Configuration config = new Configuration();报错java.lang.NoClassDefFoundError: org/dom4j/DocumentException

[yuanye2008]

import org.hibernate.cfg.Configuration;

程序运行到
Configuration config = new Configuration();
报错!错误如下:

Exception in thread "main" java.lang.NoClassDefFoundError: org/dom4j/DocumentException
at hibernatetest.HibernateFactory.createConfiguration(HibernateFactory.java:10)
at hibernatetest.Test.main(Test.java:10)
什么原因造成的?