I follows examples of :
http://www.hibernate.org.cn:8000/65.html
And just can't run with "net.sf.hibernate.MappingException: could not instantiate id generator", I search the web and google forum, and got no luck, I am new to hibernate and not know what 's going on, wish you
could help.


Hibernate version:
hibernate-2.1.7c

Mapping documents:
file:///C:/hibernate-mapping-2.0.dtd is extracted from hibernate-2.1.7c .zip released
---------------------------------------------------------------------------------
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD//EN"
"file:///C:/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
<class name="com.javamodel.hibernate.Person" table="person">
<id name="id">
<generator class="vm.long"/>
</id>
<property name="email"/>
<property name="name"/>
</class>

</hibernate-mapping>
<!-- parsed in 0ms -->
---------------------------------------------------------------------------------

Code between sessionFactory.openSession() and session.close():
---------------------------------------------------------------------------------
package com.javamodel.hibernate;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Properties;
import net.sf.hibernate.HibernateException;
import net.sf.hibernate.MappingException;
import net.sf.hibernate.Session;
import net.sf.hibernate.SessionFactory;
import net.sf.hibernate.Transaction;
import net.sf.hibernate.cfg.Configuration;

public class Example
{

private static SessionFactory _sessions = null;
private static Properties pops = new Properties();

static {
try
{

InputStream stream = Thread.currentThread().getContextClassLoader().getResource("hibernate.properties").openStream();//Example.class.getResourceAsStream("hibernate.properties");
try
{
pops.load(stream);
}
catch (IOException e1)
{
e1.printStackTrace();
}
Configuration cfg = new Configuration();
cfg.addClass(Person.class);
cfg.setProperties(pops);
_sessions = cfg.buildSessionFactory();
if (_sessions == null)
{
System.out.println("This _session is nULLL");
}
}
catch (MappingException e)
{
e.printStackTrace();
}
catch (HibernateException e)
{
e.printStackTrace();
}
catch (Exception e)
{
e.printStackTrace();
}

}

public static void main(String[] args) throws HibernateException
{

Person person = new Person();
person.setName("smallduzi");
person.setEmail("smallduzi@sohu.com");

Session session = _sessions.openSession();

Transaction tx = null;
try
{
tx = session.beginTransaction();
session.save(person);
tx.commit();
}
catch (HibernateException he)
{
if (tx != null)
tx.rollback();
throw he;
}
finally
{
session.close();
}

}

}

---------------------------------------------------------------------------------

Full stack trace of any exception that occurs:
---------------------------------------------------------------------------------
net.sf.hibernate.MappingException: could not instantiate id generator
at net.sf.hibernate.id.IdentifierGeneratorFactory.create(IdentifierGeneratorFactory.java:82)
at net.sf.hibernate.mapping.SimpleValue.createIdentifierGenerator(SimpleValue.java:82)
at net.sf.hibernate.persister.AbstractEntityPersister.<init>(AbstractEntityPersister.java:645)
at net.sf.hibernate.persister.EntityPersister.<init>(EntityPersister.java:692)
at net.sf.hibernate.persister.PersisterFactory.createClassPersister(PersisterFactory.java:42)
at net.sf.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:137)
at net.sf.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:796)
at com.javamodel.hibernate.Example.<clinit>(Example.java:37)
Caused by: net.sf.hibernate.MappingException: Dialect does not support sequences
at net.sf.hibernate.dialect.Dialect.getSequenceNextValString(Dialect.java:327)
at net.sf.hibernate.id.SequenceGenerator.configure(SequenceGenerator.java:57)
at net.sf.hibernate.id.IdentifierGeneratorFactory.create(IdentifierGeneratorFactory.java:78)
... 7 more
java.lang.NullPointerException
at com.javamodel.hibernate.Example.main(Example.java:65)
Exception in thread "main"
---------------------------------------------------------------------------------

Name and version of the database you are using:
IBM DB2 with Websphere

The generated SQL (show_sql=true):

Debug level Hibernate log excerpt:

Thank you

I change:

<id name="id">
<generator class="vm.long"/>
</id>
or
<id name="id">
<generator class="sequence"/>
</id>

in mapping file into:

<id name="id" type="string">
<generator class="vm"/>
</id>

and everything goes OK now.

Sorry but thank you.