public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        File filename = new File("D:\\chengxu\\ML\\2.excel");
  

       //設定檔案ContentType型別，這樣設定，會自動判斷下載檔案型別  
response.setContentType("multipart/form-data");
//設定編碼格式
        response.setCharacterEncoding("UTF-8");  
        //設定可以識別Html檔案  
        response.setContentType("text/html");
        // 2.設定檔案頭：最後一個引數是設定下載檔名  

        response.setHeader("Content-Disposition", "attachment;filename="+filename.getName());

//（這裡  可以設定成excel格式 ：response.setHeader("Content-Disposition", "attachment;fileName=" + “檔名” + ".xsl");
        //可以設定成.pdf格式 ：response.setHeader("Content-Disposition", "attachment;fileName=" + “檔名” + ".pdf");

       OutputStream out = response.getOutputStream();

        
        FileInputStream fileinput = new FileInputStream(filename);
        
       try {
       out = response.getOutputStream();  
       int b = 0;  
       byte[] buffer = new byte[1024];  
       while ((b = fileinput.read(buffer)) != -1) {  
           // 4.寫到輸出流(out)中  
           out.write(buffer, 0, b);  
       }  
} catch (Exception  e) {
e.printStackTrace();
}finally{
fileinput.close();  
    out.flush();  
    out.close();  
}
        
    }