Record a Phone Message with Java

Introduction

In a previous tutorial, we showed you how to Receive a Phone Call with Java and respond using text to speech. We can also allow users to leave a message and then retrieve that recorded message.

Prerequisites

To work through this tutorial, you will need a Nexmo account. Sign up now if you don't already have an account.

You will be using Gradle to manage your dependencies and run your application. Additionally, you'll need to make sure you have a copy of the JDK installed. I will be using JDK 8 in this tutorial.

Finally, you'll need the Nexmo CLI installed. You'll use it to purchase a phone number and configure your Nexmo account to point at your new application.

Record a Phone Message with Java

This tutorial will walk you through the following steps:

1. Using Gradle to setup a new Java project.
2. Using the Spark framework for controlling the call.
3. Purchasing a number and configuring your Nexmo account to use that number with your application.

Using Gradle to Setup a New Java Project

You will use Gradle to manage your dependencies and to create and run your Java application.

The gradle init --type=java-application command will create all of the folders you will need as well as a sample class where you will be writing your code.

From the command line, create a new Java project with the following commands:

mkdir record-a-message
cd record-a-message
gradle init --type=java-application

Using the Spark Framework for Controlling the Call

You will use the Spark framework to receive a HTTP call made by Nexmo when your number receives a call, and to receive the request that Nexmo sends after the message has been recorded.

Adding the Dependencies

Add the following to the dependencies block in your build.gradle file:

// Spark Framework
compile 'com.sparkjava:spark-core:2.7.2'

// Nexmo Java Client
compile 'com.nexmo:client:4.0.1'

Your dependencies block should look like this:

dependencies {
    compile 'com.sparkjava:spark-core:2.7.2'
    compile 'com.nexmo:client:4.0.1'

    // Use JUnit test framework
    testCompile 'junit:junit:4.12'
}

Gradle will create the App class in the src/main/java folder. Inside of this class is a getGreeting and a main method. You won't need the getGreeting method, so feel free to remove it.

Define the Answer Route

First, you will define the route that will be used for answering the call. When a call is received, Nexmo will send a request to a pre-defined webhook URL. It expects to receive a Nexmo Call Control Object (NCCO) containing a list of actions to execute.

When the phone call is answered, your application will instruct Nexmo to execute three actions:

1. A talk action to greet the caller and instruct them on how to leave a message.
2. A record action which will instruct the Voice API to start recording.
3. A talk action to thank them for leaving a message.

This is the resulting NCCO that your application will create:

[
  {
    "text": "Please leave a message after the tone, then press #. We will get back to you as soon as we can.",
    "action": "talk"
  },
  {
    "endOnSilence": 3,
    "endOnKey": "#",
    "beepStart": true,
    "eventUrl": [
      "http://your-web-address/webhooks/recordings"
    ],
    "action": "record"
  },
  {
    "text": "Thank you for your message. Goodbye",
    "action": "talk"
  }
]

Add the following to the main method of the App class, making sure to resolve all imports:

/*
* Route to answer and connect incoming calls with recording.
*/
Route answerRoute = (req, res) -> {
    String recordingUrl = String.format("%s://%s/webhooks/recordings", req.scheme(), req.host());

    TalkAction intro = new TalkAction.Builder("Please leave a message after the tone, then press #. We will get back to you as soon as we can.")
            .build();

    RecordAction record = new RecordAction.Builder()
            .eventUrl(recordingUrl)
            .endOnSilence(3)
            .endOnKey('#')
            .beepStart(true)
            .build();

    TalkAction outro = new TalkAction.Builder("Thank you for your message. Goodbye").build();

    res.type("application/json");

    return new Ncco(intro, record, outro).toJson();
};

The record action has a few different properties. For example, you can define the event url that will be sent a request when the recording is finished, end the recording on a specific key press, and play a beep at the start of the recording.

Define the Recordings Route

The record action has a property called eventUrl which is used to communicate when the recording is finished. The following is an example of the return parameters sent to the event url:

{
  "start_time": "2020-01-01T12:00:00Z",
  "recording_url": "https://api.nexmo.com/media/download?id=aaaaaaaa-bbbb-cccc-dddd-0123456789ab",
  "size": 12345,
  "recording_uuid": "aaaaaaaa-bbbb-cccc-dddd-0123456789ab",
  "end_time": "2020-01-01T12:01:00Z",
  "conversation_uuid": "bbbbbbbb-cccc-dddd-eeee-0123456789ab",
  "timestamp": "2020-01-01T14:00:00.000Z"
}

The Nexmo Java Client has a class called RecordEvent which can be used to deserialize the JSON sent to eventUrl. For now, you're going to output the recording_url to the console.

Add the following to the main method of the App class, resolving any imports:

/*
* Route which prints out the recording URL it is given to stdout.
*/
Route recordingRoute = (req, res) -> {
    RecordEvent recordEvent = RecordEvent.fromJson(req.body());
    System.out.println(recordEvent.getUrl());

    res.status(204);
    return "";
};

Register the Routes

Up until this point you have defined two routes:

• The first route will respond to Nexmo with an NCCO when Nexmo answers the incoming call.
• The second route will log the recording URL when Nexmo finishes recording the message.

In order to use these routes, we need to configure Spark. Your application will listen on port 3000, and the routes will be configured on /webhooks/answer and /webhooks/recordings.

Add the following to the main method of the App class:

Spark.port(3000);
Spark.get("/webhooks/answer", answerRoute);
Spark.post("/webhooks/recordings", recordingRoute);

Purchasing a Number

You will need a Nexmo number in order to receive phone calls. If you do not have a number you can use the Nexmo CLI to purchase one:

nexmo number:buy --country_code US

Take note of the number that is assigned to you on purchase. You will need this number to link your application and for testing.

Exposing Your Application

In order to send an HTTP request to your application, Nexmo needs to know the URL that your application is running on.

Instead of configuring your local network or hosting your application on an external service, you can use ngrok to safely expose your application to the internet.

Download ngrok and run the following command:

ngrok http 3000

Take note of the forwarding address as you will need it when you configure your account. In the following picture, the forwarding address is http://99cad2de.ngrok.io.

Configure Your Nexmo Account

If you do not have an application you can use the Nexmo CLI to create one using your ngrok forwarding address:

nexmo app:create "Record Message Demo" http://your-ngrok-forwarding-address/webhooks/answer http://your-ngrok-forwarding-address/webhooks/events --keyfile private.key

After running this command, you will be shown an an application id. For example: notreal-1111-2222-3333-appid. You will need this application id to link your phone number to the application.

You can use the Nexmo CLI to link your phone number and application:

nexmo link:app your-nexmo-phone-number your-application-id

This command instructs Nexmo to create a new application on your account. The application will send a request to the first URL when it receives a phone call. The application will send requests to the second URL when the call status changes.

Test Your Application

Start your application with the gradle run command inside of your record-a-message directory.

Make a call to your Nexmo number and test out your application. You will hear the message, "Please leave a message after the tone, then press #. We will get back to you as soon as we can." Once you hear the beep, leave a message and then press #. You should then hear "Thank you for your message. Goodbye." and the recording URL will be displayed on your console.

Conclusion

In a few lines of code you have created an application that can receive a phone call, record a message, and then display the URL to that recording.

Check out our documentation on Nexmo Developer where you can learn more about call flow or Nexmo Call Control Objects. See our Nexmo Quickstart Examples for Java for full code examples on this tutorial and more.

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