FirebasePushNotificationTopics

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.tabian.firebasepushnotifications.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        android:id="@+id/textView"/>



</RelativeLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          package="com.tabian.firebasepushnotifications">

    <uses-permission android:name="android.permission.INTERNET"></uses-permission>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>

                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>

        <service
            android:name=".FirebaseMessagingService">
            <intent-filter>
                <action android:name="com.google.firebase.MESSAGING_EVENT"/>
            </intent-filter>
        </service>

        <meta-data
            android:name="com.google.firebase.messaging.default_notification_color"
            android:resource="@color/colorAccent" />
    </application>

</manifest>

firebase_send_postman_topics.txt

{
  "to": 
    "/topics/NEWYORK_WEATHER"
  ,
  "data": {
    "extra_information": "This is some extra information"
  },
  "notification": {
    "title": "New York Weather Update!",
    "text": "This is the notification message.",
  }
}

FirebaseMessagingService.java

package com.tabian.firebasepushnotifications;

import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.media.RingtoneManager;
import android.net.Uri;
import android.support.v4.app.NotificationCompat;
import android.util.Log;

import com.google.firebase.messaging.RemoteMessage;

import org.json.JSONException;
import org.json.JSONObject;


public class FirebaseMessagingService extends com.google.firebase.messaging.FirebaseMessagingService  {
    private static final String TAG = "FirebaseMessagingServic";

    public FirebaseMessagingService() {
    }

    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        // Check if message contains a data payload.
        if (remoteMessage.getData().size() > 0) {
            Log.d(TAG, "Message data payload: " + remoteMessage.getData());

        }

        // Check if message contains a notification payload.
        if (remoteMessage.getNotification() != null) {
            String title = remoteMessage.getNotification().getTitle(); //get title
            String message = remoteMessage.getNotification().getBody(); //get message

            Log.d(TAG, "Message Notification Title: " + title);
            Log.d(TAG, "Message Notification Body: " + message);

            sendNotification(title, message);
        }
    }

    @Override
    public void onDeletedMessages() {

    }

    private void sendNotification(String title,String messageBody) {
        Intent intent = new Intent(this, MainActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0 /* Request code */, intent,
                PendingIntent.FLAG_ONE_SHOT);

        Uri defaultSoundUri= RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
        NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
                .setSmallIcon(R.mipmap.ic_launcher)
                .setContentTitle(title)
                .setContentText(messageBody)
                .setAutoCancel(true)
                .setSound(defaultSoundUri)
                .setContentIntent(pendingIntent);

        NotificationManager notificationManager =
                (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

        notificationManager.notify(0 /* ID of notification */, notificationBuilder.build());
    }
}

MainActivity.java

package com.tabian.firebasepushnotifications;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import com.google.firebase.messaging.FirebaseMessaging;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        FirebaseMessaging.getInstance().subscribeToTopic("NEWYORK_WEATHER");
        //FirebaseMessaging.getInstance().unsubscribeFromTopic("NEWYORK_WEATHER");
    }
}