Introduction

This tip/trick demonstrates a complete and easy solution on how to get JSON formatted data from a web service, and map (deserialize) it to custom .NET class for further usage.

As an example, we will use http://openexchangerates.org site which provides latest currency rates formatted as JSONdata. Latest daily rates will be retrieved from this here.

It outputs currency data in the following JSON format:

{
  "disclaimer": "This data is collected from various providers ...",
  "license": "Data collected from various providers with public-facing APIs ...",
  "timestamp": 1336741253,
  "base": "USD",
  "rates": {
    "AED": 3.6731,
    "AFN": 48.419998,
    "ALL": 107.949997,
    "AMD": 393.410004,
    "ANG": 1.79,
    "AOA": 94.949997,
    // ... more values ...
  }
}

So, how do we retrieve them through C# on the server side and use them? Read on to find out.

How To - Three Easy Steps

Step 1. Install Json.Net library

Json.NET library provides an easy, and de-facto, standard way to convert (serialize) .NET class to JSON data, and JSON data back to .NET class (deserialize). 

The easiest way to install Json.Net library into your .NET project is via NuGet Package Manager Console by running this command:

install-package Newtonsoft.Json

Alternatively, if you need to install it manually, download it from its project page on CodePlex.

Step 2. Create .NET class which will match JSON data format

If you are using Visual Studio 2012 you're in luck, since you can just paste a sample JSON data and it will create a class for you, To do that, first create a new class .cs file, select it in project explorer, than copy sample JSON data to clipboard, go to EDIT > Paste Special > Paste JSON as classes (thanks to Dave Kerr for this tip). More information on this feature here. 

If that won't work for you, or you'd prefer to do it yourself, you'll need to define .NET class manually. It must exactly match the format of JSON data provided to us by http://openexchangerates.org/latest.json:

public class CurrencyRates {
  public string Disclaimer { get; set; }
  public string License { get; set; }
  public int TimeStamp { get; set; }
  public string Base { get; set; }
  public Dictionary<string, decimal> Rates { get; set; }
}

Note that property names are not case sensitive, but the name has to exactly match the JSON one. Also, notice how "rates" JSON property is matched to a Dictionary<string, decimal>. If "rates" would have a singular value, they could alternatively be matched to an Array or IEnumerable.

Step 3. Create a method to retrieve JSON data and map it to .NET class

Now we will create the following universal method that can be re-used for any .NET class, where'T' represents any .NET class that you need JSON data to be mapped to:

using System.Net;
using Newtonsoft.Json;

// ...

private static T _download_serialized_json_data<T>(string url) where T : new() {
  using (var w = new WebClient()) {
    var json_data = string.Empty;
    // attempt to download JSON data as a string
    try {
      json_data = w.DownloadString(url);
    }
    catch (Exception) {}
    // if string with JSON data is not empty, deserialize it to class and return its instance 
    return !string.IsNullOrEmpty(json_data) ? JsonConvert.DeserializeObject<T>(json_data) : new T();
  }
}

Here, at first, an instance of WebClient() System.Net class (a part of the .NET) downloads data from the specific URL (http://openexchangerates.org/latest.json in our case) as a plain string.

Then, this string containing JSON data is mapped (deserialized) to any .NET class provided (CurrencyRates in our case).

Deserialization is done via Json.NET library's method JsonConvert.DeserializeObject<T>(json_data), which attempts to match all JSON fields to the same .NET class fields.

In this example, a call to a universal method _download_serialized_json_data<T>() can look like this:

var url = "http://openexchangerates.org/latest.json";
var currencyRates = _download_serialized_json_data<CurrencyRates>(url);

And that's it! Now you can do anything you need with the data you retrieved.

Good luck!

History

  • 6/4/12 - Initial publication