第一个hibernate例子失败

User.hbm.xml中<?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">
<!--
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="com.lee.hibernate.User" table="user" catalog="test">
        <composite-id name="id" class="com.lee.hibernate.UserId">
            <key-property name="id" type="java.lang.Integer">
                <column name="ID" />
            </key-property>
            <key-property name="name" type="java.lang.String">
                <column name="NAME" length="50" />
            </key-property>
            <key-property name="password" type="java.lang.String">
                <column name="PASSWORD" length="50" />
            </key-property>
            <key-property name="firstName" type="java.lang.String">
                <column name="FIRST_NAME" length="50" />
            </key-property>
            <key-property name="lastName" type="java.lang.String">
                <column name="LAST_NAME" length="50" />
            </key-property>
            <key-property name="dateCreated" type="java.util.Date">
                <column name="DATE_CREATED" length="0" />
            </key-property>
        </composite-id>
    </class>
</hibernate-mapping>

程序运行后显示
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Exception in thread "main" java.lang.ClassCastException: java.lang.Integer
at org.hibernate.type.ComponentType.toLoggableString(ComponentType.java:377)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:112)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:187)
at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:33)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:172)
at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:27)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:535)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:523)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:519)
at com.lee.hibernate.UserDAO.save(UserDAO.java:30)
at com.lee.hibernate.HibernateExample.addUser(HibernateExample.java:22)
at com.lee.hibernate.HibernateExample.main(HibernateExample.java:8)
大哥们帮忙！

在src里面添加log4j.properties
内容是:
log4j.rootLogger=WARN, Console

log4j.appender.Console=org.apache.log4j.ConsoleAppender
log4j.appender.Console.layout=org.apache.log4j.PatternLayout
log4j.appender.Console.layout.ConversionPattern=(%r ms) [%t] %-5p: %c#%M %x: %m%n

log4j.logger.com.genuitec.eclipse.sqlexplorer=DEBUG
log4j.logger.org.apache=WARN
log4j.logger.org.hibernate=WARN

java.lang.ClassCastException: java.lang.Integer

为什么只在修改操作的时候才出现这个问题呢？？