//This functions call when user click on print declaration form button 
public void openPDF(HttpServletRequest req,HttpServletResponse res){
 try {
      ServletContext context = req.getServletContext();
      String contextpath = context.getRealPath("/")+GlobalVariables.OUTPUT_FOLDER;
      HttpSession session = req.getSession();   
      String user_order_id ="";
      if(session.getAttribute("user_order_id") != null){
         user_order_id = session.getAttribute("user_order_id").toString(); //when user_order_id already exists in session .
       }
      String fileName = user_order_id+"-PrintLabels.pdf";
      res.setContentType("application/pdf");
      res.setHeader("Expires", "0");
      res.setHeader("Cache-Control","must-revalidate, post-check=0, pre-check=0");
      res.setHeader("Content-Disposition","inline;filename=" + fileName);
      res.setHeader("Accept-Ranges", "bytes");
      File nfsPDF = new File(contextpath+ fileName);
      FileInputStream fis = new FileInputStream(nfsPDF);
      BufferedInputStream bis = new BufferedInputStream(fis);
      ServletOutputStream sos = res.getOutputStream();
      byte[] buffer = new byte[2048];
      while (true) {
        int bytesRead = bis.read(buffer, 0, buffer.length);
        if (bytesRead < 0) {
          break;
        }
      sos.write(buffer, 0, bytesRead);
      sos.flush();
      }
      sos.flush();
      bis.close();
    } catch (Exception e) {
      e.printStackTrace();
    }
}