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COMP6325 Advanced Web Technologies

COMP6325 Advanced Web Technologies. Dr. Paul Walcott The University of the West Indies Session 6 – Building Enterprise-scale Web-based Applications – Part V : Web Services Spring 2009. Objectives. At the end of this session the student shall be able to: Describe a web service

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COMP6325 Advanced Web Technologies

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  1. COMP6325 Advanced Web Technologies Dr. Paul Walcott The University of the West Indies Session 6 – Building Enterprise-scale Web-based Applications – Part V : Web Services Spring 2009

  2. Objectives • At the end of this session the student shall be able to: • Describe a web service • Create a simple web service

  3. An ASP.NET application comprises of (MacDonald 2007, p. 130):

  4. Web services “Used primarily as a means for businesses to communicate with each other and with clients, Web services allow organizations to communicate data without intimate knowledge of each other's IT systems behind the firewall.” http://www.webopedia.com/TERM/W/Web_services.htm

  5. Web services cont’d • Web services use a variety of technologies (http://www.webopedia.com/TERM/W/Web_services.htm): • Extensible markup language (XML) – to describe the data • Simple object access protocol SOAP (SOAP) – to transport the data • Web Service definition language (WSDL) • Describes the capabilities of the Web Service • Universal description, discovery and integration (UDDI) – to list the available services • Hypertext Transfer Protocol (HTTP) – rules for transferring files over the Internet

  6. Creating a Web Service (Singh 2002) • As a simple example let us create a Calculator Web Service which: • Provides a description of the services offered • Multiplies two integers • Click here to get the two files required for our example: • Service.asmx (the web service) and • multiply.cs (our consumer)

  7. What is the first step when creating a Web Service? • Create a virtual directory that will be used to store your Web Service (Control Panel | Administrative Tools | Internet Information Services) • For our example call the virtual directory Calculator

  8. The Second step is to create the actual service that you want to provide • Our Web Service is stored in the file Service.asmx (the .asmx extension is used by Web Services): • The WebService page directive <%@ WebService language="C#" class="Calculator" %> defines the Web Service • The name space of the Web Service is specified using [WebService(Namespace="http://localhost/Calculator/")] • Each method provided by the Web Service begins with [WebMethod]

  9. The third step is to publish the service • Since we have already created a virtual directory and copied service.asmx into it, we have already published our service • To test our service simply type http://localhost/Calculator/Service.asmx • This returns a web page with a description of the services that are offered

  10. Supposed someone want to use our Calculator Service? • Anyone wanting to use our service will need to write a Web Service consumer, either: • A Web-based Service Consumer, or • A Windows Application-Based Web Service Consumer • For simplicity we will create a Windows Application-Based Web Service Consumer • Building a Web-based Service Consumer is also easy

  11. Next, we have to write proxy for the Web Service that is being consumed • The WSDL utility is used (at the command prompt) • WSDL http://localhost:8080/Calculator/service.asmx?WSDL • This creates a proxy (an intermediary between our application and the Web Service) • Calculator.cs is created which contains the proxy code • We now need to create a DLL for the proxy (Calculator.dll) • csc /target:library Calculator.cs

  12. What does the proxy do? • The proxy takes care of all the communication between our application and the Web Service • This includes the use of the SOAP and WSDL protocols

  13. Compiling the consumer • Now that the dll for the proxy has been created all that is left to be done is to compile the consumer with the proxy: • csc /reference:Calculator.dll multiply.cs

  14. Running the application • To run the newly created multiply application which utilises the calculator web service simply type: • > multiply 2 3 • The result returned is 2 * 3 = 6

  15. Conclusion • In this session • The term Web Service was defined • A simple Calculator Web service was created

  16. References Platt, D., “Introducing Microsoft .NET”, Third Edition, Microsoft Press, 2003 Ruvalcaba, Z., “Build Your Own ASP.NET Website Using C# And VB.NET, Chapter 1 – Introduction to .NET and ASP.NET”, 2004. Available online at http://www.sitepoint.com/print/asp-dot-net-introduction Ruvalcaba, Z., “Build Your Own ASP.NET Website Using C# And VB.NET, Chapter 2 – ASP.NET Basics”, 2004. Available online at http://www.sitepoint.com/print/asp-dot-net-basics Singh, S, “.NET Web Services Tutorial”, 2002. Available online at http://www.codeguru.com/Csharp/Csharp/cs_webservices/tutorials/article.php/c5477 W3Schools, “Web Services Tutorial”, nd. Available online at http://www.w3schools.com/webservices/default.asp

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