Comparing JSON Libraries in .NET: Newtonsoft.Json vs. System.Text.Json

When working with JSON in .NET, two popular libraries are Newtonsoft.Json (also known as Json.NET) and System.Text.Json. Below, we compare their usage for reading and parsing JSON data.

1. Newtonsoft.Json

Reading and Parsing JSON

Installation:

Install-Package Newtonsoft.Json

Example: Deserialize JSON to Object

using Newtonsoft.Json;

public class Token
{
    public string? AccessToken { get; set; }
    public string? RefreshToken { get; set; }
    public int ExpiresIn { get; set; }
}

string json = "{ 'access_token': 'abc123', 'refresh_token': 'def456', 'expires_in': 3600 }";
Token token = JsonConvert.DeserializeObject<Token>(json);

Console.WriteLine(token.AccessToken); // Output: abc123

Example: Reading JSON from a File

string jsonContent = File.ReadAllText("token.json");
Token token = JsonConvert.DeserializeObject<Token>(jsonContent);

Example: Using JObject for Dynamic Access

using Newtonsoft.Json.Linq;

string json = "{ 'access_token': 'abc123', 'refresh_token': 'def456', 'expires_in': 3600 }";
JObject tokenData = JsonConvert.DeserializeObject<JObject>(json);
string accessToken = tokenData["access_token"]?.Value<string>();

2. System.Text.Json

Reading and Parsing JSON

Installation:
System.Text.Json is included in .NET Core 3.0 and later versions, so no additional installation is needed.

Example: Deserialize JSON to Object

using System.Text.Json;

public class Token
{
    public string? AccessToken { get; set; }
    public string? RefreshToken { get; set; }
    public int ExpiresIn { get; set; }
}

string json = "{ \"access_token\": \"abc123\", \"refresh_token\": \"def456\", \"expires_in\": 3600 }";
Token token = JsonSerializer.Deserialize<Token>(json);

Console.WriteLine(token.AccessToken); // Output: abc123

Example: Reading JSON from a File

string jsonContent = File.ReadAllText("token.json");
Token token = JsonSerializer.Deserialize<Token>(jsonContent);

Example: Using JsonDocument for Dynamic Access

using System.Text.Json;

string json = "{ \"access_token\": \"abc123\", \"refresh_token\": \"def456\", \"expires_in\": 3600 }";
using JsonDocument doc = JsonDocument.Parse(json);
JsonElement root = doc.RootElement;
string accessToken = root.GetProperty("access_token").GetString();

Comparison Summary

Feature	Newtonsoft.Json	System.Text.Json
Installation	Requires separate NuGet package	Built-in with .NET Core 3.0+
Deserialization	JsonConvert.DeserializeObject<T>()	JsonSerializer.Deserialize<T>()
Dynamic Access	JObject for flexible JSON access	JsonDocument for read-only access
Null Handling	More configurable options	Default ignore nulls with options
Performance	Slower than System.Text.Json	Generally faster and more efficient

Why AOT Needs to Use System.Text.Json

Ahead-Of-Time (AOT) Compilation is a technique used to improve performance by compiling code before runtime. System.Text.Json is designed to work seamlessly with AOT in .NET, providing the following benefits:

1. Reduced Memory Footprint: System.Text.Json is more lightweight, which helps in minimizing memory usage during compilation.

2. Faster Startup Times: AOT compilation with System.Text.Json can lead to faster application startup times because the JSON handling is optimized and compiled ahead of time.

3. Native Support: Being a part of the .NET core libraries, System.Text.Json is optimized for performance and compatibility with AOT compilation, reducing the risk of runtime issues compared to third-party libraries like Newtonsoft.Json.

4. Enhanced Performance: System.Text.Json typically offers better performance due to optimizations for serialization and deserialization, which is critical for applications that rely heavily on JSON data.

Conclusion

Both Newtonsoft.Json and System.Text.Json have their strengths. Use Newtonsoft.Json for complex scenarios and flexibility, and consider System.Text.Json for better performance, native support in .NET Core, and seamless integration with AOT compilation.