java servlet文件下载 结果直接打开了？？？

response.setCharacterEncoding("GBK");   
        ServletOutputStream out1 = response.getOutputStream();   
        int act =4; //Integer.parseInt(request.getParameter("act"));   
        String filename="";   
        if(act==1)filename="1.rar";   
        else if(act==2)filename="2.rar";   
        else if(act==3)filename="3.rar";   
        else filename="c.rar";   
           
  
        File file2 = new File("d:\\"+filename);   
        if (!file2.exists()) {   
            response.setContentType("application/x-download");   
            out1.print("file doesn't exist");   
            return;   
        }else {   
            response.setHeader("Content-Disposition",   
                    "attachment; filename=default\"" + "\"");   
          //  filename=filename.substring(filename.lastIndexOf("\\"));   
            response.setHeader("Content-Disposition", "attachment; filename=\""  
                    + filename + "\"");   
        }   
  
        BufferedInputStream bis = null;   
        BufferedOutputStream bos = null;   
        try {   
            bis = new BufferedInputStream(new FileInputStream(file2));   
            bos = new BufferedOutputStream(out1);   
            byte[] buff = new byte[2048];   
            int bytesRead;   
            while (-1 != (bytesRead = bis.read(buff, 0, buff.length))) {   
                bos.write(buff, 0, bytesRead);   
            }   
        } catch (IOException e) {   
            throw e;   
        } finally {   
            if (bis != null)   
                bis.close();   
            if (bos != null)   
                bos.close();   
        }  
为什么会直接打开呢？有什么办法能让它弹出下载呢？