What is content negotiation in ASP.Net Web API?

 Content negotiation is basically a process of selecting the best representation from multiple representations that are available for a given response.

 It simply allows one to choose rather than negotiate content that one wants to get in response. It is performed at the server-side. In simple words, 

it chooses the best media type for matters to return a response to an incoming request.

There are two types of headers available for content negotiation:

• Content-Type: This header tells the server about the information that it will receive from the client.
• Accept: This header shows the data format requested by the client from the server.

We know that there are three pillars of the internet, they are:

• The resource
• The URL
• The representation

The formal definition of Content Negotiation is “the process of selecting the best representation for a given response when there are multiple representations available”.

By checking the “Accept” header, the Web API understands which representation the client is able to accept. For example, if we specify that the client can understand the following representation:

 

application/xml , application/json, text/javascript

What are the main return types supported in ASP. Net Web API?

 It supports the following return types:

HttpResponseMessage

IHttpActionResult

Void

Other types such as string, int, etc

How to register an exception filter globally?

 One can register exception filter globally using following code:

Web API global filters are registered through the HttpConfiguration object available to you in the Register method WebApiConfig.cs if you're using a project template with WebActivator:

public static void Register(HttpConfiguration config)
{
    //stuff before
    config.Filters.Add(new MyWebApiFilter());
    //stuff after
}

or otherwise in the global.asax.cs:

GlobalConfiguration.Configuration.Filters.Add(new MyWebApiFilter());

How to handle errors in Web API?

 One can use HttpResponseException, HttpError, Exception filters, register exception filters, Exception handlers to handle errors. Exception filter can be used to identify unhandled exceptions on actions or controllers, exception handlers can be used to identify any type of unhandled exception application-wide, and HttpResponseException can be used when there is the possibility of an exception.

Explain media type formatters.

 In web API, media type formatters are classes that are responsible for serialization data.

Web API can understand request data format in a better way and send data in a format that the client expects. It simply specifies data that is being transferred among client and server in HTTP response or request. 

JsonMediaTypeFormatter ->application/json, text/json

XmlMediaTypeFormatter ->application/xml, text/json

 

What Is an Idempotent API? How to handle multiple request in web API.

Consuming ASP.NET Web API REST Service In ASP.NET MVC Using HttpClient

 Steps to Consume Web API in MVC.

Step1: Install HTTP Client library from NuGet.

What is HttpClient?

HttpClient is base class which is responsible to send HTTP request and receive HTTP response resources i.e from REST services.

Step2:Install WebAPI.Client library from NuGet

Step3: Add Model and Controller class.

Step4: 

Our hosted Web API REST Service includes these two methods, as given below.

GetAllEmployees (GET )

GetEmployeeById (POST ) which takes id as input parameter

We are going to call GetAllEmployees method which returns the all employee details ,The hosted web api REST service base URL is http://192.168.95.1:5555/ and to call GetAllEmployees from hosted web API REST service, The URL should be Base url+api+apicontroller name +web api method name as following,

http://192.168.95.1:5555/api/Employee/GetAllEmployees

In the preceding url

http://localhost:56290 Is the base address of web API service, It can be different as per your server.

api It is the used to differentiate between Web API controller and MVC controller request .

Employee This is the Web API controller name.

GetAllEmployees This is the Web API method which returns the all employee list.

using ConsumingWebAapiRESTinMVC.Models;
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;
using System.Web.Mvc;

namespace ConsumingWebAapiRESTinMVC.Controllers
{
    public class HomeController : Controller
    {
        //Hosted web API REST Service base url
        string Baseurl = "http://192.168.95.1:5555/";
        public async Task<ActionResult> Index()
        {
            List<Employee> EmpInfo = new List<Employee>();
            using (var client = new HttpClient())
            {
                //Passing service base url
                client.BaseAddress = new Uri(Baseurl);
                client.DefaultRequestHeaders.Clear();
                //Define request data format
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                //Sending request to find web api REST service resource GetAllEmployees using HttpClient
                HttpResponseMessage Res = await client.GetAsync("api/Employee/GetAllEmployees");
                //Checking the response is successful or not which is sent using HttpClient
                if (Res.IsSuccessStatusCode)
                {
                    //Storing the response details recieved from web api
                    var EmpResponse = Res.Content.ReadAsStringAsync().Result;
                    //Deserializing the response recieved from web api and storing into the Employee list
                    EmpInfo = JsonConvert.DeserializeObject<List<Employee>>(EmpResponse);
                }
                //returning the employee list to view
                return View(EmpInfo);
            }
        }
    }
}

C#