这是一个servlet实现的JMail.但是老是报错.

错误是(控制台打印出来的):

doGet()
doPost()
2008-9-17 17:43:24 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet jmail threw exception
java.lang.NoClassDefFoundError: javax/activation/DataSource
 at jmail.SendMail.doPost(SendMail.java:49)
 at jmail.SendMail.doGet(SendMail.java:29)

下面是那个servlet:

package jmail;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
import java.util.Properties;

import javax.mail.Message;
import javax.mail.Session;
import javax.mail.Transport;
import javax.activation.*;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class SendMail extends HttpServlet {
 private static final String CONTENT_TYPE="text/html;charset=GB2312";

 public void init() throws ServletException{
  System.out.println("init()");
 }
 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  System.out.println("doGet()");
  doPost(request,response);
 }

 public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  System.out.println("doPost()");
  response.setContentType(CONTENT_TYPE);
  PrintWriter out=response.getWriter();
  String smtpServer="163.com";
  String mailTo="fly20051987@yahoo.com.cn";
  String mailFrom="lqliw@yahoo.com.cn";
  String subject ="自己的信件";
  String body="内容为空的..";

  Properties p=new Properties();
  p.put("mail.transport.protocol", "smtp");
  p.put("mail.smtp.host",smtpServer);
  p.put("mail.mail.port", "25");
  Session session=Session.getDefaultInstance(p);
   
  Message mailMessage=new MimeMessage(session);
  try {
   mailMessage.setFrom(new InternetAddress(mailFrom));
   mailMessage.setRecipients(Message.RecipientType.TO, InternetAddress.parse(mailTo));
   mailMessage.setSentDate(new Date());
   mailMessage.setSubject(subject);
   mailMessage.setText(body);
  } catch (Exception e) {
   System.out.println("ERROR错误!!");
   e.printStackTrace();
  }
  Transport trans;
  try {
   trans=session.getTransport();
   trans.send(mailMessage);
   mailMessage.writeTo(System.out);
   System.out.println("邮件已经成功发送到:"+mailTo);
17_0612_7C272AC.rar

  } catch (Exception e) {
   e.printStackTrace();
  }
 }
}
另有一个附件,也就是这个工程.

请朋友指点一下,不胜感激...