I want to download a file from the frontend, need to send input stream to the frontend. Using download link to download file from backend

Question

The code below uses a protected url ,username password to get the files to download. I can only manage to download the file in the springboot folder. I want to send the file data to the frontend to have it download there to your downloads.

I might be wrong but I need to send the inputstream to the frontend, then download that data to a file? Any suggestions as to what I am doing wrong when trying to send this data to the frontend.

@RequestMapping(value = "/checkIfProtectedOrPublic/", method = RequestMethod.POST)
        public ResponseEntity checkIfProtectedOrPublic(@RequestPart("prm_main") @Valid CheckProtectedData checkProtectedData) throws IOException {
    
            List<PrmMain> prmMainList = prmMainRepository.findAllByCode("PROTECTED_LOGIN");
            boolean success = true;
            InputStream in = null;
            FileOutputStream out = null;
    
    
            for (int i = 0; i < prmMainList.size(); i++) {
                if (prmMainList.get(i).getData().get("email").equals(checkProtectedData.getEmail())) {
    
    String username= (String) prmMainList.get(i).getData().get("email");
    String password= (String) prmMainList.get(i).getData().get("password");
    
    
    
                    try{
                        URL myUrl = new URL(checkProtectedData.getDownloadLink());
                        HttpURLConnection conn = (HttpURLConnection) myUrl.openConnection();
                        conn.setDoOutput(true);
                        conn.setReadTimeout(30000);
                        conn.setConnectTimeout(30000);
                        conn.setUseCaches(false);
                        conn.setAllowUserInteraction(false);
                        conn.setRequestProperty("Content-Type", "application/json");
                        conn.setRequestProperty("Accept-Charset", "UTF-8");
                        conn.setRequestMethod("GET");
    
                        String userCredentials = username.trim() + ":" + password.trim();
                        String basicAuth = "Basic " + new String(Base64.encode(userCredentials.getBytes()));
                        conn.setRequestProperty ("Authorization", basicAuth);
    
                        in = conn.getInputStream();
    
    
                        out = new FileOutputStream(checkProtectedData.getFileName());
                        int c;
                        byte[] b = new byte[1024];
    
                        while ((c = in.read(b)) != -1){
                            out.write(b, 0, c);
                        }
                    }
    
                    catch (Exception ex) {
    
                        success = false;
                    }
    
                    finally {
                        if (in != null)
                            try {
                                in.close();
                            } catch (IOException e) {
    
                            }
                        if (out != null)
                            try {
                                out.close();
                            } catch (IOException e) {
    
                            }
                    }
                }
            }
    
    
    
            return ResponseEntity.of(null);
    
        }