java downloads a file through url and outputs it

Examples are as follows:

controller : 
@RequestMapping(value = "/{loanid}/{atmtType}")
 public void doGet(@PathVariable("loanid") String loanid,@PathVariable("atmtType") String atmtType,
   HttpServletRequest req,HttpServletResponse response) {
  Map<String,String> map = new HashMap<String,String>();
  map.put("loanid", loanid);
  Map<String, String> urlByLoanid= new HashMap<String,String>();
 // Map<String, String> urlByLoanid = zcmQueryInfoService.queryUrlByLoanid(map);
  try {
   if(urlByLoanid!=null){
    String wjurl="http://10.0.15.11:8080/gateway//nfs/marvel-core-admin/2017/10/11/compact_seal_17101119371231615_7.pdf";
    //String wjurl = urlByLoanid.get("url");
    int i = wjurl.lastIndexOf("/");
    String fileName = wjurl.substring(i+1);
    
    URL url = new URL(wjurl); 
    HttpURLConnection conn = (HttpURLConnection)url.openConnection(); 
    // Set the timeout to 3 seconds  
    conn.setConnectTimeout(3*1000); 
    // Prevents the masking program from fetching and returning 403 error  
    conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)"); 
    // Get the input stream  
    InputStream inputStream = conn.getInputStream(); 
    // Get your own array  
    byte[] bs = readInputStream(inputStream); 
    response.setContentType("application/octet-stream;charset=ISO8859-1");
    BufferedOutputStream output = null;
    BufferedInputStream input = null;
     try {
      output = new BufferedOutputStream(response.getOutputStream());
      //  Chinese file name must be transcoded as  ISO8859-1, Otherwise it's a mess 
      String fileNameDown = new String(fileName.getBytes(), "ISO8859-1");
      //  Download as an attachment 
      response.setHeader("Content-Disposition", "attachment;filename=" + fileNameDown);
  
      output.write(bs);
      response.flushBuffer();
     } catch (Exception e) {
      log.error("Download log file error", e);
     } //  The user may have cancelled the download 
     finally {
      if (input != null)
       try {
        input.close();
       } catch (IOException e) {
        e.printStackTrace();
       }
      if (output != null)
       try {
        output.close();
       } catch (IOException e) {
        e.printStackTrace();
       }
     }
   }
  } catch (Exception e) {
   e.printStackTrace();
  }
 }
/** 
  *  Gets the byte array from the input stream  
  * @param inputStream 
  * @return 
  * @throws IOException 
  */ 
 public static byte[] readInputStream(InputStream inputStream) throws IOException { 
  byte[] buffer = new byte[1024]; 
  int len = 0; 
  ByteArrayOutputStream bos = new ByteArrayOutputStream(); 
  while((len = inputStream.read(buffer)) != -1) { 
   bos.write(buffer, 0, len); 
  } 
  bos.close(); 
  return bos.toByteArray(); 
 }