Web and Web APIs

The internet is one of the most—if not the most—impressive pieces of technology ever created. A reliable system connecting 4 billion machines, it has also served as a platform enabling enormous amounts of innovation. Today we’ll look at the web in as a provider of services or APIs that we can utilize when we create our own applications.

Note that there is no written part of this lab. Instead, we’ll expect you to find any required information using the internet itself.

You’ll work in pairs on today’s activity, and you should work with your partner for your final project. If you don’t have one you must join a group today. You have a 20-point project UI checkpoint due next week.

1. Exploring Web APIs (60 Minutes)

Web interfaces make it possible for us to easily incorporate powerful services and enormous amounts of information into our Android apps. Many of these interfaces are publicly-available, and in other cases free API keys are provided for experimentation and limited use.

1.1. Forking and Cloning the Lab12 Android Studio Project

We’ve set up an GitHub repository for Lab 12. It contains an Android Studio project that’s correctly configured for Lab 12. Getting access to it is similar to how you imported MP0. But you have to fork our repository first. If it’s not obvious how to do that, try following these instructions.

Note that you should import this using Android Studio, not IntelliJ.

1.2. Understanding Volley

Our starter code uses Google’s Volley library to make API requests. You may want to review its documentation as you examine our starter code.

The Lab 12 code base uses a button to initiate a web API call. You should finish the web UI so that it displays the results in the text box provided and uses the progress bar appropriately.

Here’s the key bit of code that is making the web API request:

JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(
        Request.Method.GET,
        "",
        null,
        new Response.Listener<JSONObject>() {
            @Override
            public void onResponse(final JSONObject response) {
                Log.d(TAG, response.toString());
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(final VolleyError error) {
                Log.w(TAG, error.toString());
            }
        });

Answer the following questions about the code above:

What kind of HTTP request is being made?
What is the URL being used?
What code runs if the request succeeds?
What code runs if the request fails?
If the request fails, how would you find out more information about why?

1.3. Adding URL Parameters to a Request

Some APIs, like this one, require that you add parameters to your URL. So if I wanted to get a quote for Apple Computer, Inc., which has symbol APPL, just issuing a GET request with this URL:

https://api.iextrading.com/1.0/stock/AAPL/batch

Returns an empty JSON array. Because, as their documentation explains, there is a required types request parameter. So, to request a quote my GET request URL would look like

https://api.iextrading.com/1.0/stock/AAPL/batch?types=quote

and to get both a quote and stock news

https://api.iextrading.com/1.0/stock/AAPL/batch?types=quote,news

1.4. Adding Data to a `POST` Request

When you use POST you’ll usually want to add some JSON data to the body of the request. Volley makes this quite easy. Here’s an example:

// Initialize a new JSONObject from a string. Note the escaping required.
final JSONObject jsonBody = new JSONObject("{\"type\":\"example\"}");
JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(
        Request.Method.POST,
        url,
        jsonBody,
        ...

Note that you can create a JSONObject from a String as shown, as long as it is valid JSON. You also have to escape (\") the double quotes inside the string literal.

1.5. Adding Headers to a Request

To authenticate with some APIs you must add your API key to the header of the HTTP message. For example, the documentation for the Microsoft Cognitive Services Computer Vision API specifies that you must add an API key to the headers with name Ocp-Apim-Subscription-Key.

Here’s an example of how to do that using Volley that also logs the parameters to the debugging output:

JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(
        Request.Method.GET,
        "",
        null,
        new Response.Listener<JSONObject>() {
            @Override
            public void onResponse(final JSONObject response) {
                Log.d(TAG, response.toString());
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(final VolleyError error) {
                Log.w(TAG, error.toString());
            }
        }) {
            @Override
            public Map<String, String> getHeaders() {
                Map<String, String>  params = new HashMap<String, String>();
                params.put("Ocp-Apim-Subscription-Key", "YOUR_API_KEY");
                Log.d(TAG, params.toString());
                return params;
            }
        };

1.6. Making Your Own API Calls

One of the things that makes learning how to use web APIs so powerful is that there are so many of them. So for this part of the lab we’ll ask you to use four different external web APIs to access different kinds of data. We suggest that you peruse this list of free public APIs that return JSON for inspiration, but you can also Google around for possible APIs to use.

You’ll also want to complete you starter application so that it both displays the JSON that is returned in the available text box and uses a Toast notification to indicate errors when something goes wrong. You should also continue to log errors and warnings using Android’s Logging system to aid your own development.

Choose four different web APIs to make the following kinds of requests. Note that this list above distinguishes between APIs that require authentication and those that do not

A GET that does not require authentication
A GET that does require authentication
A POST that does not require authentication
A POST that does require authentication

Review the instructions above as needed to determine how to add information to your GET and POST requests. But don’t get stuck on one particular API for too long. If it doesn’t seem to be working, try another one. You may also want to review this tutorial on the basics of API authentication.

2. Final Project UI and Planning (50 Minutes)

Use any remaining time in your lab section to work on your final project with your project partner.

During next week’s lab we’ll ask each group for a brief overview of their project and to demonstrate a working UI. This means that all UI elements should be in place and should be attached as needed to some kind of handler in each activity. Those handlers don’t have to do anything, yet: they can just log a message so that we know that they are working. Although you may want to keep going if you get to this point quickly.

If you need help with UI development please refer to Lab 12, or as on the forum.