Parsing API Data

Web APIs typically provide their data in a structured format, i.e. XML or JSON. To use this within a C# program you’ll need to either parse it or convert it into an object or objects.

The Joke of the Day API can provide either - we just need to specify our preference with a Accept header in our HTTP request. This header lets the server know what format(s) of data we are ready to process. XML is signified by the MIME type application/xml and JSON by application/json.

To set this (or any other header) in our WebRequest object, we use the Header property’s Add() method:

WebRequest request = WebRequest.Create("");
request.Headers.Add("Accept", "application/json");

For JSON, or:

WebRequest request = WebRequest.Create("");
request.Headers.Add("Accept", "application/xml");

For XML.

Parsing XML

Let’s start by examining the older format, XML. Assuming you have set the Accept header as discussed above, you will receive a response similar to (but with a different joke):

      <description>Joke of the day </description>
        <title>Signs for every job</title>
        In the front yard of a funeral home, "Drive carefully, we'll wait." On an electrician's truck, "Let us remove your shorts." Outside a radiator repair shop, "Best place in town to take a leak." In a non-smoking area, "If we see you smoking, we will assume you are on fire and take appropriate action." On a maternity room door, "Push, Push, Push." On a front door, "Everyone on the premises is a vegetarian except the dog." At an optometrist's office, "If you don't see what you're looking for, you've come to the right place." On a taxidermist's window, "We really know our stuff." On a butcher's window, "Let me meat your needs." On a butcher's window, "You can beat our prices, but you can't beat our meat." On a fence, "Salesmen welcome. Dog food is expensive." At a car dealership, "The best way to get back on your feet - miss a car payment." Outside a muffler shop, "No appointment necessary. We'll hear you coming." In a dry cleaner's emporium, "Drop your pants here." On a desk in a reception room, "We shoot every 3rd salesman, and the 2nd one just left." In a veterinarian's waiting room, "Be back in 5 minutes. Sit! Stay!" At the electric company, "We would be delighted if you send in your bill. However, if you don't, you will be." In a Beauty Shop, "Dye now!" In a Beauty Shop, "We curl up and Dye for you." On the side of a garbage truck, "We've got what it takes to take what you've got." (Burglars please copy.) In a restaurant window, "Don't stand there and be hungry, come in and get fed up." Inside a bowling alley, "Please be quiet. We need to hear a pin drop." In a cafeteria, "Shoes are required to eat in the cafeteria. Socks can eat any place they want."

We can parse this response with C#’s XmlDocument Class from the System.Xml namespace. First, we create an instance of the class, using our response text. We can use one of the XmlDocument.Load() overrides, which takes a stream, to process our response stream directly:

using Stream responseStream = response.GetStream() 
  XmlDocument xDoc = new XmlDocument();
  // TODO: get our joke!

Then we can query the XmlDocument for the tag we care about, i.e. response > contents > jokes > joke > text (the text of the joke). We use XPath syntax for this:

  var node = xDoc.SelectSingleNode("/response/contents/jokes/joke/text");

XPath is a query language, much like CSS selectors, which allow you to navigate a XML document in a lot of different ways. In this case, we are just finding the exact element based on its path. Then we can pull its value, and do something with it (such as logging it to the console):


Parsing JSON

JavaScript Object Notation (JSON) has become a popular format for web APIs, as it usually requires less characters than the corresponding XML, and is natively serializable from JavaScript making it extremely compatible with client-side web applications.

Assuming you have set the Accept header as discussed above, you will receive a response similar to (but with a different joke):

        "description":"Joke of the day ",
          "title":"Class With Claus",
          "text":"Q: What do you say to Santa when he's taking attendance at school?\nA: Present."
    "copyright":"2019-20 https:\/\/"

The C# system libraries provide JSON support in the System.Text.Json namespace using the JsonSerializer class. The default behavior of the deserializer is to deserialize into a JsonDocument composed of nested JsonElement objects - essentially, dictionaries of dictionaries. As with the XDocument, we can deserialize JSON directly from a Stream:

using Stream responseStream = response.GetStream() 
  JsonDocument jDoc = JsonSerializer.Deserialize(responseStream);
  // TODO: get our joke!

Then we can navigate from the root element (a JsonElement instance) down the nested path of key/value pairs, by calling GetProperty() to access each successive property, and then print the joke text to the console:

  var contents = jDoc.RootElement.GetProperty("contents");
  var jokes = contents.GetProperty("jokes");
  var jokeData = jokes[0];
  var joke = jokeData.GetProperty("joke");
  var text = joke.GetProperty("text");