Basics of
ASP.NET Web Services
Hi Guys!! In
this article, I am going to explain you the basic concepts of ASP.NET Web
Services.
Introduction:
We can now use
ASP.NET to create Web Services based on industrial standards including XML, SOAP
and WSDL.
A Web Service
is a software program that uses XML to exchange information with other software
via common internet protocols. In a simple sense, Web Services are a way for
interacting with objects over the Internet.
A web service
is…
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Language Independent.
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Protocol Independent.
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Platform Independent.
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It assumes stateless service architecture.
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Scalable (e.g. multiplying two numbers together to an
entire customer-relationship management system).
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Programmable (encapsulates a task).
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Based on XML (open, text-based standard).
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Self-describing (metadata for access and use).
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Discoverable (search and locate in registries)- ability of
applications and developers to search for and locate desired Web services
through registries. This is based on UDDI.
Web Service
History:
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Microsoft
coined the term "Web services" in June 2000, when the company introduced Web
services as a key component of its .Net initiative, a broad new vision for
embracing the Internet in the development, engineering and use of software.
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As others
began to investigate Web services, it became clear that the technology could
revolutionize (be the next stage in) distributed computing.
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Web services
encompass a set of related standards that can enable any two computers to
communicate and exchange data via a network, such as the Internet.
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The primary
standard used in Web services is the Extensible Markup Language (XML) developed
by the World Wide Web Consortium (W3C).
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Developers use
XML tags to describe individual pieces of data, forming XML documents, which are
text-based and can be processed on any platform.
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XML provides
the foundation for many core Web services standards (SOAP, WSDL, and UDDI) and
vocabularies (XML-based markup for a specific industry or purpose).
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Almost every
type of business can benefit from Web services such as expediting software
development, integrating applications and databases, and automating transactions
with suppliers, partners, and clients.
Key Web
Service Technologies:
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XML- Describes only data. So,
any application that understands XML-regardless of the application's programming
language or platform-has the ability to format XML in a variety of ways
(well-formed or valid).
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SOAP- Provides a
communication mechanism between services and applications.
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WSDL- Offers a
uniform method of describing web services to other programs.
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UDDI- Enables the
creation of searchable Web services registries.
When these
technologies are deployed together, they allow developers to package
applications as services and publish those services on a network.
Web services
advantages:
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Use open,
text-based standards, which enable components written in various languages and
for different platforms to communicate.
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Promote a
modular approach to programming, so multiple organizations can communicate with
the same Web service.
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Comparatively
easy and inexpensive to implement, because they employ an existing
infrastructure and because most applications can be repackaged as Web services.
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Significantly
reduce the costs of enterprise application (EAI) integration and B2B
communications.
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Implemented
incrementally, rather than all at once this lessens the cost and reduces the
organizational disruption from an abrupt switch in technologies.
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The Web
Services Interoperability Organization (WS-I) consisting of over 100 vendors
promotes interoperability.
Web Services
Limitations:
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SOAP, WSDL,
UDDI- require further development.
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Interoperability.
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Royalty fees.
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Too slow for
use in high-performance situations.
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Increase
traffic on networks.
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The lack of
security standards for Web services.
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The standard
procedure for describing the quality (i.e. levels of performance, reliability,
security etc.) of particular Web services –management of Web services.
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The standards
that drive Web services are still in draft form (always will be in refinement).
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Some vendors
want to retain their intellectual property rights to certain Web services
standards.
Web Service
Example:
A web service
can perform almost any kind of task.
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Web Portal-
A web portal
might obtain top news headlines from an Associated press web service.
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Weather
Reporting- You can use
Weather Reporting web service to display weather information in your personal
website.
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Stock
Quote- You can display
latest update of Share market with Stock Quote on your web site.
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News
Headline: You can display
latest news update by using News Headline Web Service in your website.
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You can make
your own web service and let others use it. For example you can make Free SMS
Sending Service with footer with your company’s advertisement, so whosoever uses
this service indirectly advertises your company. You can apply your ideas in N
no. of ways to take advantage of it.
