setMarryTime(Timestamp marryTime) { this.marryTime = marryTime; } public byte[] getFile() { return file; } public void setFile(byte[] file) { this.file = file; } }
映射文件:
<?xml version="1.0" encoding="UTF-8"?> <!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.cdtax.hibernate.People" table="people"> <id name="id" column="id" type="long"> <generator class="increment"></generator> </id> <property name="username" column="username" type="string"></property> <property name="password" column="password" type="string"></property> <property name="telphone" column="telphone" type="int"></property> <property name="gender" column="gender" type="character"></property> <property name="graduation" column="graduation" type="boolean"></property> <property name="birthday" column="birthday" type="date"></property> <property name="marryTime" column="marryTime" type="timestamp"></property> <property name="file" column="file" type="binary"></property> </class> </hibernate-mapping>
创建数据库表
create table people (id bigint not null, username varchar(255), password varchar(255), telphone integer, gender char(1), graduation bit, birthday date, marryTime datetime, file tinyblob, primary key (id))
创建拦截器:
import java.io.Serializable; import java.util.Iterator; import org.hibernate.EmptyInterceptor; import org.hibernate.Transaction; import org.hibernate.type.Type; public class TestInterceptor extends EmptyInterceptor { @Override public boolean onLoad(Object entity, Serializable id, Object[] state, String[] propertyNames, Type[] types) { System.out.println("onLoad invoked!"); for(String propertyName : propertyNames) { System.out.println(propertyName); } return true; } @Override public boolean onSave(Object entity, Serializable id, Object[] state, String[] propertyNames, Type[] types) { System.out.println("onsave invoked!"); for(String propertyName : propertyNames) { System.out.println(propertyName); } return true; } @Override public void onDelete(Object entity, Serializable id, Object[] state, String[] propertyNames, Type[] types) { System.out.println("onDelete invoked!"); for(String propertyName : propertyNames) { System.out.println(propertyName); } } @Override public boolean onFlushDirty(Object entity, Serializable id, Object[] currentState, Object[] previousState, String[] propertyNames, Type[] types) { System.out.println("onFlushDirty invoked!"); for(String propertyName : propertyNames) { System.out.println(propertyName); } return true; } @Override public void postFlush(Iterator entities) { System.out.println("postflush invkked!"); } @Override public void beforeTransactionCompletion(Transaction tx) { System.out.println("beforeTanscationCompletion invoked!"); } @Override public void afterTransactionBegin(Transaction tx) { System.out.println("afterTransactionBegin invoked"); } }
我们的拦截器直接继承自Hibernate的EmptyInterceptor,然后我们覆盖其提供的方法即可。
方法中的参数Object entity就是我们要操作的对象,如这里就是People对象。propertyNames是操作对象的属性名的数组。onLoad方法就是在加载对象的时候执行方法,onSave方法就是在保存对象的时候执行。关于flush,清空缓存,当对象为脏数据时,或者事务提交的时候。
测试:
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.sql.Timestamp;
import java.util.Iterator;
import java.util.List;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import com.cdtax.interceptor.TestInterceptor;
public class HibernateTest
{
private static SessionFactory sessionFactory;
static
{
try
{
sessionFactory = new Configuration().configure().buildSessionFactory();
}
catch(Exception ex)
{
ex.printStackTrace();
}
}
public static void main(String[] args) throws Exception
{
People people = new People();
people.setUsername("zhangsan1");
people.setPassword("223456");
people.setGender('M');
people.setBirthday(new java.sql.Date(new java.util.Date().getTime()));
people.setGraduation(true);
people.setTelphone(1234);
people.setMarryTime(new Timestamp(new java.util.Date().getTime()));
InputStream is = new FileInputStream("c:/RHDSetup.log");
int length = is.available();
byte[] buffer = new byte[length];
is.read(buffer);
people.setFile(buffer);
Session session = sessionFactory.openSession(new TestInterceptor());
Transaction tx = null;
try
{
tx = session.beginTransaction();
session.save(people);
tx.commit();
}
catch(Exception ex)
{
if(null != tx)
{
tx.rollback();
}
}
finally
{
session.close();
}
}
}
这是session范围的拦截器,执行的结果
Hibernate: select max(id) from people
onsave invoked!
username
password
telphone
gender
graduation
birthday
marryTime
file
Hibernate: insert into people (username, password, telphone, gender, graduation, birthday, marryTime, file, id) values (?, ?, ?, ?, ?, ?, ?, ?, ?)
postflush invkked!
