How to Convert JsonElement to a Strongly-Typed Object in System.Text.Json?

ToObject equivalent method of System.Text.Json.JsonElement

Concept

In .NET Core 3, the Json.NET library provides the ToObject method, allowing JToken objects to be converted to strongly typed classes. This article explores the equivalent method of deserializing JsonElement objects in System.Text.Json.

Solution

In .NET 6 and above:

JsonSerializer has added extension methods to deserialize directly from JsonElement and JsonDocument objects:

public static TValue? Deserialize<TValue>(this JsonDocument document, JsonSerializerOptions? options = null);
public static TValue? Deserialize<TValue>(this JsonElement element, JsonSerializerOptions? options = null);

In .NET 5 and earlier:

There is a workaround that can be used to improve performance:

public static T ToObject<T>(this JsonElement element, JsonSerializerOptions options = null)
{
    var bufferWriter = new ArrayBufferWriter<byte>();
    using (var writer = new Utf8JsonWriter(bufferWriter))
        element.WriteTo(writer);
    return JsonSerializer.Deserialize<T>(bufferWriter.WrittenSpan, options);
}

Example

var str = ""; // 一些 JSON 字符串
var jDoc = JsonDocument.Parse(str);
var myClass = jDoc.RootElement.GetProperty("SomeProperty").Deserialize<SomeClass>();

Attention

• Release the JsonDocument object to release memory resources.
• Extension methods were added to JsonNode in .NET 6 for similar deserialization functionality.
• The workaround performs better because it avoids unnecessary string conversions.

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