Example of
Creating Web Service in .Net:
Here are
samples codes which I use to create and consume ASP.NET Web Service:
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Step 1- Create the ASP.NET Web Service Source File:
Open Visual
Studio 2010 and create a new web site.
->Select .Net Framework 3.5. ->Select ASP.NET Web Service page -> then, you
have to give the name of your service. In this example I am giving it's name "mywebservice".
Then Click the ok Button. A screen-shot of this activity is given below.
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Step 2- click on the
"ok" button; you will see the following window.
Here (in the
above figure), you will note that there is predefined method "HelloWorld"
which returns the string "Hello World". You can use your own method and
can perform various operations. Here I made a simple method which returns the
multiplication of two numbers using the code.
Service.cs:
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using
System;
using System.Collections.Generic;
using System.Linq;
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
{
[WebMethod]
public int
Multiplication(int a,int
b)
{
return (a*b);
}
}
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Before Debugging the above Web Service see some important term:
using
System.Web.Services;
This directive
allows you to refer to objects in the ‘System.Web.Services’
namespace without having to fully qualify the request. This statement is
optional, but if it is not included, every reference to an object in this
namespace must be fully qualified. An example is the next line, which is our
class declaration. With the using statement, it looks as follows in C#:
The [WebMethod] attribute:
The
Service class exposes a single method, the
public method Multiplication, which takes two integer arguments and
returns the multiplication of two number as integer. To expose a method as a
part of a web service, you must decorate it with the WebMethod attribute, which
tells the compiler to treat it as such. Any method marked with the WebMethod
attribute must be defined as public. Class methods exposed as web services
follow the same object-oriented rules as any other class, and therefore methods
marked private, protected, or internal are not accessible and will return an
error if you attempt to expose them using the WebMethod attribute.
In the
Solution Explorer you will see…
Service.asmx-
which contains
the following code:
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<%@
WebService Language="C#"
CodeBehind="~/App_Code/Service.cs"
Class="Service"
%>
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The page
directive
WebService is required and
the class is the name of the .NET Class to expose the Web Service, each method
exposes as Web Service Class Method need to have a declarative attribute
statement.
The WebService
directive is similar to the Page directive that begins most .aspx pages. For the
Multiplication web service to work, you must assign values to two
WebService directive attributes: Language and Class.
The required
Language attribute lets .NET know which programming language the class has been
written in. As you might guess, the acceptable values for the language attribute
are currently C#, VB, and JS for JScript.NET.
The Class
attribute, also required, tells ASP.NET the name of the class to expose as a web
service. Because a web service application can comprise multiple classes, some
of which may not be web services, you must tell .NET which class to expose, a
step analogous to declaring a Main() method to indicate the entry point of a
.NET console application or component. Note that even if your web service
contains only one class, setting this attribute is required.
Now back to
our web service.
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Step 3- Build Web
Service and Run the Web Service for testing by pressing F5 function key.
Copy the URL
of this web service for further use.
Click on the
Multiplication button to test the web service.
Enter the
value of ‘a’ and ‘b’.
By pressing
the "Invoke" button a XML file is generated.
Now our web
service is ready to use; we just need to create a new web site to consume the
web service.
Example of
Testing Web Service in .Net:
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Step 5-
Create a
Test Web Site by File > New > Web Site >
Asp.net Web Site
Name the web
site, for example here I have chosen the name "Test".
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Step 6- Right-click
Solution Explorer and choose "Add Web Reference".
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Step 7-
Paste the
URL of the web service and click on 'Go' button and then 'Add reference'.
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Step 8- Now your web
service is ready to use in the Solution Explorer you will see.
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Step 9- Go to the
design of the Default.aspx page; drag
and drop three Textboxes and one button.
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Step 10-
Go
to Default.cs page and on the button
click event use the following code.
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protected void
Button1_Click(object sender,
EventArgs e)
{
localhost.Service mys
= new localhost.Service();
// you need to create the object of the web service
int a =
Convert.ToInt32(TextBox1.Text);
int b =
Convert.ToInt32(TextBox2.Text);
int c =
mys.Multiplication(a, b);
TextBox3.Text = c.ToString();
}
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Step 11- After pressing
the F5 function key to run the website, you will see:
Enter the
number.
Press the show
button.
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