SEND FIREBASE CLOUD MESSAGES (FCM) TO YOUR DESIRED ANDROID USERS USING NODE JS SERVER

Architecture:

As the figure says, we will send notification messages from our android set to our own server (say Node js web app). In the Node js web app we implemented the admin sdk of Firebase Cloud messaging (FCM) server. The Nodejs web app communicates with the firebase cloud server using its app credentials. The FCM (Firebase Cloud Messaging) server now serve the users of defined categories.

[This article should be read as the appended section of SEND YOUR FIRST ANDROID NOTIFICATION USING FCM (Firebase Cloud Messaging)]

 

1. In your Firebase console go to Project Settings>Service Accounts

2. In the Service Accounts window click Generate New Private Key. Then in the confirmation window click Generate Key.

3. The Google Credential json file will be downloaded to the downloads folder of the browser.

Keep this file safe.

4. We need to put this file in the project root of our Node js web app.

5. SETUP THE NODEJS WEB SERVER

Now install firebase admin sdk in our server.

In my case my server is an apache shared server. I have node js setup tool in it.

(i) first create a folder in my shared server root directory. Under it I will create my base directory for my nodejs web app.

(ii) it is better to create a demo app in our local WAMP or LAMP server with npm init.

(iii) the main app.js file along with package.json will be created there.

(iv) now upload this app.js along with package.json to our shared server base directory.

(v) Now go to nodejs setup.

(vi) specify Node js app root directory in Application root.

And put the application url.

(vii) Application startup file(app,js) & log file

(viii) click on Edit under Run NPM Install.

(ix) Here enter in the dependency section the firbase-admin as following:

“firebase-admin”: “”

(x) Now install packages by clicking Run NPM Install.

(xi) After successful installation open app.js and add the following code in app.js file:

var express = require('express')

var admin = require("firebase-admin");

const port = 2388;

app.get('/', (req,res)=>{

    res.status(200).send("Hello World")

})

app.listen(port, () =>{

console.log("listening to port"+port);

})

(xii) Save app.js and restart the web app from Node js setup.

 

(xiii) Setup the subdomain for your web app. Make https redirect to it. (xiv) Now in the browser test your web app by typing your (sub)domain name.

This will show now Hello World on the browser.

It proves that our web app setup is correct and working.

6. Now we have Google Credential json file containing firebase keys stored in the base directory of our web app.

7. Now inside the app.js add the following code to initialize the Firebase Admin SDK for messaging.

var admin = require("firebase-admin");

var serviceAccount = require("./myTopic-firebase-msg.json");

admin.initializeApp({

  credential: admin.credential.cert(serviceAccount),

  databaseURL: "htts://<your firebase database>.firebaseio.com"

})

Here myTopic-firebase-msg.json is the json file I downloaded in the step 3 and renamed it. I put this file in web app’s base directory.

Also the initialization requires a database url to the realtime database (rtdc) of your Firebase Account (You will get it from Real Time Database section on your Firebase console).

8. Further put a module like below to accept request from the messaging app that controls the notification to all users.

 app.post('/firebase/notification', (req, res)=>{

    var topic;

    var title;

    var message;

    var body = [];

    req.on('error', (error)=>{

        console.log(error);

    }).on('data', (chunk)=>{

        body.push(chunk);

   }).on('end', ()=>{

        body = Buffer.concat(body).toString();

        res.on('error', (err)=>{                                   

                console.error('Error Occured :'+err);

        });

        var json = JSON.parse(body);

        topic = json.topic

        title = json.title

        message = json.body

   

        const messaging = admin.messaging();

        var payload = {

                notification: {

                        title: title,

                        body: message

                }

        };

        messaging.sendToTopic(topic, payload)

        .then(result=>{

                Console.log('The response: '+result)

        });

        res.send('Its OK..');

        res.end();

   })

})

Here be careful to construct the right payload with notification and topic. This payload will reach to the end users.

