Firebase Cloud Messaging (FCM) with Java

Some time ago I needed a simple way to send Push Messages with Firebase Cloud Messaging (FCM), so I wrote FcmJava:

FcmJava implements the entire Firebase Cloud Messaging HTTP Protocol and supports:

  • Downstream HTTP Messages
  • Notification Payloads
  • Topic Messages
  • Device Group Messages

Firebase Cloud Messaging (FCM) is basically the successor to Google Cloud Messaging, so it was easy to port my .NET library to Java.

Maven Dependencies

You can add the following dependencies to your pom.xml to include FcmJava in your project.

<dependency>
  <groupId>de.bytefish.fcmjava</groupId>
  <artifactId>fcmjava-core</artifactId>
  <version>0.6</version>
</dependency>

<dependency>
  <groupId>de.bytefish.fcmjava</groupId>
  <artifactId>fcmjava-client</artifactId>
  <version>0.6</version>
</dependency>

Quickstart

The Quickstart shows you how to work with FcmJava and with Firebase Cloud Messaging for an Android application.

The Android application is taken from Googles GitHub repository for the Firebase Quickstart with Android:

The example server application uses FcmJava to send a Push data message to the news Topic. I have implemented the FileContentBasedSettings class to read the API token from a file.

FcmClient

// Copyright (c) Philipp Wagner. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.

package de.bytefish.fcmjava.integration;

import com.fasterxml.jackson.annotation.JsonProperty;
import de.bytefish.fcmjava.client.FcmClient;
import de.bytefish.fcmjava.constants.Constants;
import de.bytefish.fcmjava.http.options.IFcmClientSettings;
import de.bytefish.fcmjava.model.options.FcmMessageOptions;
import de.bytefish.fcmjava.model.topics.Topic;
import de.bytefish.fcmjava.requests.topic.TopicUnicastMessage;
import org.junit.Ignore;
import org.junit.Test;

import java.nio.charset.Charset;
import java.time.Duration;

public class FcmClientIntegrationTest {

    private class PersonData {

        private final String firstName;
        private final String lastName;

        public PersonData(String firstName, String lastName) {
            this.firstName = firstName;
            this.lastName = lastName;
        }

        @JsonProperty("firstName")
        public String getFirstName() {
            return firstName;
        }

        @JsonProperty("lastName")
        public String getLastName() {
            return lastName;
        }
    }

    @Test
    @Ignore("This is an Integration Test using system properties to contact the FCM Server")
    public void SendTopicMessageTest() throws Exception {

        // Creates the Client using the default settings location, which is System.getProperty("user.home") + "/.fcmjava/fcmjava.properties":
        FcmClient client = new FcmClient();

        // Message Options:
        FcmMessageOptions options = FcmMessageOptions.builder()
                .setTimeToLive(Duration.ofHours(1))
                .build();

        // Send a Message:
        client.send(new TopicUnicastMessage(options, new Topic("news"), new PersonData("Philipp", "Wagner")));
    }
}

API Key

By default the FCM API Key is read from an external .properties file called fcmjava.properties to ensure the API Key secret does not reside in code or leaks into the public. The default location of the fcmjava.properties is System.getProperty("user.home") + "/.fcmjava/fcmjava.properties".

The file has to contain the FCM API Endpoint and the API Key:

fcm.api.url=https://fcm.googleapis.com/fcm/send
fcm.api.key=<YOUR_API_KEY_HERE>

If the properties are available in the default location you can simply instantiate the FcmClientas seen in the example.

You can use the PropertiesBasedSettings class to read the Properties and pass them into the FcmClient, if the Properties path differs from the default path:

  1. PropertiesBasedSettings.createFromDefault()
    • Uses the default file location of System.getProperty("user.home") + "/.fcmjava/fcmjava.properties" to read the properties. This is the recommended way of reading your API Key.
  2. PropertiesBasedSettings.createFromFile(Path path, Charset charset)
    • Uses a custom file location to read the settings from.
  3. PropertiesBasedSettings.createFromSystemProperties()
    • Uses the System Properties to initialize the settings.

Android Client

I have decided to clone the messaging quickstart sample of Google, which is available at:

Now first subscribe to the news topic, then execute the above FcmJava application.

The Android app will now receive a message with the sent data included:

09-17 21:10:45.250 10882-11300/com.google.firebase.quickstart.fcm D/MyFirebaseMsgService: From: /topics/news
09-17 21:10:45.251 10882-11300/com.google.firebase.quickstart.fcm D/MyFirebaseMsgService: Message data payload: {lastName=Wagner, firstName=Philipp}

Additional Resources

I have written an example Weather Warning Application using FcmJava.

The Android Application can be found at:

The server-side using FcmJava can be found at:

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