hibernate初学者碰到的问题，请高手指教

高手指教啊。 郁闷好久了。错误描述
2006-1-20 10:34:24 net.sf.hibernate.cfg.Environment <clinit>
信息: Hibernate 2.1.7
2006-1-20 10:34:24 net.sf.hibernate.cfg.Environment <clinit>
信息: loaded properties from resource hibernate.properties: {hibernate.cglib.use_reflection_optimizer=true}
2006-1-20 10:34:24 net.sf.hibernate.cfg.Environment <clinit>
信息: using CGLIB reflection optimizer
2006-1-20 10:34:24 net.sf.hibernate.cfg.Environment <clinit>
信息: using JDK 1.4 java.sql.Timestamp handling
2006-1-20 10:34:24 net.sf.hibernate.cfg.Configuration addClass
信息: Mapping resource: com/aaok/blog/dao/Content.hbm.xml
2006-1-20 10:34:24 net.sf.hibernate.cfg.Binder bindRootClass
信息: Mapping class: com.aaok.blog.dto.Content -> content
Exception in thread "main" java.lang.NoClassDefFoundError: net/sf/cglib/beans/BulkBeanException
        at net.sf.hibernate.util.ReflectHelper.getBulkBean(ReflectHelper.java:180)
        at net.sf.hibernate.type.ComponentType.<init>(ComponentType.java:111)
        at net.sf.hibernate.cfg.Binder.bindComponent(Binder.java:911)
        at net.sf.hibernate.cfg.Binder.bindRootClass(Binder.java:282)
        at net.sf.hibernate.cfg.Binder.bindRoot(Binder.java:1257)
        at net.sf.hibernate.cfg.Configuration.add(Configuration.java:252)
        at net.sf.hibernate.cfg.Configuration.addInputStream(Configuration.java:288)
        at net.sf.hibernate.cfg.Configuration.addClass(Configuration.java:354)
        at com.aaok.blog.dao.FindContentByIDDAOHibernate.FindContentBYID(FindContentByIDDAOHibernate.java:21)
        at com.aaok.blog.dao.FindContentByIDDAOHibernate.main(FindContentByIDDAOHibernate.java:42)
执行的文件
package com.aaok.blog.dao;
import java.util.List;
import net.sf.hibernate.*;
import net.sf.hibernate.cfg.Configuration;
//import com.aaok.blog.dto.Content;
public class FindContentByIDDAOHibernate  {        public void FindContentBYID() throws HibernateException {
                
//                System.out.println("23222222222222"+"what id is?"+ID);
                List list = null;
                Content content = new Content();
                StringBuffer sb = new StringBuffer();
//                sb.append(" from content,BlogItem where content.contentID='"+ID+"'");
                
                
                System.out.println(sb);
        
                Configuration config=new Configuration();
                config.addClass(Content.class);
                SessionFactory sf = config.buildSessionFactory();
                Session session = sf.openSession();
                Transaction tx = session.beginTransaction();
                tx.commit();
                session.close();
        }        public static void main(String[] arg) throws HibernateException{
                
         FindContentByIDDAOHibernate FC= new FindContentByIDDAOHibernate();
         FC.FindContentBYID();        }}content.java文件
package com.aaok.blog.dao;import java.io.Serializable;
import java.util.List;import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;
import org.apache.commons.lang.builder.ToStringBuilder;/** 
*        @hibernate.class
*         table="content"
*     
*/
public class Content implements Serializable {    /** identifier field */
    private String contentId;    /** identifier field */
    private String content;    /** identifier field */
    private String abstracts;
    
    private List list;    /** full constructor */
    public Content(String contentId, String content, String abstracts) {
        this.contentId = contentId;
        this.content = content;
        this.abstracts = abstracts;
    }    /** default constructor */
    public Content() {
    }    /** 
     *                @hibernate.property
     *                 column="contentID"
     *             
     */
    public String getContentId() {
        return this.contentId;
    }    public void setContentId(String contentId) {
        this.contentId = contentId;
    }    /** 
     *                @hibernate.property
     *                 column="content"
     *             
     */
    public String getContent() {
        return this.content;
    }    public void setContent(String content) {
        this.content = content;
    }    /** 
     *                @hibernate.property
     *                 column="abstract"
     *             
     */
    public String getAbstract() {
        return this.abstracts;
    }    public void setAbstract(String abstracts) {
        this.abstracts = abstracts;
    }    public String toString() {
        return new ToStringBuilder(this)
            .append("contentId", getContentId())
            .append("content", getContent())
            .append("abstract", getAbstract())
            .toString();
    }    public boolean equals(Object other) {
        if ( !(other instanceof Content) ) return false;
        Content castOther = (Content) other;
        return new EqualsBuilder()
            .append(this.getContentId(), castOther.getContentId())
            .append(this.getContent(), castOther.getContent())
            .append(this.getAbstract(), castOther.getAbstract())
            .isEquals();
    }    public int hashCode() {
        return new HashCodeBuilder()
            .append(getContentId())
            .append(getContent())
            .append(getAbstract())
            .toHashCode();
    }        /**
         * @param list
         */
        public void setList(List list) {
                // TODO 自动生成方法存根
                
        }
        
        public List getList(){
                return this.list;
                
        }
        }
content.hbm.xml文件
<?xml version="1.0"?>    
<hibernate-mapping><class 
    name="com.aaok.blog.dto.Content" 
    table="content"
>
    <meta attribute="class-description" inherit="false">
       @hibernate.class
        table="content"
    </meta>    <composite-id>
        <meta attribute="field-description" inherit="false">
           @hibernate.id
            generator-class="assigned"
        </meta>
        <key-property 
            name="contentId" 
            column="contentID" 
            type="java.lang.String"
            length="13"
        >
            <meta attribute="field-description">
               @hibernate.property
                column="contentID"
            </meta> 
        </key-property>
        <key-property 
            name="content" 
            column="content" 
            type="java.lang.String"
            length="65535"
        >
            <meta attribute="field-description">
               @hibernate.property
                column="content"
            </meta> 
        </key-property>
        <key-property 
            name="abstract" 
            column="abstract" 
            type="java.lang.String"
            length="65535"
        >
            <meta attribute="field-description">
               @hibernate.property
                column="abstract"
            </meta> 
        </key-property>
    </composite-id>    
    <!-- Associations -->
    <!-- derived association(s) for compound key -->
    <!-- end of derived association(s) -->
  </class>
</hibernate-mapping>