<%
  Element root= null;
  Element student= null;
  Element number= null;
  Element name= null;
  Element age= null;

  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"));   
     %>

------解决方案--------------------
错误信息贴出来

------解决方案--------------------
org.apache.jasper.JasperException: /index.jsp(2,0) Page directive must not have multiple occurrences of pageencoding

index.jsp第二行是不是又引入<%@ page language="java" import="org.jdom.*" pageEncoding="GBK"%>了，只能设定一次编码。

------解决方案--------------------
方法中用到包的方法都没有报错，说明包肯定导进去了