unable to send byte array to controller

Question

I am trying to send file byte from client to controller through base64 encoded string. I am able to send normal string of less size . but when I try to send long String(base 64 binary encoded) , getting null at server side. Kindly guide me. my Server side and client side code are below

At Client side

try{
        byte[] getBytes = Files.readAllBytes(Paths.get("C:/Sample/123.csv"));

        byte[] enc = Base64.encodeBase64(getBytes);  
        String encodedString = new String(enc);
 String urlParameters  = "param1="+encodedString+"&param2=virendra";
 byte[] postData       = urlParameters.getBytes( StandardCharsets.UTF_8 );
        int    postDataLength = postData.length;
        System.out.println(postDataLength);
        String request        = "http://localhost:9090//getSingerDetails";
        URL    url            = new URL( request );
        HttpURLConnection conn= (HttpURLConnection) url.openConnection();           
        conn.setDoOutput( true );
        conn.setInstanceFollowRedirects( false );
        conn.setRequestMethod( "POST" );
        conn.setRequestProperty( "Content-Type", "application/x-www-form-urlencoded"); 
        conn.setRequestProperty( "charset", "utf-8");
        conn.setRequestProperty( "Content-Length", Integer.toString( postDataLength ));
        conn.setUseCaches( false );
        try( DataOutputStream wr = new DataOutputStream( conn.getOutputStream())) {
           wr.write( postData );
        }
        System.out.println("Response Code FOR bulkDataUpload : "+conn.getResponseCode());
    }
            catch(Exception e){
                e.printStackTrace();

            }

AT server side code

@RequestMapping(value = "/getSingerDetails", method = RequestMethod.POST)
        public @ResponseBody JsonResponse seeding2BackendTrans (Map<String, String> map, HttpSession session,   
                @RequestParam Map<String,Object> param ) throws IOException {

            System.out.println("param1-->"+String.valueOf(param.get("param1")));
            System.out.println("param2-->"+String.valueOf(param.get("param2")));

I am getting value of param1 and param2 is null. but when I pass statice value encodedString . I am getting correct out put. Please help.

Thanks