# How to call Functions from Android

Twilio Functions are a perfect fit for mobile app developers. You can focus on writing your app, and let Twilio host and run the server code you need.

You don't need a special Twilio SDK or library to call Twilio Functions from your mobile app—your Function will respond to a normal HTTP call. We'll use Google's [Volley](https://developer.android.com/training/volley/index.html) HTTP Networking library with this example, but you can use other HTTP libraries for Java or Android if you would like.

In this guide, we'll show you how to set up a Twilio Function, call it from a web browser, and then call that function from an Android application. Our function will return a joke as a string. You could extend it to make it choose a random joke from a list, or by category. We'll keep it brief, and just return a hard coded string.

Let's start by creating a Function and giving it the path of `/joke`. Be sure to set the visibility of this Function to **public**, to avoid any hurdles when making your HTTP calls:

## Create and host a Function

Before you run any of the examples on this page, create a Function and paste the example code into it. You can create a Function in the Twilio Console or by using the [Serverless Toolkit](/docs/labs/serverless-toolkit).

## Console

If you prefer a UI-driven approach, complete these steps in the Twilio Console:

1. Log in to the [Twilio Console](https://1console.twilio.com) and navigate to **Develop > Functions & Assets**. If you're using the *legacy* Console, open the [**Functions** tab](https://www.twilio.com/console/functions/overview).
2. Functions are contained within **Services**. Click **[Create Service](https://www.twilio.com/console/functions/overview/services)** to create a new **[Service](/docs/serverless/functions-assets/functions/create-service)**.
3. Click **Add +** and select **Add Function** from the dropdown.
4. The Console creates a new [protected](/docs/serverless/functions-assets/visibility) Function that you can rename. The filename becomes the URL path of the Function.
5. Copy one of the example code snippets from this page and paste the code into your newly created Function. You can switch examples by using the dropdown menu in the code rail.
6. Click **Save**.
7. Click **Deploy All** to build and deploy the Function. After deployment, you can access your Function at `https://<service-name>-<random-characters>-<optional-domain-suffix>.twil.io/<function-path>`\
   For example: `test-function-3548.twil.io/hello-world`.

## Serverless Toolkit

The [Serverless Toolkit](/docs/labs/serverless-toolkit) lets you develop locally, deploy projects, and perform other tasks through the [Twilio CLI](/docs/twilio-cli/quickstart).

1. From the CLI, run `twilio serverless:init <YOUR-SERVICE-NAME> --empty` to bootstrap your local environment.
2. Go to your new project directory using `cd <YOUR-SERVICE-NAME>`.
3. In the `/functions` directory, create a JavaScript file whose name reflects the purpose of the Function. For example, `sms-reply.protected.js` for a [protected](/docs/serverless/functions-assets/visibility) Function intended to handle incoming SMS.
4. Add the code example of your choice to the file and save it. Note that a Function can only export a single handler. You need to create separate files to run or deploy multiple examples at once.

After you save the Function code, you can test it locally (and optionally tunnel requests to it using a tool like [ngrok](https://ngrok.com/)), or deploy it.

### Run your Function in local development

Run `twilio serverless:start` from your CLI to start the project locally. The Function(s) in your project are accessible from `http://localhost:3000/sms-reply`

* If you want to test a Function as a [Twilio webhook](/docs/usage/webhooks/getting-started-twilio-webhooks), run: `twilio phone-numbers:update <your Twilio phone number> --sms-url "http://localhost:3000/sms-reply"`\
  This automatically generates an ngrok tunnel from Twilio to your locally running Function, so you can start sending texts to it. You can apply the same process but with the `voice-url` flag instead to test with [Twilio Voice](/docs/voice).
* If your code does *not* connect to Twilio Voice or Messages as a webhook, start your dev server and start an ngrok tunnel in the same command with the `ngrok` flag. For example: `twilio serverless:start --ngrok=""`

### Deploy your Function

To deploy your Function and have access to live url(s), run `twilio serverless:deploy` from your CLI. This deploys your Function(s) to Twilio under a development Environment by default, where they can be accessed from:

`https://<service-name>-<random-characters>-dev.twil.io/<function-path>`

For example: `https://incoming-sms-examples-3421-dev.twil.io/sms-reply`

You can now invoke your Function with HTTP requests, configure it as the [webhook](/docs/usage/webhooks/getting-started-twilio-webhooks) for a Twilio phone number, call it from a Twilio Studio [**Run Function** Widget](/docs/studio/widget-library/run-function), and more.

