为什么我用JAVAMAIL写的发送邮件的程序，接收后附件的名字老是出现的是乱码呢？附原代码，大家帮忙看看

<%@ page contentType="text/html;charset=gb2312" %>
<%@ page import="java.io.*"%>
<%@ page import="java.util.*"%>
<%@ page import="java.sql.*"%> 
<%@ page import="javax.servlet.*"%> 
<%@ page import="javax.servlet.http.*"%> 
<%@ page import="javax.mail.*, javax.mail.internet.*, javax.activation.*,"%>
<%@ page import="java.net.*"%>  
<%@ page import="java.util.*, java.text.*" %> 
<%@ page session="true"%>
<html><!-- InstanceBegin template="/Templates/ok.dwt.jsp" codeOutsideHTMLIsLocked="false" -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
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<title>:::{Welcome to you!}:::</title>
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</head><body leftmargin="0" topmargin="200">
<div align="center">
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try{
    //获得参数
  
  String username=session.getValue("username").toString();
  String password=session.getValue("password").toString();
 
  
  String subject=new String(request.getParameter("subject").trim().getBytes("ISO-8859-1"),"GBK");
  String text=new String(request.getParameter("text").trim().getBytes("ISO-8859-1"),"GBK");
  String to=new String(request.getParameter("to").trim().getBytes("ISO-8859-1"),"GBK");
          
    Properties props = new Properties();
    Session sendMailSession;
    Transport transport;
    sendMailSession = Session.getInstance(props, null);
   
    props.put("mail.smtp.host", "192.168.0.3"); 
    props.put("mail.smtp.auth", "true");  //允许smtp校验    transport = sendMailSession.getTransport("smtp");
    transport.connect("192.168.0.3",username,password);  //你的用户名,密码...........
   
    
    MimeMessage mimeMsg = new MimeMessage(sendMailSession); //创建MIME邮件对象 
    Multipart mp = new MimeMultipart();  //Multipart对象,邮件内容,标题,附件等内容均添加到其中后再生成MimeMessage对象 
    
    
    //设置mail主题
   String mail_subject=subject;
   mimeMsg.setSubject(mail_subject);
   
   //设置发信人地址
   String strFrom=username+"@"+"gdnanhai.gov.cn";
   strFrom=new String(strFrom.getBytes(),"8859_1");
   mimeMsg.setFrom(new InternetAddress(strFrom));
         
   
   
   //设置收件人地址
   mimeMsg.setRecipients(Message.RecipientType.TO, InternetAddress.parse(to));    
   
   //设置mail正文
   String mail_text= text;
   mimeMsg.setSentDate(new java.util.Date());   
   BodyPart bp1 = new MimeBodyPart(); 
   bp1.setContent("<meta http-equiv=Content-Type content=text/html; charset=gb2312>"+mail_text,"text/html;charset=GB2312"); 
   mp.addBodyPart(bp1); 
   
   
    //设置附件(mime方式)
   String filepath="D:\\bea2\\user_projects\\hyf\\applications\\DefaultWebApp\\upload\\";
   String filename;   
   filename=session.getValue("file1").toString().trim(); 
   out.println(filename);
    if(!filename.equals(""))
    {
   FileDataSource fileds = new FileDataSource(filepath+filename); 
   BodyPart bp = new MimeBodyPart();
   bp.setDataHandler(new DataHandler(fileds)); 
   bp.setFileName(new String(fileds.getName().toString().trim().getBytes("ISO-8859-1"),"GBK")); 
   mp.addBodyPart(bp); 
   }
   
    //保存发送信息（mime）方式
   mimeMsg.setContent(mp); 
   mimeMsg.saveChanges(); 
   transport.sendMessage(mimeMsg,mimeMsg.getRecipients(Message.RecipientType.TO)); 
   transport.close(); 
       out.println("发送邮件成功！！！");
}
   catch(Exception e)    {
      out.println("发送邮件失败！！！");
      out.println(e.toString());     }
 

%>
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