System.Text.Json and new built-in JSON support in .NET Core

July 24, 2019 Comment on this post [10] Posted in ASP.NET | DotNetCore | Javascript

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In a world where JSON (JavaScript Object Notation) is everywhere it's long been somewhat frustrating that .NET didn't have built-in JSON support. JSON.NET is great and has served us well but it's remained a 3rd party dependency for basic stuff like an ASP.NET web site or a simple console app.

Back in 2018 plans were announced to move JSON into .NET Core 3.0 as an intrinsic supported feature, and while they're at it, get double the performance or more with Span<T> support and no memory allocations. ASP.NET in .NET Core 3.0 removes the JSON.NET dependency but still allows you to add it back in a single line if you'd like.

NOTE: This is all automatic and built in with .NET Core 3.0, but if you’re targeting .NET Standard or .NET Framework. Install the System.Text.Json NuGet package (make sure to include previews and install version 4.6.0-preview6.19303.8 or higher). In order to get the integration with ASP.NET Core, you must target .NET Core 3.0.

It's very clean as well. Here's a simple example.

using System;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace verysmall
{
    class WeatherForecast
    {
        public DateTimeOffset Date { get; set; }
        public int TemperatureC { get; set; }
        public string Summary { get; set; }
    }
    
    class Program
    {
        static void Main(string[] args)
        {
            var w = new WeatherForecast() { Date = DateTime.Now, TemperatureC = 30, Summary = "Hot" };
            Console.WriteLine(JsonSerializer.Serialize<WeatherForecast>(w));
        }
    }
}

The default options result in minified JSON as well.

{"Date":"2019-07-27T00:58:17.9478427-07:00","TemperatureC":30,"Summary":"Hot"}

Of course, when you're returning JSON from a Controller in ASP.NET it's all automatic and with .NET Core 3.0 it'll automatically use the new System.Text.Json unless you override it.

Here's an example where we pull out some fake Weather data (5 randomly created reports) and return the array.

[HttpGet]
public IEnumerable<WeatherForecast> Get()
{
    var rng = new Random();
    return Enumerable.Range(1, 5).Select(index => new WeatherForecast
    {
        Date = DateTime.Now.AddDays(index),
        TemperatureC = rng.Next(-20, 55),
        Summary = Summaries[rng.Next(Summaries.Length)]
    })
    .ToArray();
}

The application/json is used and JSON is returned by default. If the return type was just string, we'd get text/plain. Check out this YouTube video to learn more details about System.Text.Json works and how it was designed. I'm looking forward to working with it more!

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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.