麻烦了。。帮我看看！
jap：
<input type="submit" name="Submit" id="a" value="保存" />
<input type="submit" name="Submit" id="b" value="修改" />
<input type="submit" name="Submit" id="c" value="删除" />
servlet：
String value=(String)request.getParameter("submit");
if(value.equals("保存"))
{response.sendRedirect("a.jsp");}
else if(value.equals("修改"))
{response.sendRedirect("b.jsp");}
else
{response.sendRedirect("c.jsp");}
试了很久都是说错误：
type Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
java.lang.NullPointerException
luru.luruxiugai.doPost(luruxiugai.java:82)
javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.13 logs.
问题1.
如何通过RandomAccessFile类的seek()方法将指针移动到文件末尾，再用writeChars(String s)将数据写入某个文档文件
问题2.
StringTokenizer是什么东西，干嘛用的？
由于小弟初学js ......
