Call a JSON Web Service

This article demonstrates how to consume the Airport Service of the Federal Aviation Administration using the standard Android HTTP client API and the standard Android JSON parser. The FAA offers a tutorial describing their web services.

While this article includes code snippets only, the full code sample is included in dot42 update 1.0.0.61 or higher. See folder [MyDocuments]\dot42\Samples\Various\AirportInfo.

Send a GET request to the Airport Service

To get the airport status for airport OAK, including known delays and weather data, you would make a GET request to the following URL:

http://services.faa.gov/airport/status/OAK?format=application/json

The above URL encodes two input arguments: First, the three letter airport code (in this case OAK). Second, the format of the data that you would like to get back (in this case JSON).

The following code makes this request:

string iataCode = "OAK";
var uri = string.Format("http://services.faa.gov/airport/status/{0}?format=application/json", iataCode);
var client = AndroidHttpClient.NewInstance("AirportInfo");
var request = new HttpGet(uri);
var response = client.Execute(request); // send the request

Parse the HTTP response

When the above request is made to the service, it will return a response consisting of plain text formatted according the JSON format. Android offers class JSONObject to parse the name/value pairs.

First, we must extract the JSON string from the response:

var content = response.GetEntity().GetContent();
var reader = new BufferedReader(new InputStreamReader(content));
var builder = new StringBuilder();
string line;
while ((line = reader.ReadLine()) != null)
{
  builder.Append(line);
}
string jsonString = builder.ToString();

Then we wrap a JSONObject around the string:

JSONObject json = new JSONObject(jsonString);

And now we can query named values like this:

string state= json.GetString("state");
string city = json.GetString("city");

The full code

The full code sample is included in dot42 update 1.0.0.61 or higher. See folder [MyDocuments]\dot42\Samples\Various\AirportInfo.