9. Now save the app.js file. Restart the Node js web app from nodejs setup.

10. Now make the following changes in our message sending android app:

In your MainActivity do the following changes:

   

public class MainActivity extends AppCompatActivity{

        protected void onCreate(Bundle savedInstanceState) {

                super.onCreate(savedInstanceState);

                setContentView(R.layout.your_layout);

               

                --------   --------- ------

                Button btn = findViewById(R.id.sendMsg);

                Btn.setOnClickListener(new View.OnClickListener() {

                @Override

                public void onClick(View v) {

                        AsyncTaskClass asyncClass = new AsyncTaskClass();

                        asyncClass.execute();

                 }

                });

        }

 

        class AsyncTaskClass extends AsyncTask<Void,Void,String> {

        @Override

        protected void onPreExecute() {

            super.onPreExecute();

        }

 

        @Override

        protected void onPostExecute(String string1) {

            super.onPostExecute(string1);

        }

 

        @Override

        protected String doInBackground(Void... params) {

            ServerUploadPath = "https://your.domain.com/firebase/notification";

            String topic = "urgent";

                        String title = "Test Notification";

                        String body = "Meeting called at 8:30 pm";

            QString = makeMessageString(new MsgToSend(topic , title, body));

 

            String finalData = sendData(ServerUploadPath,QString);

            runOnUiThread(new Runnable() {

                @Override

                public void run() {

                    //process the response finalData

                }

            });

            return finalData;

        }

    }

       

        private String sendData(String requestURL, String QString){

                final StringBuilder stringBuilder = new StringBuilder();

 

        try {

 

            URL url;

            HttpURLConnection httpURLConnectionObject ;

            OutputStream outPutStream;

            BufferedWriter bufferedWriterObject ;

            BufferedReader bufferedReaderObject ;

            int respCode ;

 

            url = new URL(requestURL);

 

            httpURLConnectionObject = (HttpURLConnection) url.openConnection();

            httpURLConnectionObject.setReadTimeout(19000);

            httpURLConnectionObject.setConnectTimeout(19000);

            httpURLConnectionObject.setRequestMethod("POST");

            httpURLConnectionObject.setDoInput(true);

            httpURLConnectionObject.setDoOutput(true);

            outPutStream = httpURLConnectionObject.getOutputStream();

            bufferedWriterObject = new BufferedWriter(new OutputStreamWriter(outPutStream, "UTF-8"));

            bufferedWriterObject.write(QString);

            bufferedWriterObject.flush();

            bufferedWriterObject.close();

            outPutStream.close();

            respCode = httpURLConnectionObject.getResponseCode();

            if (respCode == HttpsURLConnection.HTTP_OK) {

                bufferedReaderObject = new BufferedReader(new InputStreamReader(httpURLConnectionObject.getInputStream()));

                //StringBuilder stringBuilder1 = new StringBuilder();

                String received;

                while ((received = bufferedReaderObject.readLine()) != null){

                    stringBuilder.append(received);

                }

                                Handler handler = new Handler(Looper.getMainLooper());

                handler.post(new Runnable() {

                    @Override

                    public void run() {

                        Toast.makeText(MainActivity.this, stringBuilder.toString(), Toast.LENGTH_LONG).show();

                    }

                });

            }

 

        } catch (Exception e) {

            e.printStackTrace();

        }

        return stringBuilder.toString();

       

        }

       

        private class MsgToSend{

        String topic;

        String title;

        String body;

        public MsgToSend(String topic,String title, String body){

            this.topic = topic;

            this.title = title;

            this.body = body;

        }

    }

        private String makeMessageString(MsgToSend msg){

        Gson gson = new Gson();

        Type type = new TypeToken<MsgToSend>(){}.getType();

        String rjson = gson.toJson(msg,type);

        return rjson;

    }

}      

 

11. In the user’s client Android app keep the FrebaseMessageReceiver class unchanged. (This class we created earlier in the previous section -SEND YOUR FIRST ANDROID NOTIFICATION USING FCM).

Also, In the main launcher activity onCreate method must add the following code to subscribe the user for definite topic.

FirebaseMessaging.getInstance().subscribeToTopic(topicname);

To unsubscribe the topic topicname user app must call unsubscribeFromTopic(topicname);

FirebaseMessaging.getInstance().unsubscribeFromTopic(topicname);

Note:

12. This change in user’s client android app will enable it to receive FCM messages based on its subscribed topic.

Now Install client android app in user’s device and install the sender app to your device. On clicking the button on sender app push notification will be served to those user’s app who have subscribed to topic “urgent” (as I have mentioned “urgent” as the topic in query string (QString) in my sender’s app. This query string is collected by our nodejs web app and extracts the topic from this query.).

 

FURTHER READING: HANDLING RECEIVING OF FCM MESSAGES IN ANDROID IN EFFICIENT MANNER.