Basics Of ASP.NET Web Services For New Developers
Introduction:
1. A Web Service is an entity or a piece of code which is hosted on the
Web, which serves a specific
purpose.
2. A Web
Service is a part of a software
application which is hosted on the Web and which does a particular function in
order to execute the business logic.
3. A Web Service allows a website to interact with other websites
irrespective of the programming language the web site's been written in and also irrespective of the hardware
& OS concerns of the machines.
example
• Suppose, you are a developer and you have some 3 different
mathematical websites under you, demanded by various clients. A common functionality
needs to be implemented in all the 3 websites, lets say displaying a Fibonacci series in a text area.
• The
question which arises
here is, are you going
to write separate piece
of codes to have the same functionality 3 times. Well it would be a redundant extra effort, if you would try
to aim at this approach.
Here, the need for a Web Service comes into picture.
Code the functionality of displaying a Fibonacci series in a Web Service just once, and call this web service in the 3 different web sites. There you go, you are done. You need not write the same code thrice or else.
Lets start with the creation of the Web Service. (in .NET
3.5)
1) Open Visual Studio 2008 Client. Click on New>Web Site
>ASP.NET Web Service. Give the path where you want to place the code. Refer
to the below screenshots.
2) Visual Studio
will open a default Service.cs file in which you can write your
methods. Write the below lines of code.
using System;
using System.Collections.Generic;
using System.Web;
using System.Web.Services;
[WebService(Namespace=
"http://tempuri.org/")]
[WebServiceBinding(ConformsTo=
WsiProfiles.BasicProfile1_1)]
// To allow this
Web Service to be called from script, using ASP.NET AJAX, uncomment the
following line.
// [System.Web.Script.Services.ScriptService]
public class Service : System.Web.Services.WebService
{
public Service ()
{
//Uncomment the
following line if using designed components
//InitializeComponent();
}
[WebMethod]
public int Area(int l, int b)
{
return l * b;
}
[WebMethod]
public int Perimeter(int l, int b)
{
return 2 * (l +b);
}
}
3) Build the
solution and view the Service.asmx file in the browser. It will be something
like below:
4) The Web Methods created will be evident and will be
invoked via HTTP POST method if the links Area and Perimeter are clicked.
•So here it is, a very
basic Web Service has been coded and
created, which will help us to calculate the area and perimeter of a rectangle.
•You might want copy the Web Service
URL because they are used later in the article.
•Next, we will see how
to call and use the Web Service in times of need.
•Well, there may be 3
methods by which a Web Service is called, depending upon the scenarios.
1) By HTTP POST method.
2) By creating a Proxy Class
3) By using XMLHTTP Request object
over SOAP
Let's discuss each of them
in brief:
---------------------------------------------------------------------------------------------
1) HTTP POST method: This method can be
used directly by calling the .asmx file from the client.
The most favorable method to execute an HTTP POST method
is to have the codes inside an HTML file. Let’s get started to implement it.
Open your notepad and
write the below lines of code in it:
<html>
<head>
<title>Web Service Call using HTTP POST</title>
<body>
<form action="http://localhost:43529/WebService/Service.asmx/Area"
method="POST">
<input
name="l">
<input
name="b">
<input
type="submit" value="Click for Area">
</form>
<form action="http://localhost:43529/WebService/Service.asmx/Perimeter"
method="POST">
<input name="l">
<input name="b">
<input type="submit" value="Click for Perimeter">
</form>
</body>
</head>
</html>
v Just a friendly
reminder, you would want
change the Web
Service URL in the above code, by your own URL, which you would have copied
sometime earlier..
v When the button
“Click for Area” or “Click for Perimeter” is clicked, we would see that the
specific methods of the Web
Service are called and the
result is in the form of an XML.
v One of the
limitations of HTTP POST method can be thought as of: We are unable to build
Web Methods which take complex types as parameter or return values.
------------------------------------------------------------------------------------------------------------
2) Creation
of a Proxy Class:
This method is widely used by developers. This method actually makes use of the
full potential of a Web Service.
Let’s implement this and see its wonders.
•We need to create one
ASP.NET website to see and implement this method.
•Open Visual Studio
once again and click on New>Website>ASP.NET Website. Give the path where
you want to place the code.
This web site creation will open a Default.aspx page,
its aspx.cs page, an App_Code folder and few more
stuffs.
Open the Default.aspx page and design it as per below
screenshot:
It’s basically 4 ASP label controls, 4 ASP text box
controls and 1 ASP button bound under 1 div.
v Now the most
important aspect of this very method comes into play. Addition of the
previously created Web Service.
Ø Right-click the
project and click on “Add Web Reference”. The click will open a dialog box
similar to the below screenshot.
v Now, we need to catch
the Web Service here either by adding the URL or by browsing through the
various options given. Successful addition of the Web Service will yield “Web
services found at this URL”. You would see the methods that you have actually
created. You might want to change the name of the web reference from “localhost” to something else
to avoid confusion and stuffs. Click on Add Reference and there you go. You
have successfully added a Web Reference to your ASP.NET website.
The solution explorer will be something like below:
v Now, once the Web
Reference is added, let’s write some code in Code-Behind to make use of the web
service.
v Open Default.aspx.cs file and on
Button Click event, add the following code:
using System;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
public partialclass_Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void btnClick_Click(object sender, EventArgs e)
{
if (!string.IsNullOrEmpty(txtLength.Text) && !string.IsNullOrEmpty(txtBreadth.Text))
{
Maths.Service obj =
new Maths.Service();
int l = Convert.ToInt32(txtLength.Text);
int b = Convert.ToInt32(txtBreadth.Text);
txtArea.Text = Convert.ToString(obj.Area(l, b));
txtPerimeter.Text = Convert.ToString(obj.Perimeter(l, b));
}
}
}
Now, let me explain
the above code further. The bold line of code is what this method is all about,
Creation of proxy class.
We are making an
object of the Web Service added and then are using that object to call the
individual methods of the Web Service. Rest of the code is self-explanatory,
which will calculate the area and perimeter of the rectangle.
Build the solution
and view the Default.aspx file in the browser.
Enter some values for
length and breadth and click on the button.
You will see the area
and perimeter displayed in the placed text-boxes.
------------------------------------------------------------------------------------------------------------
3) By
using XMLHTTP Request object over SOAP:
First let’s see what
SOAP is.
SOAP (Simple Object
Access Protocol) is a protocol used for messaging and is completely XML based.
SOAP provides a
complete set of rules for messages and also, rules for entities like message
encoding, message handling etc.
Syntax of a SOAP
message will be as follows:
<?xml
version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Body>
</soap:Body>
</soap:Envelope>
A SOAP message is
called an Envelope, which further has Header and Body tags.
Header tag is
optional whereas Body tag is mandatory to use in order to submit a message.
vNow,
let’s see what exactly XMLHttpRequest is.
•The XMLHttpRequest specification
defines an API that provides scripted client functionality for transferring
data between a client and a server.
It is used to
send HTTP or HTTPS requests
directly to a web server and load the
server response data directly back into the script.
