sending push notification from java

push_notification.java

import com.google.api.client.googleapis.auth.oauth2.GoogleCredential;
import com.google.auth.oauth2.GoogleCredentials;
import com.google.firebase.FirebaseApp;
import com.google.firebase.FirebaseOptions;
import com.google.firebase.messaging.FirebaseMessaging;
import com.google.firebase.messaging.FirebaseMessagingException;
import com.google.firebase.messaging.Message;
import com.google.firebase.messaging.Notification;
import org.junit.Before;
import org.junit.Test;

import java.io.FileInputStream;
import java.io.IOException;
import java.util.Arrays;

public class NotificationService {

    @Before
    public void init() throws IOException {

    }
    @Test
    public void sendPushTest() throws IOException, FirebaseMessagingException {

        initFirebaseApp();

        String accessToken = getAccessToken();
        //@abdullah please be sure token is up to date 
        String registrationToken = "your token for test";


        Notification notification =  Notification.builder()
                .setTitle("from Server")
                .setBody("Message Body")
                .build();

        Message message = Message.builder()
                .putData("dataType", "DataValue")
                .putData("DataType2", "DataValue2")
                .setToken(registrationToken)
                .setNotification(notification)
                .build();

        String response = FirebaseMessaging.getInstance().send(message);

        System.out.println("Successfully sent message: " + response);

    }

    void initFirebaseApp() throws IOException{

        FileInputStream serviceAccount =
                new FileInputStream("service/service_account.json");

        FirebaseOptions options = new FirebaseOptions.Builder()
                .setCredentials(GoogleCredentials.fromStream(serviceAccount))
                .setDatabaseUrl("https://veemu-33e81.firebaseio.com")
                .build();

        FirebaseApp.initializeApp(options);

    }

    private static String getAccessToken() throws IOException {
        GoogleCredential googleCredential = GoogleCredential
                .fromStream(new FileInputStream("service/service_account.json"))
                .createScoped(Arrays.asList(
                        "https://www.googleapis.com/auth/admin.directory.notifications",
                        "https://www.googleapis.com/auth/firebase.messaging"
                ));
        googleCredential.refreshToken();
        return googleCredential.getAccessToken();
    }




}