利用jsp下载excel时出现乱码~！懂的来

jsp页面如下：
<%@ page contentType="text/html; charset=GBK"%>
<%@ include file = "/common/common.inc"%><%@ 
page import="java.io.*" %><%@ 
taglib uri="/WEB-INF/supp_struts.tld" prefix="supp" %><%@ 
include file = "/common/javascript.inc"%><%@
page import="com.supporter.prj.com_codetable.*"%><%@ 
page import="com.supporter.util.*" %><%@ 
page import="com.supporter.prj.file_upload.*" %>
<% 
//接收参数
    String fileName = request.getParameter("fileName");
    if (CommonUtil.trim(fileName).length() <= 0) {
        System.out.println("file_downlod.jsp: invalid fileId :" + fileName);
        out.println("无效的文件标识：" + fileName);
        return;
    }
String ls_FilePath = pageContext.getServletContext().getRealPath("/").replace('\\','/') + "/bm/item/" + fileName;
FileInputStream lfis_Source = null;
OutputStream los_OutputStream = null;
try{
//        response.setContentType("application/ms-excel");
        response.setContentType("application/vnd.ms-excel");
        response.setHeader("Content-Disposition;charset=GBK", "attachment; filename=bbb" + CommonUtil.unicodeToGB(fileName));
        response.setBufferSize(1024); 
        
File lfile_F = new File(ls_FilePath);
lfis_Source = new FileInputStream(lfile_F);
los_OutputStream = response.getOutputStream();
       byte[] larrbyte_Buffer = new byte[1024];
    int li_Bytes = 0;
    while((li_Bytes = lfis_Source.read(larrbyte_Buffer)) != -1){
        los_OutputStream.write(larrbyte_Buffer,0,li_Bytes);
    } 
           
    } catch (IOException e){
       e.printStackTrace(); 
    } finally {
     if(lfis_Source != null){
     lfis_Source.close();
     }
       if(los_OutputStream != null){
       los_OutputStream.close();  
       }
    }%>
xml配置了：
<mime-mapping> 
<extension>xls</extension> 
<mime-type>application/msexcel</mime-type>
</mime-mapping>拜托各位高手帮解决一下，下载下来的文件乱码 （我用tomcat环境跑起来就不乱码，用weblogic跑起来就乱码）急~！！！！！！！！！！！！！！！！！！！！！！！