How to Get and send JSON with HttpClient in C#

using System.Net.Http.Json;

// Fetch JSON
var user = await httpClient.GetFromJsonAsync<User>($"https://localhost:12345/users/{userId}");

user.Age = 30;

// Submit JSON
await httpClient.PostAsJsonAsync<User>("https://localhost:12345/users/", user);

Note: If you are using a framework version prior to .NET 5, you need to install the System.Net.Http.Json package.

These extension methods leverage System.Text.Json for serialization, simplifying the process of handling JSON data.

To customize the serialization behavior, you can provide a JsonSerializerOptions object.

Installing the Required Package

For those using versions before .NET 5, make sure to install the System.Net.Http.Json NuGet package:

Install-Package System.Net.Http.Json

This command is run in the Package Manager Console (View > Other Windows > Package Manager Console).

Customizing JSON Serialization

If you need to customize how your objects are serialized, you can pass a JsonSerializerOptions object.

For instance, if you want to serialize enum values as their names instead of their underlying numeric values, use the following setup:

using System.Net.Http.Json;
using System.Text.Json;
using System.Text.Json.Serialization;

var user = new User()
{
    UserName = "john_doe",
    Status = UserStatus.Active,
    Age = 30,
    LastLogin = DateTimeOffset.Now
};

var options = new JsonSerializerOptions(JsonSerializerDefaults.Web);
options.Converters.Add(new JsonStringEnumConverter());

await httpClient.PostAsJsonAsync<User>("https://localhost:12345/users/", user, options);

This produces the following JSON, where the Status property uses the enum name instead of its value:

{
    "userName": "john_doe",
    "age": 30,
    "lastLogin": "2025-02-10T12:34:56.789Z",
    "status": "Active"
}

Using JsonSerializerDefaults.Web

If you don’t provide a JsonSerializerOptions object, System.Net.Http.Json uses the JsonSerializerDefaults.Web settings, which include:

var options = new JsonSerializerOptions()
{
    PropertyNameCaseInsensitive = true,
    PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
    NumberHandling = JsonNumberHandling.AllowReadingFromString
};

When creating your own options for customization, include JsonSerializerDefaults.Web to maintain these default settings.

If you want to use Newtonsoft.Json instead, you can fetch and deserialize JSON manually.

For example, How to retrieve a user’s data:

using Newtonsoft.Json;

var userId = "john_doe";
var response = await httpClient.GetAsync($"https://localhost:12345/users/{userId}");

response.EnsureSuccessStatusCode();

var json = await response.Content.ReadAsStringAsync();

var user = JsonConvert.DeserializeObject<User>(json);

Console.WriteLine($"User {user.UserName} is {user.Age} years old and has status {user.Status}.");

This is more verbose compared to the one-liner httpClient.GetFromJsonAsync<User>(url);.

Serializing an Object with Newtonsoft

To send an object as JSON using Newtonsoft, you can do the following:

using Newtonsoft.Json;

var user = new User()
{
    UserName = "john_doe",
    Status = UserStatus.Active,
    Age = 30,
    LastLogin = DateTimeOffset.Now
};

var json = JsonConvert.SerializeObject(user);

var response = await httpClient.PostAsync("https://localhost:12345/users/", 
    new StringContent(json, Encoding.UTF8, "application/json"));

response.EnsureSuccessStatusCode();

Consider using the Newtonsoft extension methods for HttpClient to streamline your code instead of repeating the manual serialization process.