What is JSON?

JSON - JavaScript Object Notation

JSON is a lightweight data-interchange format created as an alternative to XML for asynchronous communication between a client and the server providing data.

Benefits of JSON vs. XML

• lightweight
• self describing
• fairly easy to read

How is JSON data structured?

• Data is stored as key / value pairs
• Pairs are separated by commas (,)
• Curly braces ({}) hold objects, set of key / value pairs
• Square brackets ([]) hold arrays, an ordered collection of values
• Keys must be a string written with double quotes
• Values can be any of the following data types
• String
• Number
• Boolean (true/false)
• Null
• Date
• Object
• Array

Data Type Examples:

String:

{“name”:”Brian Spencer”}

Number:

{“age”: 21}

Boolean:

{“hasKids”:true}

Null:

{“ssn”:null}

Date (ISO 8601 format):

{“dob”:”1996-01-01T04:45:14”}

Object:

{“name”:”Brian Spencer”,”dob”:”1996-01-01T04:45:14”,”age”:21,”ssn”:null}

Array:

{“kids”:[“Lili”,”Alex”,”Ana”]}

What languages can Serialize and Deserialize JSON?

Here are a few languages that either include or have libraries or packages that can be used to serialize and deserialize JSON.

• JavaScript
• JSON object is built in
• Java
• org.json Package
• Python
• json library is included in the Python Standard Library as of version 2.6
• Objective-C and Swift
• NSJSONSerialization class
• C# and VB.Net
• DataContractJsonSerializer class, part of the System.Runtime.Serialization.Json namespace
• JavaScriptSerializer class, part of the System.Web.Script.Serialization namespace
• Newtonsoft JSON.Net

Code example:  Serialize and deserialize JSON using C# and DataContractJsonSerializer

[DataContract(Name="parent")]
public class Parent
{
    //DataMember Name and Order properties allow you to indicate what the name 
    //should be when the property or variable is serialized and what order 
    //the key/values should be in
    [DataMember(Name="name", Order=1)]
    public string Name { get; set; }

    [DataMember(Name = "age", Order=2)]
    public int Age { get; set; }

    [DataMember(Name = "hasKids", Order=4)]
    public bool HasKids { get; set; }

    //Do not serialize this property
    [IgnoreDataMember]
    public DateTime DOB { get; set; }

    [DataMember(Name = "dob", Order=3)]
    private string DOBISO;

    [DataMember(Order=10)]
    public string SSN;

    //Optional:  Do some work when serializing the object
    [OnSerializing]
    public void OnSerializing(StreamingContext context)
    {
        this.DOBISO = this.DOB.ToString("o"); //Convert date string to ISO 8601
    }

    //Optional: Do some work when deserializing the object
    [OnDeserialized]
    public void OnDeserialized(StreamingContext content)
    {
        this.DOB = DateTime.Parse(this.DOBISO);
    }
}
//Create the parent object and populate it's properties
Parent parent = new Parent();
parent.Name = "Brian Spencer";
parent.Age = 21;
parent.DOB = new DateTime(1996, 1, 1);
parent.HasKids = true;

string jsonString = string.Empty; //variable to hold the JSON string

//Create an instances of the DataContractJsonSerializer class
DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(Parent));

//Create an instance of the MemorySteam class to write the serialized object to
using (MemoryStream mem = new MemoryStream())
{
    //Serialize the parent object to memory
    ser.WriteObject(mem, parent);
    //write the JSON string in memory to the jsonString variable using UTF8 encoding
    jsonString = Encoding.UTF8.GetString(mem.ToArray(), 0, (int)mem.Length);
    //Close the memory stream
    mem.Close();
}
Console.WriteLine(jsonString);
//{"name":"Brian Spencer","age":21,"dob":"1996-01-01T00:00:00.0000000","hasKids":true,"SSN":null}

//Convering the JSON back to an object
Parent parentFromJson = (Parent)ser.ReadObject(new MemoryStream(Encoding.UTF8.GetBytes(jsonString)));

Return ISO 8601 dates when converting object to JSON using DataContractJsonSerializer

Below is an example of how to return a DataTime value in the ISO 8601 format when serializing an object using DataContractJsonSerializer.

[DataContract]
public class MyObjectWithDate
{
    [IgnoreDataMember]
    public DateTime MyDate { get; set; }

    [DataMember(Name = "mydate")]
    private string MyDateISO;

    [OnSerializing]
    public void OnSerializing(StreamingContext context)
    {
        this.MyDateISO = this.MyDate.ToString("o"); //Convert date string to ISO 8601
    }
}