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.Net Core Sample Example On HttpClientFactory Basic Implementation With HttpRequestMessage Object.



In this article, we are going to see the HTTP client factory's basic implementation technique to consume an API in our .Net Core application. Click here to understand how HttpClientFactory works.

Create A Sample API Project:

Now let's create a .net core web API sample project in which we are going to consume another API(Third-party API) using HttpClientFactory. You can create your sample project using editors like Visual Studio 2019 or Visual Studio Code.

Test API To Consume:

Let's consume a free Rest API to consume for our leaning process. There a lot of free developer API for learning purposes. Here we are going to use JSONPlaceholder.
JSONPlaceholder:

Guide :- https://jsonplaceholder.typicode.com/guide.html

Endpoints:-
1.https://jsonplaceholder.typicode.com/users/1/todos (Todos endpoint)
2.https://jsonplaceholder.typicode.com/users/1/albums (Albums endpoint)
3.https://jsonplaceholder.typicode.com/albums/1/photos (Photos endpoint)
4.https://jsonplaceholder.typicode.com/users/1/posts (Posts endpoint)
5.https://jsonplaceholder.typicode.com/posts/1/comments (Comments endpoint)
Here in our sample, we are going to consume Todos's endpoint from the JSONPlaceholder test API.

Register HttpClient:

To use HttpClientFactoy as an injectable service we need to configure the HttpClient extension method in the startup.cs file.
Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
	// code hidden for display purpose
	services.AddHttpClient();
}

Inject HttpClientFactory:

Let's create a web API controller that has HttpClientFactory injected.
Controllers/TodosController.cs:
using System.Net.Http;
using Microsoft.AspNetCore.Mvc;

namespace TestApi.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class TodosController : ControllerBase
    {
        private readonly IHttpClientFactory _httpClientFactory;
        public TodosController(IHttpClientFactory httpClientFactory)
        {
            _httpClientFactory = httpClientFactory;
        }
    }
}

Todos Model Object:

Now let's create a model object Todos that represents the payload object of third-party API which we will consume in upcoming steps.
Models/Todos.cs:
namespace TestApi.Models
{
    public class Todos
    {
        public int UserId { get; set; }
        public int Id { get; set; }
        public string Title { get; set; }
        public bool Completed { get; set; }
    }
}

HttpRequestMessage Object:

System.Net.Http.HttpRequestMessage object that comes with overloaded constructors where we can pass our configuration to make an external request. This HttpRequeMessage object will be used by HttpClient to make an external API call. HttpRequestMessage can be configured with an API endpoint,
Http verb type, headers, token information, etc. In simple words, we will prepare HttpRequesMessage with all configuration inputs to make an API call.

Get Action Method:

Let's create get action method endpoint that is going to consume a third-party Todos API list.
Controllers/TodosController:
using System.Collections.Generic;
using System.Net.Http;
using System.Text.Json;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using TestApi.Models;

namespace TestApi.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class TodosController : ControllerBase
    {
        [HttpGet]
        [Route("get-all")]
        public async Task<IActionResult> GetAllAsync()
        {
            var request = new HttpRequestMessage(HttpMethod.Get, "https://jsonplaceholder.typicode.com/users/1/todos");

            var httpClient = _httpClientFactory.CreateClient();

            var response = await httpClient.SendAsync(request);

            if (!response.IsSuccessStatusCode)
            {
                return NotFound();
            }

            var responseString = await response.Content.ReadAsStringAsync();
            var options = new JsonSerializerOptions
            {
                PropertyNameCaseInsensitive = true
            };
            List<Todos> todos = JsonSerializer.Deserialize<List<Todos>>(responseString, options);
            return Ok(todos);
        }
    }
}
  • #L18 at this line instantiated HttpRequestMessage object. HttpRequestMessage instance comes with multiple constructors, here we are passing the HttpVerb type of action and the third-party endpoint of Todos.
  • #L20 at this line creating HttpClient object using the HttpClientFactory.
  • #L22 at this line we are making an API call by sending the HttpRequestMessage object as an input parameter to the HttpClient SendAsync method.
  • #L24 at this line we are checking our API call success or not.
  • #L29 at this line we are reading API response as string content.
  • #L30-L33 JsonSerilizerOptions object initialized with a configuration of ignoring case sensitive of payload.
  • #L34 JsonSerializer object used to deserialize our string response to type Todo object collection.
Run the application and access the endpoint and output shows as below.

Post Action Method:

Post endpoint generally used for both creating and updating the records. The 'HttpRequestMessage.Content' property accepts the stringified payload. Using 'System.Net.Http.StringContent' instance is used to generate the stringified payload.
Controller/TodosController.cs:
using System.Collections.Generic;
using System.Net.Http;
using System.Text;
using System.Text.Json;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using TestApi.Models;

namespace TestApi.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class TodosController : ControllerBase
    {
		// code hidden for display purpose

        [HttpPost]
        [Route("create")]
        public async Task<IActionResult> Post(Todos newTodos)
        {
            var newTodosJson = JsonSerializer.Serialize<Todos>(newTodos);

            var request = new HttpRequestMessage(HttpMethod.Post, "https://jsonplaceholder.typicode.com/users/1/todos");

            request.Content = new StringContent(newTodosJson, Encoding.UTF8, "application/json");

            var httpClient = _httpClientFactory.CreateClient();

            var response = await httpClient.SendAsync(request);

            if (!response.IsSuccessStatusCode)
            {
               return Ok(new{ Message = "Failed"});
            }

            return Ok(new {Message = "Success"});
        }

    }
}
  • #L21 'System.Text.Json.JsonSerializer.Serialize<T>' is used to convert a Type object to a string. So here we converting our Todos post object to a string.
  • #L23 'System.Net.Http.HttpMethod.Post' method determines the API call as 'Post' call. Here we are passing call type and URL as input parameters to the HttpRequestMessage constructor.
  • #L24 To send payload for the post API call, HttpRequestMessage.Content property of type 'System.Net.Http.HttpConent' which accepts the payload. Now to send our string payload we are going to use the 'System.Net.Http.StringContent' object which inherits the 'System.Net..Http.HttpContent'. 
Let's test the post endpoint as below.

Delete Action Method:

The delete action method is to delete the records. For record deletion no need to post the entire record payload to the server, so sending id(mostly primary key unique identifier to the record) is enough for the deletion endpoint in general.
Note:
Todo endpoint returning 404 not found. So to understand deletion endpoint succesfully here in the sample below we are going to use Post endpoint.
Controllers/TodosController.cs:
using System.Collections.Generic;
using System.Net.Http;
using System.Text;
using System.Text.Json;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using TestApi.Models;

namespace TestApi.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class TodosController : ControllerBase
    {
        [HttpDelete]
        [Route("delete")]
        public async Task<IActionResult> Delete(int id)
        {
            var request = new HttpRequestMessage(HttpMethod.Delete, $"https://jsonplaceholder.typicode.com/posts/{id}");

            var httpClient = _httpClientFactory.CreateClient();

            var response = await httpClient.SendAsync(request);

            if (!response.IsSuccessStatusCode)
            {
                return Ok(new {Message = "Failed To Delete Todo"});
            }
            return Ok(new {Message ="Successfully Deleted Todo"});
        }

    }
}
Now run the application and the output shows as below.

Wrapping Up:

Hopefully, I think this article delivered some useful information about the HttpClientFactory basic implementation using the HttpRequestMessage object. I love to have your feedback, suggestions, and better techniques in the comment section below.

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