User details API call for checking if user exist or not.

gistfile1.java

NOTE: Call this below API in ASYNC task or any other as this is server call.   
              
CODE :
            UserClientService userClientService = new UserClientService(MainActivity.this);
            Set<String> userIds = new HashSet<>();
            userIds.add("<RECIVER-USER-ID>"); // PASS the userID :
            String response = userClientService.getUserDetails(userIds);
            Log.i("USER", "The Response is :" + response);

            if (TextUtils.isEmpty(response) || !TextUtils.isEmpty(response) && response.equals("error")) {
                // Failed to fetch the details due some net issue or connecting issue
            } else if (!TextUtils.isEmpty(response) && response.equals("[]")) {
                // User is not register call the register API and wait for login API call success and launch the chat after that..
                Log.i("USER", "NOT registered in applozic :" + response);
            } else {
                // User is already register launch the chat that user.
                Log.i("USER", "registered user already:" + response);
            }