import java.lang.*;

import org.jdom.*;

import org.jdom.output.*;

import org.jdom.input.*;

public class WriteXML

{

    public void BuildXML() throws Exception

    {

        Element root,student,number,name,age;

        root = new Element("student-info"); //生成根元素：student-info   

        student = new Element("student");      //生成元素：student,该元素中将包含元素number,name,age

        number = new Element("number");

        name = new Element("name");

        age = new Element("age");

        Document doc = new Document(root);    //将根元素植入文档doc中

        number.setText("001");

        name.setText("lnman");

        age.setText("24");

        student.addContent(number);

        student.addContent(name);

        student.addContent(age);

        root.addContent(student);

        Format format = Format.getCompactFormat();

        format.setEncoding("gb2312");           //设置xml文件的字符为gb2312

        format.setIndent("    ");               //设置xml文件的缩进为4个空格

        XMLOutputter XMLOut = new XMLOutputter(format);//在元素后换行，每一层元素缩排四格

        XMLOut.output(doc, new FileOutputStream("studentinfo.xml"));  

    }

    public static void main(String[] args) throws Exception

    {

        WriteXML w = new WriteXML();

        System.out.println("Now we build an XML document .....");

        w.BuildXML();

        System.out.println("finished!");

    }

}

javac时不出错，
java后出现的错误如下：Exception in thead "main" java.lang.NoClassDefFoundError:org/jdom/Content
我想了好几天还是无法解决，请各位帮忙，谢了。