How can I send notification to specific User using the user's token in Firebase?

Question

I am developing an android app (java), I am using Firebase, for each registered user I have a token of the device, how can I send a notification to a specific user using his token ?

Answer 1

For sending a notification to users the only thing required is that user's token. You can send notification using FCM. Here, I'm sharing my FCM class which can be used for this purpose. It is using Okhttp3 requests, so make sure you add its dependency.

    implementation 'com.squareup.okhttp3:okhttp:5.0.0-alpha.2'

After adding this dependency, all you have to do is to use this FCM class.

FCMMessages.java

public class FCMMessages {

    private Context context;

    public void sendMessageSingle(Context context, final String recipient, final String title, final String body, final Map<String, String> dataMap)
    {
        this.context = context;

        Map<String, Object> notificationMap = new HashMap<>();
        notificationMap.put("body", body);
        notificationMap.put("title", title);

        Map<String, Object> rootMap = new HashMap<>();
        rootMap.put("notification", notificationMap);
        rootMap.put("to", recipient);
        if (dataMap != null)
            rootMap.put("data", dataMap);

        new SendFCM().setFcm(rootMap).execute();
    }


    public void sendMessageMulti(Context context, final JSONArray recipients, final String title, final String body, final Map<String, String> dataMap) {
        this.context = context;

        Map<String, Object> notificationMap = new HashMap<>();
        notificationMap.put("body", body);
        notificationMap.put("title", title);
        Map<String, Object> rootMap = new HashMap<>();
        rootMap.put("notification", notificationMap);
        rootMap.put("registration_ids", recipients);
        if (dataMap != null)
            rootMap.put("data", dataMap);

        new SendFCM().setFcm(rootMap).execute();
    }

    @SuppressLint("StaticFieldLeak")
    class SendFCM extends AsyncTask<String, String, String> {

        private String FCM_MESSAGE_URL = "https://fcm.googleapis.com/fcm/send";
        private Map<String, Object> fcm;

        SendFCM setFcm(Map<String, Object> fcm) {
            this.fcm = fcm;
            return this;
        }

        @Override
        protected String doInBackground(String... strings) {
            try {
                MediaType JSON = MediaType.parse("application/json; charset=utf-8");
                RequestBody body = RequestBody.create(JSON, new JSONObject(fcm).toString());
                Request request = new Request.Builder()
                        .url(FCM_MESSAGE_URL)
                        .post(body)
                        .addHeader("Authorization","key=" + StaticConfig.myMessagingAuth)
                        .build();
                Response response = new OkHttpClient().newCall(request).execute();
                return response.body().string();

            } catch (Exception e) {
                e.printStackTrace();
                return null;
            }
        }

        @Override
        protected void onPostExecute(String result) {
            try {
                JSONObject resultJson = new JSONObject(result);
                int success, failure;
                success = resultJson.getInt("success");
                failure = resultJson.getInt("failure");
            //Toast.makeText(context, "Sent: " + success + "/" + (success + failure), Toast.LENGTH_LONG).show();
            } catch (JSONException e) {
                e.printStackTrace();
//                Toast.makeText(context, "Message Failed, Unknown error occurred.", Toast.LENGTH_LONG).show();
            }
        }
    }

}

Make sure you get the messagingAuth from your firebase project settings. To get the messagingAuth token, follow these steps:

Open Firebase Project > Project Settings > Cloud Messaging > Server key

Copy the value of server key and paste it as messagingAuth in your android project.

To send a notification to single user token use sendMessageSingle method. It would be like

String user_token = "wiubd92uhe91dik-q";
String notification_title = "This is notification title";
String notification_des = "This is notification description";
new FCMMessages().sendMessageSingle(MainActivity.this, user_token, notification_title, notification_des, null);

To send a notification to multiple user tokens use sendMessageMulti method. It would be like

ArrayList<String> user_tokens = new ArrayList<>();
user_tokens.add(token_1);
user_tokens.add(token_2);
user_tokens.add(token_3);
String notification_title = "This is notification title";
String notification_des = "This is notification description";
new FCMMessages().sendMessageMulti(MainActivity.this, new JSONArray(user_tokens), notification_title, notification_des, null);