With the Function created, we'll need to edit the boilerplate code that is generated for the Function—by default, it comes with some code to return TwiML. We're only going to return a joke. And it's a bad joke.

```js title="Return a Joke with a Twilio Function"
exports.handler = (context, event, callback) => {
  const joke = 'How many apples grow on a tree? They all do!';
  return callback(null, joke);
};
```

Copy the above code into the Twilio Functions code editor. Please, change the joke to something better. Press the **Save** button to save that code, and click **Deploy All** to deploy your Function.

## Call a Twilio Function from the Web

To call your new Function from the web, get the Function's URL by clicking the Copy URL icon next to the path, and then paste that URL into any web browser (you don't have to be authenticated with Twilio). You'll get a text response containing whatever you return from your Function!

## Call a Twilio Function from Android

We are going to use Google's open source [Volley](https://developer.android.com/training/volley/index.html) library to call our Twilio Function. Volley is a great choice, and provides built-in request classes for retrieving strings, JSON objects, and JSON Arrays.

Volley is not part of the Android SDK. You will need to include the Volley library in your `build.gradle` file as a dependency, like this:

```java
dependecies {
    ...
    compile 'com.android.volley:volley:1.0.0'
    ...
}
```

If you are using Android Studio, be sure to Sync your gradle file after this edit.

Don't forget to also put the INTERNET permission request into your **AndroidManifest.xml** file as well, or you will get an exception when you make an HTTP request.

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

The Volley `StringRequest` constructor takes the HTTP method used (`GET` in our case), the URL to retrieve, and two listeners—one for a successful response, and one if there is an error. The `onResponse` and `onErrorResponse` methods will be on the main (UI) thread, so you can modify the user interface. In our case, we are just going to log the responses to the console.

```java title="Call a Twilio Function from Android"
String url = "https://yourdomain.twil.io/joke";
StringRequest request = new StringRequest(Request.Method.GET,
    url,
    new Response.Listener<String>() {
        @Override
        public void onResponse(String response) {
            Log.d("APP", response);
        }
    },
    new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            Log.d("APP", error.getLocalizedMessage());
        }
    }
);
Volley.newRequestQueue(context).add(request);
```

## Return JSON from a Twilio Function

Our previous example Function returned plain text. You can also return JSON from a Twilio Function, by passing a JavaScript object or array to the `callback` function. For instance, we can create another Twilio Function to return a list of jokes, along with an id and a favorite count. Create a new Function with a path of `/jokes`.

```js title="A Twilio Function that Returns a JSON Array"
exports.handler = (context, event, callback) => {
  const knockKnock = { id: 1, text: 'Knock, knock', favorited: 37 };
  const chicken = {
    id: 2,
    text: 'Why did the chicken cross the road?',
    favorited: 12,
  };
  const jokes = [knockKnock, chicken];
  return callback(null, jokes);
};
```

## Parse JSON from a Twilio Function

From Android, we call this Function the same way that we did our first Function (don't forget to change the path to `/jokes`). We can use Volley's `JsonArrayRequest` object similarly to how we used `StringRequest` before.

```java title="Call a Twilio Function that returns JSON from Android"
String url = "https://yourdomain.twil.io/jokes";
JsonArrayRequest request = new JsonArrayRequest(url,
        new Response.Listener<JSONArray>() {

            @Override
            public void onResponse(JSONArray response) {
                Log.d("APP", response.toString());
            }
        },
        new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Log.d("APP", error.getLocalizedMessage());
            }
        }
);
Volley.newRequestQueue(context).add(request);
```

You've now seen how to run Node.js code as a Twilio Function, and how your mobile application can use this as a serverless backend to provide data for your application.

Where to go next? You could extend the Function to choose a random joke from that array. You can also use Twilio functionality from inside your Function, for instance to send an SMS, or to return an access token for Video, Chat, or Sync. Check out the [Programmable SMS Quickstart for Twilio Functions](/docs/serverless/functions-assets/quickstart/receive-sms) and [Programmable Voice Quickstart for Twilio Functions](/docs/serverless/functions-assets/quickstart/receive-call) for more quick introductions to these key features of Functions.