What is httpcontext

https://docs.microsoft.com/en-us/dotnet/api/system.web.httpcontext?view=netframework-4.8

Encapsulates all HTTP-specific information about an individual HTTP request.

Remarks

Classes that inherit the IHttpModule and IHttpHandler interfaces are provided a reference to an HttpContext object for the current HTTP request.

The object provides access to the intrinsic固有的 Request, Response, and Server properties for the request.

This object is ready for garbage collection when the HttpRequest is completed. Its usage after the request completes could lead to undefined behavior, such as a NullReferenceException.

This object is only available in the thread controlled by ASP.NET. Usage in background threads could lead to undefined behavior.

HttpContext.Request

Gets the HttpRequest object for the current HTTP request.

The Request property provides programmatic access to the properties and methods of the HttpRequest class. Because ASP.NET pages contain a default reference to the System.Web namespace (which contains the HttpContext class), you can reference the members of HttpRequest on an .aspx page without using the fully qualified class reference to HttpContext. For example, you can use Request.Browser to get the capabilities of the client browser. However, if you want to use the members of HttpRequest from an ASP.NET code-behind module, you must include a reference to the System.Web namespace in the module and a fully qualified reference to both the currently active request/response context and the class in System.Web that you want to use. For example, in a code-behind page you must specify the fully qualified name HttpContext.Current.Request.Browser.

Note

ASP.NET will throw an exception if you try to use this property when the HttpRequest object is not available. For example, this would be true in the Application_Start method of the Global.asax file, or in a method that is called from the Application_Start method. At that time no HTTP request has been created yet.

HttpContext.Response

The Response property provides programmatic access to the properties and methods of the HttpResponse class. Because ASP.NET pages contain a default reference to the System.Web namespace (which contains the HttpContext class), you can reference the members of HttpContext on an .aspx page without using the fully qualified class reference to HttpContext.

For example, you can use Response.Write("some output") to write output to an HTTP output stream.

However, if you want to use the members of HttpResponse from an ASP.NET code-behind module, you must include a reference to the System.Web namespace in the module and a fully qualified reference to the currently active request/response context and the class in System.Web that you want to use. For example, in a code-behind page you must specify the fully qualified name HttpContext.Current.Response.Write("some output").

HttpContext Object for Developers

HttpContext object will hold information about the current http request.

In detail, HttpContext object will be constructed newly for every request given to an ASP.Net application and this object will hold current request specific informations like Request, Response, Server, Session, Cache, User and etc.

For every request, a new HttpContext object will be created which the ASP.Net runtime will use during the request processing.

A new HttpContext object will be created at the beginning of a request and destroyed when the request is completed.

To know more about the use of HttpContext object in ASP.Net request processing please follow the article attached in the reference section of this article.

Also, this object can be very well used in our application to solve some of problems which I will discuss in this article.

One of the best features of HttpContext object is using its Item Collection. This article will contemplate on some of the very useful features that can be achieved through HttpContext Class.

Hide QueryString or Pass value with Server.Transfer()

Sometimes, we will have requirements where we need to pass data from source form to destination form when using Server.Transfer() method.

Since, Server.Transfer will make no round trip to the client, the destination page processing will also falls under the same request.

This is one of the ideal scenario where we can use the Item collection of HttpContext object. Refer the below code where we are passing EmployeeID from one form to another.

Source Form

Context.Items.Add("empID", "123456");

Server.Transfer("Destination.aspx");

Destination Form

string empID = Context.Items["empID"].ToString();

Response.Write(empID);

Accessing Request/Response/Server/Session/Cache/User object in a Class

Most of us think the above objects can be accessed only in CodeBehind file and it can’t be accessed outside codebehind class i.e. any other custom class. But in reality, it can be accessed via the current request’s HttpContext object.

How to get the HttpContext object of the current request in a class file?

HttpContext class has a static property called Current which gives us the reference of current request’s HttpContext object. Once we have the HttpContext object we can access those objects easily.

public class AccessPageObjects

{

       public AccessPageObjects()

       {

              //

              // TODO: Add constructor logic here

              //

       }

    public void Print()

    {

        HttpContext context = HttpContext.Current;

        context.Response.Write("Test");

        context.Session["Key"] = "Value";

        string user = context.User.Identity.Name;     

    }

}

For the above code to work we need to make sure that we are including System.Web namespace in the class file.

Pass value to usercontrols using HttpContext object

We can pass values to usercontrols from codebehind using Context.Item Collection.

UserControl

public partial class WebUserControl : System.Web.UI.UserControl

{

protected void Page_Load(object sender, EventArgs e)

{

Employee emp = Context.Items["emp"] as Employee;

Response.Write(emp.FirstName + " " + emp.LastName + " in user control.");

}

}

The above requirement can also be achieved through Page.Item collections in the same way like above. But Context object will be really useful when we need to pass an object from a source page to destination page’s usercontrols.

Source Form

Employee emp = new Employee();

emp.FirstName = "Satheesh";

emp.LastName = "Babu";

Context.Items.Add("emp", emp);

Server.Transfer("Destination.aspx");

UserControl in Destination Page

public partial class WebUserControl : System.Web.UI.UserControl

{

protected void Page_Load(object sender, EventArgs e)

{

Employee emp = Context.Items["emp"] as Employee;

Response.Write(emp.FirstName + " " + emp.LastName + " in user control.");

}

}

ASP.Net Request Processing Time

A very good use of HttpContext object will be calculating the request processing time. Take a look at Rick’s article in West-Wind with the title “A low-level Look at the ASP.NET Architecture” where he explains it very neatly. Find the link in the reference section for a depth understanding in ASP.Net request processing. Request processing time can be calculated in Global.asax file through Application_BeginRequest and Application_EndRequest event. By default, this event will not be present in Global.asax file so we need to add it explicitly.

protected void Application_BeginRequest(Object sender, EventArgs e)

{

Context.Items.Add("Request_Start_Time", DateTime.Now);

}

protected void Application_EndRequest(Object sender, EventArgs e)

{

TimeSpan tsDuration = DateTime.Now.Subtract((DateTime)Context.Items["Request_Start_Time"]);

}

Conclusion

This article will help developers to understand the usage of HttpContext object at one place to achieve some of the handy things. Most of the tips discussed here use Item collection in the Context object to accomplish the tasks and this proves the importance of Item collection packed with HttpContext object. Thus, we can understand that HttpContext object is not only used by the ASP.Net runtime for request processing but also by developers.

Happy Coding!!