Consume Web API in .NET using HttpClient:

The .NET 2.0 included WebClient class to communicate with web server using HTTP protocol. However, WebClient class had some limitations. The .NET 4.5 includes HttpClient class to overcome the limitation of WebClient. Here, we will use HttpClient class in console application to send data to and receive data from Web API which is hosted on local IIS web server. You may use HttpClient in other .NET applications also such as MVC Web Application, windows form application, windows service application etc.

Let's see how to consume Web API using HttpClient in the console application.

We will consume the following Web API created in the previous section.

Example: Web API Controller

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;

namespace MyWebAPI.Controller
{
    public class StudentController : ApiController
    {
        public IHttpActionResult GetAllStudents(bool includeAddress = false)
        {
            IList<StudentViewModel> students = null;

            using (var ctx = new SchoolDBEntities())
            {
                students = ctx.Students.Include("StudentAddress").Select(s => new StudentViewModel()
                {
                    Id = s.StudentID,
                    FirstName = s.FirstName,
                    LastName = s.LastName,
                    Address = s.StudentAddress == null || includeAddress == false ? null : new AddressViewModel()
                    {
                        StudentId = s.StudentAddress.StudentID,
                        Address1 = s.StudentAddress.Address1,
                        Address2 = s.StudentAddress.Address2,
                        City = s.StudentAddress.City,
                        State = s.StudentAddress.State
                    }
                }).ToList<StudentViewModel>();
            }


            if (students.Count == 0)
            {
                return NotFound();
            }

            return Ok(students);

        }

        public IHttpActionResult PostNewStudent(StudentViewModel student)
        {
            if (!ModelState.IsValid)
                return BadRequest("Not a valid data");

            using (var ctx = new SchoolDBEntities())
            {
                ctx.Students.Add(new Student()
                {
                    StudentID = student.Id,
                    FirstName = student.FirstName,
                    LastName = student.LastName
                });

                ctx.SaveChanges();
            }

            return Ok();
        }

        public IHttpActionResult Put(StudentViewModel student)
        {
            if (!ModelState.IsValid)
                return BadRequest("Not a valid data");

            using (var ctx = new SchoolDBEntities())
            {
                var existingStudent = ctx.Students.Where(s => s.StudentID == student.Id).FirstOrDefault<Student>();

                if (existingStudent != null)
                {
                    existingStudent.FirstName = student.FirstName;
                    existingStudent.LastName = student.LastName;

                    ctx.SaveChanges();
                }
                else
                {
                    return NotFound();
                }
            }

            return Ok();
        }


        public IHttpActionResult Delete(int id)
        {
            if (id <= 0)
                return BadRequest("Not a valid studet id");

            using (var ctx = new SchoolDBEntities())
            {
                var student = ctx.Students
                    .Where(s => s.StudentID == id)
                    .FirstOrDefault();

                ctx.Entry(student).State = System.Data.Entity.EntityState.Deleted;
                ctx.SaveChanges();
            }

            return Ok();
        }
    }
}

Step 1:

First, create a console application in Visual Studio 2013 for Desktop.

Step 2:

Open NuGet Package Manager console from TOOLS -> NuGet Package Manager -> Package Manager Console and execute following command.

Install-Package Microsoft.AspNet.WebApi.Client

Step 3:

Now, create a Student model class because we will send and receive Student object to our Web API.

Example: Model Class

public class Student
{
    public int Id { get; set; }
    public string Name { get; set; }
}

Send GET Request:

The following example sends an HTTP GET request to Student Web API and displays the result in the console.

Example: Send HTTP GET Request using HttpClient

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net.Http;
using System.Net.Http.Headers;

namespace HttpClientDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var client = new HttpClient())
            {
                client.BaseAddress = new Uri("http://localhost:60464/api/");
                //HTTP GET
                var responseTask = client.GetAsync("student");
                responseTask.Wait();

                var result = responseTask.Result;
                if (result.IsSuccessStatusCode)
                {

                    var readTask = result.Content.ReadAsAsync<Student[]>();
                    readTask.Wait();

                    var students = readTask.Result;

                    foreach (var student in students)
                    {
                        Console.WriteLine(student.Name);
                    }
                }
            }
            Console.ReadLine();
        }        
    }
}

Let's understand the above example step by step.

First, we have created an object of HttpClient and assigned the base address of our Web API. The GetAsync() method sends an http GET request to the specified url. The GetAsync() method is asynchronous and returns a Task. Task.wait() suspends the execution until GetAsync() method completes the execution and returns a result.

Once the execution completes, we get the result from Task using Task.result which is HttpResponseMessage. Now, you can check the status of an http response using IsSuccessStatusCode. Read the content of the result using ReadAsAsync() method.

Thus, you can send http GET request using HttpClient object and process the result.

Send POST Request:

Similarly, you can send HTTP POST request using PostAsAsync() method of HttpClient and process the result the same way as GET request.

The following example send http POST request to our Web API. It posts Student object as json and gets the response.

Example: Send HTTP POST Request using HttpClient

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net.Http;
using System.Net.Http.Headers;

namespace HttpClientDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            var student = new Student() { Name = "Steve" };

            var postTask = client.PostAsJsonAsync<Student>("student", student);
            postTask.Wait();

            var result = postTask.Result;
            if (result.IsSuccessStatusCode)
            {

                var readTask = result.Content.ReadAsAsync<Student>();
                readTask.Wait();

                var insertedStudent = readTask.Result;

                Console.WriteLine("Student {0} inserted with id: {1}", insertedStudent.Name, insertedStudent.Id);
            }
            else
            {
                Console.WriteLine(result.StatusCode);
            }
        }
    }
}

The following table lists all the methods of HttpClient to send different HTTP requests.

Method Name Description
GetAsync Sends a GET request to the specified Uri as an asynchronous operation.
GetByteArrayAsync Sends a GET request to the specified Uri and returns the response body as a byte array in an asynchronous operation.
GetStreamAsync Sends a GET request to the specified Uri and returns the response body as a stream in an asynchronous operation.
GetStringAsync Sends a GET request to the specified Uri and returns the response body as a string in an asynchronous operation.
PostAsync Sends a POST request to the specified Uri as an asynchronous operation.
PostAsJsonAsync Sends a POST request as an asynchronous operation to the specified Uri with the given value serialized as JSON.
PostAsXmlAsync Sends a POST request as an asynchronous operation to the specified Uri with the given value serialized as XML.
PutAsync Sends a PUT request to the specified Uri as an asynchronous operation.
PutAsJsonAsync Sends a PUT request as an asynchronous operation to the specified Uri with the given value serialized as JSON.
PutAsXmlAsync Sends a PUT request as an asynchronous operation to the specified Uri with the given value serialized as XML.
DeleteAsync Sends a DELETE request to the specified Uri as an asynchronous operation.

Visit MSDN to know all the members of HttpClient and HttpClientExtension.