.NET Core 3 Fast Built-in JSON Support

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.NET users have largely relied on Newtonsoft.Json and other popular JSON libraries, which continue to be good choices. Newtonsoft.Json uses .NET strings as its base datatype, which is UTF-16 under the hood.

System.Text.Json

The System.Text.Json is built-in as part of the shared framework for .NET Core 3.0 and later versions.

  • It provides functionality for serializing to and deserializing from JavaScript Object Notation (JSON).
  • The library design emphasizes high performance and low memory allocation over an extensive feature set.
  • The built-in UTF-8 support optimizes the process of reading and writing JSON text encoded as UTF-8, which is the most prevalent encoding for data on the web and files on disk.
  • The library also provides classes for working with an in-memory document object model (DOM). This feature enables random read-only access to the elements in a JSON file or string.

For earlier framework versions, install the System.Text.Json NuGet package.

To serialize to UTF-8, call the JsonSerializer.SerializeToUtf8Bytes method as shown below.

public class Customer
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string Address { get; set; }
};

public static void Example1()
{
    Customer customer = new Customer()
    {
        Name = "Mark",
        Age = 40,
        Address = "22 Ashdown"
    };

    byte[] jsonUtf8Bytes = JsonSerializer.SerializeToUtf8Bytes(customer);

    Console.WriteLine(jsonUtf8Bytes);
}

To pretty-print the JSON output, set JsonSerializerOptions.WriteIndented to true as shown below.

public class Customer
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string Address { get; set; }
};

public static void Example2()
{
    Customer customer = new Customer()
    {
        Name = "Mark",
        Age = 40,
        Address = "22 Ashdown"
    };

    var options = new JsonSerializerOptions
    {
        WriteIndented = true
    };
    var jsonUtf8Bytes = JsonSerializer.Serialize(customer, options);

    Console.WriteLine(jsonUtf8Bytes);
}


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