Creating a Custom JsonConverter

Oct 13, 2025 by wbrum.org 33 views

Introduction

When working with APIs, it's common to encounter scenarios where specific data types need to be encoded or formatted in a particular way to ensure seamless communication between the client and server. In this case, we're dealing with GUIDs (Globally Unique Identifiers) that need to be encoded in response objects. To achieve this, we'll create a custom JsonConverter at the global level, which will enable us to encode GUIDs in a standardized manner.

Why Encode GUIDs?

GUIDs are widely used in various applications to uniquely identify objects, records, or entities. However, when these GUIDs are returned in response objects, they may not be in a format that's easily consumable by clients. Encoding GUIDs helps to standardize their representation, making it easier for clients to parse and utilize the data.

Creating a Custom JsonConverter

To create a custom JsonConverter, we'll need to implement the JsonConverter interface, which is part of the System.Text.Json namespace. This interface requires us to implement two methods: Read and Write.

GuidJsonConverter.cs

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

public class GuidJsonConverter : JsonConverter<Guid>
{
    public override Guid Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        // Read the GUID from the JSON string
        string guidString = reader.GetString();
        return new Guid(guidString);
    }

    public override void Write(Utf8JsonWriter writer, Guid value, JsonSerializerOptions options)
    {
        // Encode the GUID as a string
        string encodedGuid = value.ToString("N");
        writer.WriteStringValue(encodedGuid);
    }
}

In the above code, we've implemented the Read method to convert the GUID string from the JSON input to a Guid object. The Write method, on the other hand, takes a Guid object and encodes it as a string using the "N" format specifier, which represents the GUID in the format "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx".

Registering the Custom JsonConverter

To use our custom JsonConverter, we need to register it globally. We can do this by creating a new instance of the JsonSerializerOptions class and adding our custom converter to the Converters collection.

Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;
using System.Text.Json;

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllers(options =>
        {
            options.JsonOptions.JsonSerializerOptions.Converters.Add(new GuidJsonConverter());
        });
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        // ...
    }
}

In the above code, we've added our custom GuidJsonConverter to the JsonSerializerOptions instance and registered it globally using the AddControllers method.

Testing the Custom JsonConverter

Now that we've created and registered our custom JsonConverter, let's test it by creating a simple API controller that returns a RunViewModel object.

RunController.cs

using Microsoft.AspNetCore.Mvc;
using System;

public class RunController : ControllerBase
{
    [HttpGet]
    public IActionResult GetRun()
    {
        RunViewModel runViewModel = new RunViewModel
        {
            RunId = Guid.NewGuid(),
            RunnerId = Guid.NewGuid()
        };

        return Ok(runViewModel);
    }
}

In the above code, we've created a simple API controller that returns a RunViewModel object with two GUID properties: RunId and RunnerId. When we call the GetRun action, the GuidJsonConverter will be invoked to encode the GUIDs in the response object.

Conclusion

Introduction

In our previous article, we created a custom JsonConverter to encode GUIDs in response objects. In this article, we'll answer some frequently asked questions (FAQs) related to creating custom JsonConverters and encoding GUIDs.

Q: Why do I need to create a custom JsonConverter?

A: You don't necessarily need to create a custom JsonConverter to encode GUIDs. However, if you have specific requirements or constraints that cannot be met by the built-in JsonConverter implementations, creating a custom JsonConverter can be a good solution.

Q: What are the benefits of using a custom JsonConverter?

A: Using a custom JsonConverter provides several benefits, including:

Flexibility: You can implement custom logic to convert data types that are not supported by the built-in JsonConverter implementations.
Performance: Custom JsonConverters can be optimized for specific use cases, leading to improved performance.
Standardization: Custom JsonConverters can help standardize the representation of specific data types in your API responses.

Q: How do I know which data types to encode?

A: The decision to encode specific data types depends on your application's requirements and constraints. In general, you should consider encoding data types that:

Have a specific format: If a data type has a specific format that needs to be preserved, encoding it can help ensure consistency.
Are sensitive: If a data type contains sensitive information, encoding it can help protect it from unauthorized access.
Need to be standardized: If a data type needs to be standardized across different systems or applications, encoding it can help achieve consistency.

Q: Can I use a custom JsonConverter to encode other data types?

A: Yes, you can use a custom JsonConverter to encode other data types beyond GUIDs. The process of creating a custom JsonConverter is similar, regardless of the data type being encoded.

Q: How do I register a custom JsonConverter globally?

A: To register a custom JsonConverter globally, you can use the JsonSerializerOptions instance and add your custom converter to the Converters collection. Here's an example:

services.AddControllers(options =>
{
    options.JsonOptions.JsonSerializerOptions.Converters.Add(new CustomJsonConverter());
});

Q: Can I use a custom JsonConverter with other serialization libraries?

A: Yes, you can use a custom JsonConverter with other serialization libraries, such as Newtonsoft.Json. However, the process of creating and registering a custom JsonConverter may vary depending on the library being used.

Q: How do I troubleshoot issues with a custom JsonConverter?

A: To troubleshoot issues with a custom JsonConverter, you can:

Check the logs: Review the application logs to see if any errors or warnings are being generated.
Use debugging tools: Use debugging tools, such as Visual Studio's debugger, to step through the code and identify issues.
Test the custom JsonConverter: Test the custom JsonConverter in isolation to ensure it's working correctly.

Conclusion

In this article, we've answered some frequently asked questions related to creating custom JsonConverters and encoding GUIDs. By following these guidelines and best practices, you can create custom JsonConverters that meet your application's specific requirements and constraints.