JSON (System.Text.Json, Read and Write)Use the System.Text.Json namespace to read in, and output, JSON formatted text. Understand classes and generic methods.
JSON. Optimized JSON handling is increasingly important in developing programs. New versions of .NET include the System.Text.Json namespace, which helps matters.
Generic methods. To parse in JSON, we need to write special, custom classes that match the JSON data we are parsing. These classes are then populated automatically by .NET.
Read example. Reading JSON data is done with the Deserialize() method. We must first include System.Text.Json, and we must have a class that matches the data format.
Info The property names (like Bird or Cat) must match the key names in the JSON string. And the types of the data must also match.
Tip This program was first developed for .NET 5.0. This release of .NET has optimized JSON handling.
using System;
using System.Text.Json;
public class AnimalData
{
public int Bird { get; set; }
public string Cat { get; set; }
}
class Program
{
const string _example = @"{""Bird"":10,""Cat"":""Fuzzy""}";
static void Main()
{
var result = JsonSerializer.Deserialize<AnimalData>(_example);
Console.WriteLine("BIRD JSON: {0}", result.Bird);
Console.WriteLine("CAT JSON: {0}", result.Cat);
}
}BIRD JSON: 10
CAT JSON: Fuzzy
Write example. To write JSON from a class in memory, we must call the Serialize method. We can specify a type parameter to the generic Serialize method.
Result The program creates an AnimalData with 2 properties set, and then writes it to a JSON string and prints the string.
using System;
using System.Text.Json;
public class AnimalData
{
public int Bird { get; set; }
public string Cat { get; set; }
}
class Program
{
static void Main()
{
// Create new object with 2 properties.
var data = new AnimalData(){ Bird = 20, Cat = "Soft" };
// Call Serialize.
var result = JsonSerializer.Serialize<AnimalData>(data);
Console.WriteLine("JSON RESULT: {0}", result);
}
}JSON RESULT: {"Bird":20,"Cat":"Soft"}
List. Often JSON contains lists. We can read JSON text directly into a List with Deserialize. We place a List property on a class with an identifier that matches the JSON key.
Tip An array could be used to store the data in this example. Try changing List<int> to int[].
using System;
using System.Collections.Generic;
using System.Text.Json;
class Result
{
public List<int> Values { get; set; }
}
class Program
{
const string _text = @"{""Values"":[10, 20, 30]}";
static void Main()
{
var result = JsonSerializer.Deserialize<Result>(_text);
// Get list property from class.
var list = result.Values;
Console.WriteLine("RESULT LIST: {0}", string.Join(",", list));
}
}RESULT LIST: 10,20,30
Dictionary. We can parse in a Dictionary from JSON—no special classes are needed. This code does not rely on property names to store JSON key value pairs—it just uses Dictionary keys.
using System;
using System.Collections.Generic;
using System.Text.Json;
class Program
{
const string _text = @"{""One"":1,""Two"":2}";
static void Main()
{
var result = JsonSerializer.Deserialize<Dictionary<string, int>>(_text);
// Loop over dictionary from JSON.foreach (var item in result)
{
Console.WriteLine("ITEM: {0}, {1}", item.Key, item.Value);
}
}
}ITEM: One, 1
ITEM: Two, 2
A summary. With an optimized JSON handling library, we can process this convenient text format more easily. We invoke Deserialize and Serialize in our programs.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