beforeTanscationCompletion invoked!
afterTransactionBegin invoked
红色部分是session.save(people);这一句产生的,可以看到在save时,先执行拦截器onSave方法,然后执行insert语句执行数据库插入。然后在事务提交后,执行postFlush方法,在事务结束前后分别在调用beforeTransactionCompletion和afterTransactionCompletion
然后进行查询加载测试:
try { tx = session.beginTransaction(); People p = (People)session.get(People.class, new Long(1)); System.out.println(p.getUsername()); tx.commit(); }
Hibernate: select people0_.id as id0_0_, people0_.username as username0_0_, people0_.password as password0_0_, people0_.telphone as telphone0_0_, people0_.gender as gender0_0_, people0_.graduation as graduation0_0_, people0_.birthday as birthday0_0_, people0_.marryTime
as marryTime0_0_, people0_.file as file0_0_ from people people0_ where people0_.id=?
onLoad invoked!
username
password
telphone
gender
graduation
birthday
marryTime
file
zhangsan1
postflush invkked!
beforeTanscationCompletion invoked!
afterTransactionBegin invoked
这次调用了拦截器的onLoad方法。
5、事件(监听器)
拦截器能够实现的功能,事件(监听器同样能够完成),编写两个两个监听器:
import java.io.Serializable; import org.hibernate.event.SaveOrUpdateEvent; import org.hibernate.event.def.DefaultSaveEventListener; public class TestSaveListener extends DefaultSaveEventListener { @Override protected Serializable performSaveOrUpdate(SaveOrUpdateEvent event) { System.out.println("performSaveOrUpdate invoked!!!!"); return super.performSaveOrUpdate(event);//必须显式的调用一下父类的方法,否则Hibernate的相关机制都被覆盖掉了 } }
import org.hibernate.HibernateException; import org.hibernate.event.LoadEvent; import org.hibernate.event.def.DefaultLoadEventListener; public class TestLoadListener extends DefaultLoadEventListener { @Override public void onLoad(LoadEvent arg0, LoadType arg1) throws HibernateException { super.onLoad(arg0, arg1); //必须显式的调用一下父类的方法,否则Hibernate的相关机制都被覆盖掉了 System.out.println("onLoad invoked!!!"); System.out.println(arg0.getEntityId() + "," + arg0.getEntityClassName()); } }
这里需要注意,在重写方法时,一定要显式的调用一下父类的方法,否则Hibernate的相关机制就被你覆盖了,Hibernate就不起作用了。
编写完监听器需要部署到配置文件中hibernate.cfg.xml中
<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<!-- Generated by MyEclipse Hibernate Tools. -->
<hibernate-configuration>
<session-factory>
<property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>
<property name="connection.username">root</property>
<property name="connection.password">root</property>
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>
<property name="show_sql">true</property>
<mapping resource="People.hbm.xml" />
<event type="load">
<listener class="com.cdtax.event.TestLoadListener"/>
</event>
<event type="save">
<listener class="com.cdtax.event.TestSaveListener"/>
</event>
</session-factory>
</hibernate-configuration>
执行上面的保存测试程序,结果:
performSaveOrUpdate invoked!!!!
Hibernate: select max(id) from people
onsave invoked!
username
password
telphone
gender
graduation
birthday
marryTime
file
Hibernate: insert into people (username, password, telphone, gender, graduation, birthday, marryTime, file, id) values (?, ?, ?, ?, ?, ?, ?, ?, ?)
postflush invkked!
beforeTanscationCompletion invoked!
afterTransactionBegin invoked
可以看到执行了事件监听器方法,同时也执行了拦截器方法。
执行上面查询加载的测试,执行结果:
Hibernate: select people0_.id as id0_0_, people0_.username as username0_0_, people0_.password as password0_0_, people0_.telphone as telphone0_0_, people0_.gender as gender0_0_, people0_.graduation as graduation0_0_, people0_.birthday as birthday0_0_, people0_.marryTime
as marryTime0_0_, people0_.file as file0_0_ from people people0_ where people0_.id=?
onLoad invoked!
username
password
telphone
gender
graduation
birthday
marryTime
file
onLoad invoked!!!
1,com.cdtax.hibernate.People
zhangsan1
postflush invkked!
beforeTanscationCompletion invoked!
afterTransactionBegin invoked
拦截器与事件监听器的区别:
事件的监听器还有另一种配制方法:
在hibernate.cfg.xml中直接配置<listener>标签:
<listener class="com.cdtax.event.TestSaveListener" type="save"/>