Introduction to WebServices

This article will explain you everything about Web Services in .Net, so lets get started with Web Service

What is Web Service?

• Web Service is an application that is designed to interact directly with other applications over the internet. In simple sense, Web Services are means for interacting with objects over the Internet.
  
• Web Service is
  
• Language Independent
• Protocol Independent
• Platform Independent
• It assumes a stateless service architecture.
• We will discuss more on web service as the article proceed. Before that lets understand bit on how web service comes into picture.

History of Web Service or How Web Service comes into existence?

• As i have mention before that Web Service is nothing but means for Interacting with objects over the Internet.
  
• 1. Initially Object - Oriented Language comes which allow us to interact with two object within same application.
• 2. Than comes Component Object Model (COM) which allows to interact two objects on the same computer, but in different applications.
• 3. Than comes Distributed Component Object Model (DCOM) which allows to interact two objects on different computers, but within same local network.
• 4. And finally the web services, which allows two object to interact internet. That is it allows to interact between two object on different computers and even not within same local network.

Example of Web Service

• Weather Reporting: You can use Weather Reporting web service to display weather information in your personal website.
• Stock Quote: You can display latest update of Share market with Stock Quote on your web site.
• News Headline: You can display latest news update by using News Headline Web Service in your website.
• In summary you can any use any web service which is available to use. You can make your own web service and let others use it. Example you can make Free SMS Sending Service with footer with your companies advertisement, so whosoever use this service indirectly advertise your company... You can apply your ideas in N no. of ways to take advantage of it.

Web Service Communication
Web Services communicate by using standard web protocols and data formats, such as

• HTTP
• XML
• SOAP

Advantages of Web Service Communication
Web Service messages are formatted as XML, a standard way for communication between two incompatible system. And this message is sent via HTTP, so that they can reach to any machine on the internet without being blocked by firewall.

Terms which are frequently used with web services

• What is SOAP?
• SOAP are remote function calls that invokes method and execute them on Remote machine and translate the object communication into XML format. In short, SOAP are way by which method calls are translate into XML format and sent via HTTP.

• What is WSDL?
• WSDL stands for Web Service Description Language, a standard by which a web service can tell clients what messages it accepts and which results it will return.
• WSDL contains every details regarding using web service
• Method and Properties provided by web service
• URLs from which those method can be accessed.
• Data Types used.
• Communication Protocol used.
  

• What is UDDI?
• UDDI allows you to find web services by connecting to a directory.

• What is Discovery or .Disco Files?
• Discovery files are used to group common services together on a web server.
• Discovery files .Disco and .VsDisco are XML based files that contains link in the form of URLs to resources that provides discovery information for a web service.
• .Disco File (static)
• .Disco File contains
• URL for the WSDL
• URL for the documentation
• URL to which SOAP messages should be sent.
  
• A static discovery file is an XML document that contains links to other resources that describe web services.
• .VsDisco File (dynamic)
• A dynamic discovery files are dynamic discovery document that are automatically generated by VS.Net during the development phase of a web service.

• What is difference between Disco and UDDI?
• Disco is Microsoft's Standard format for discovery documents which contains information about Web Services, while UDDI is a multi-vendor standard for discovery documents which contains information about Web Services.

• What is Web Service Discovery Tool (disco.exe) ?
• The Web Services Discovery Tool (disco.exe) can retrieve discovery information from a server that exposes a web service.

• What is Proxy Class?
• A proxy class is code that looks exactly like the class it meant to represent; however the proxy class doesn't contain any of the application logic. Instead, the proxy class contains marshalling and transport logic.
• A proxy class object allows a client to access a web service as if it were a local COM object.
• The Proxy must be on the computer that has the web application.
  

• What is Web Service Description Language Tool (wsdl.exe)?
• This tool can take a WSDL file and generate a corresponding proxy class that you can use to invoke the web service.
• Alternate of generating Proxy class through WSDL.exe is you can use web reference. Web Reference automatically generate a proxy classes for a web service by setting a web reference to point to the web service.
• Advantage of using Web Reference as compare to using WSDL.exe Tool is you can update changes done in web service class easily by updating web reference, which is more tedious task with WSDL.exe tool.

• Testing a Web Service?
• You can test web service without building an entire client application.
• With Asp.net you can simply run the application and test the method by entering valid input paramters.
• You can also use .Net Web Service Studio Tool comes from Microsoft.

