Hibernate 创建SessionFactory失败，怎么回事？

public class HibernateUtil {

private static final SessionFactory sessionFactory;

static {
try {
Configuration config = new Configuration().configure();
sessionFactory = config.buildSessionFactory();// 执行到这步就出错了
} catch (Throwable ex) {
ex.printStackTrace();

throw new ExceptionInInitializerError(ex);


}
}

public static final ThreadLocal session = new ThreadLocal();

public static Session currentSession() throws HibernateException {
Session s = (Session) session.get();
// Open a new Session, if this Thread has none yet
if (s == null||!s.isOpen()) {
s = sessionFactory.openSession();

session.set(s);
}
return s;
}

public static void closeSession() throws HibernateException {
Session s = (Session) session.get();
session.set(null);
if (s != null)
s.close();
}
}

该怎么解决？

[解决办法]
信息: validateJarFile(D:\Program Files\Tomcat 5.5\webapps\studentInfo\WEB-INF\lib\servlet.jar) - jar not loaded. See Servlet Spec 2.3, section 9.7.2. Offending class: javax/servlet/Servlet.class


servlet.jar删了

然后把你web.xml帖出来看看。
[解决办法]
<property name= "hibernate.connection.url "> jdbc:mysql:///ff </property>
这是什么啊？