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Use C# to get JSON Data from the Web and Map it to .NET Class => Made Easy!

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12 Feb 2014CPOL2 min read 807.1K   120   49
Easy steps on how to get JSON formatted data from a web service, deserialize it, and map it to custom local class for further usage

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.

Sample Data

As an example, we will use https://openexchangerates.org service which provides latest currency rates formatted as JSON data. Here is a sample of how that data looks like:  

JSON
{
  "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 by openexchangerates.org:  

C#
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 <code><code>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:

C#
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 <a href="http://msdn.microsoft.com/en-us/library/system.net.webclient.aspx">WebClient()</a> System.Net class (a part of the .NET) downloads data from the specific URL 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:  

C#
var url = "https://openexchangerates.org/api/latest.json?app_id=YOUR_APP_ID ";
var currencyRates = _download_serialized_json_data<CurrencyRates>(url); 

(Please note: if you want to use data provided by openexchangerates.org, first you need to get your unique App Id here: https://openexchangerates.org/signup/free^, than replace YOUR_APP_ID in the sample above.) 

Final Note 

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

Good luck!

History

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Web Developer
United States United States
Coding is awesome!

Comments and Discussions

 
QuestionMixed JSon to Object Pin
Rupak Kr D7-Oct-12 3:27
Rupak Kr D7-Oct-12 3:27 
AnswerRe: Mixed JSon to Object Pin
Mikhail-T7-Oct-12 7:05
Mikhail-T7-Oct-12 7:05 
GeneralRe: Mixed JSon to Object Pin
Rupak Kr D7-Oct-12 10:12
Rupak Kr D7-Oct-12 10:12 
GeneralRe: Mixed JSon to Object Pin
Mikhail-T9-Oct-12 11:14
Mikhail-T9-Oct-12 11:14 
GeneralRe: Mixed JSon to Object Pin
Rupak Kr D24-Apr-14 5:21
Rupak Kr D24-Apr-14 5:21 
GeneralMy vote of 5 Pin
Manoj Kumar Choubey18-Jul-12 20:49
professionalManoj Kumar Choubey18-Jul-12 20:49 
QuestionWhy ? DataContractJsonSerializer works fine. Pin
Nicolas Dorier6-Jun-12 4:01
professionalNicolas Dorier6-Jun-12 4:01 
AnswerRe: Why ? DataContractJsonSerializer works fine. Pin
Mikhail-T6-Jun-12 6:37
Mikhail-T6-Jun-12 6:37 
Thumbs Up | :thumbsup: Great question!

For starters, I only work with MVC framework web applications, and honestly, I have very little idea about WCF programming))

After looking at samples of DataContractJsonSerializer in this example: http://msdn.microsoft.com/en-us/library/bb410770.aspx[^], It looks like DataContractJsonSerializer might be better suited for WCF applications, since it works directly with MemoryStream, which is rarely needed in web application.

Also, to serialize a class to Json in DataContractJsonSerializer looks like this:
MemoryStream stream1 = new MemoryStream();
DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(CurrencyRates));
ser.WriteObject(stream1, currencyRates)

And to deserialize:
CurrencyRates currencyRates = (CurrencyRates)ser.ReadObject(stream1);

According to this reference[^] it can read only Stream and XmlReader, which might need further conversions from other data types.

The other thing about Json.Net - most operations can be done in one line.
Serialize:
string json = JsonConvert.SerializeObject(currencyRates);

Deserialize:
CurrencyRates currencyRates = JsonConvert.DeserializeObject<CurrencyRates>(json);

So code is cleaner, more readable, and easier to use.

Also, main reason for me to prefer Json.Net, is that it will be shipped as a part of Microsoft MVC 4 framework[^], which alone is a sign of recognition of Json.Net as a good alternative for serialization needs, at least on the web application development front.

And finally, Json.Net is supposed to be much faster than DataContractJsonSerializer according to performance comparison here: http://james.newtonking.com/pages/json-net.aspx[^], which is good for web applications, where speed is crucial.

In addition, here - http://stackoverflow.com/questions/4826742/json-net-vs-datacontractjsonserializer[^] is some interesting comparison of Json.Net and DataContractJsonSerializer.

What do you think?
GeneralRe: Why ? DataContractJsonSerializer works fine. Pin
Nicolas Dorier6-Jun-12 7:14
professionalNicolas Dorier6-Jun-12 7:14 
GeneralMy vote of 5 Pin
Othello744-Jun-12 21:40
Othello744-Jun-12 21:40 
GeneralRe: My vote of 5 Pin
Mikhail-T5-Jun-12 6:17
Mikhail-T5-Jun-12 6:17 
GeneralMy vote of 5 Pin
parvus4-Jun-12 11:30
parvus4-Jun-12 11:30 
GeneralRe: My vote of 5 Pin
Mikhail-T4-Jun-12 11:47
Mikhail-T4-Jun-12 11:47 

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