Example of Creating Web Service in .Net

This Web Service will retrieve CustomerList Country Wise and return as dataset to client application for display.

Step1: Create a Web Service Application by File > New > Web Site > Asp.net Web Services
Named the web service, for example here i have choosen name "WSGetCustomerCountryWise"

Step2: Rename the default Service.asmx file to proper name, you also need to switch design view and change the class name with the same name you use to rename the service.asmx.
For example, "WSGetCustomerCountryWise.asmx" and switch to design view and change the class="Service" to class="WSGetCustomerCountryWise"

Step3: Rename the Service.CS File to proper name, you need to change the class name and constructor name too.
For example, "WSGetCustomerCountryWise.CS" and switch to code view and change the class and constructor name to "WSGetCustomerCountryWise"

After three steps your solution explorer looks as shown in figure




Step4: Create a Logic for Web Service

• Create a Method "GetCustomerCountryWise"
• Note: You need to specify [WebMethod] before method definition, if you want it to be accessible public, otherwise the method would not be accessible remotely.
• Specify proper argument and return type for method in web service.
• It is also good practise to specify the use "Description" attribute to tell what method is meant for.

For example, here i need to access data of northwind customers and want to return customer list country wise, so add namespace for

using System.Data;
using System.Data.SqlClient;
using System.Configuration;

[WebMethod(Description="It will generate Customer List, Country Wise")] public System.Xml.XmlElement GetCustomerCountryWise(string sCountry)
{
string sConn = ConfigurationManager.ConnectionStrings["connStr"].ToString();

string sSQL = "select CustomerId, CompanyName, ContactTitle, City " +
" from Customers where country = '" + sCountry + "'";

SqlConnection connCustomer = new SqlConnection(sConn);

DataSet dsCustomer = new DataSet();

SqlDataAdapter daCustomer = new SqlDataAdapter(sSQL, sConn);

daCustomer.Fill(dsCustomer,"Customers");

//Known bug while return "DataSet" is "Data source is an invalid type.
It must be either an IListSource, IEnumerable, or IDataSource."
//For more details on Error: http://support.microsoft.com/kb/317340

//So to access data we need to make use of XmlElement.

// Return the DataSet as an XmlElement.
System.Xml.XmlDataDocument xdd = new System.Xml.XmlDataDocument(dsCustomer);
System.Xml.XmlElement docElem = xdd.DocumentElement;
return docElem;
}

Step5: Build Web Service and Run the Web Service for testing by pressing F5 function key.






By pressing "Invoke" button will generate XML File.

So you are done creating web service application.

Example of Testing Web Service in .Net

This Web Service will display the information which had been retrieved from Remote computer by accessing public method "GetCustomerCountryWise".

Step1: Create a Test Web Site by File > New > Web Site > Asp.net Web Site
Named the web site, for example here i have choosen name "TestGetCustomerCountryWise"

Step2: Displaying data in gridview, so drag the gridview on to the form.

Step3: Right Click Solution Explorer and Choose "Add Web Reference"



Step4: Choose the option Web Service on the local machine or you can enter the .WSDL File address directly in URL space and press Go button.




Step5: Press "Add Reference button"


Step6: Writing Code for Displaying data in GridView
Here note: I have Pass "USA" as parameter in Country Field.

protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
//Create object of WSGetCustomerCountryWise Object
localhost.WSGetCustomerCountryWise objGetCustomerCountryWise
= new localhost.WSGetCustomerCountryWise();

DataSet dsCustomer = new DataSet();

// Get the data from Webservice.
XmlElement elem = objGetCustomerCountryWise.GetCustomerCountryWise("USA");

// Load the XML to the Typed DataSet that you want.
XmlNodeReader nodeReader = new XmlNodeReader(elem);
dsCustomer.ReadXml(nodeReader, XmlReadMode.Auto);

GridView1.DataSource = dsCustomer;

GridView1.DataBind();
}
}


Step7: Output as data displayed in GridView.




Few Facts about Web Service in .Net

• Each Response from web service is a new object, with a new state.
• Web Service are asynchronous because the request object from the client application and the response object from the web service are unique SOAP envelopes that do not require shared connection.
• This allow client application and the web service to continue processing while the interaction is ongoing.
• Instead of a user interface, it provides a standard defined interface called a contract.