Consuming Web Services

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Consuming Web Services

• MIST4630

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What are Web Services

• A web service is a piece of business logic,
  located somewhere on the Internet, that is
  accessible through standard-based Internet
  protocols such as HTTP, or SMTP. Using a web
  service could be as simple as logging into a site
  or as complex as facilitating a
  multi-organization business negotiation.
  (Chappell Jewell, Java Web Services, 2002)

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According to W3Schools

• Web services are units of code located on some
  server on the Internet
• Web services are designed to work with
  third-party code
• Described using a service description language
• Web services use XML based communicating
  protocols
• Web services are independent of operating systems
  
• Web services are independent of programming
  languages
• Web services connect people, systems and devices

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Benefits of Web Services

• Easier to communicate between applications
• Easier to reuse existing services
• Easier to distribute information to more
  consumers
• Rapid development
• Web services make it easier to communicate
  between different applications. They also make it
  possible for developers to reuse existing web
  services instead of writing new ones.
• Web services can create new possibilities for
  many businesses because it provides an easy way
  to distribute information to a large number of
  consumers. One example could be flight schedules
  and ticket reservation systems.

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Major Web Services Technologies

• HTTP
• XML
• SOAP Simple Object Access Protocol
• SOAP some say Service-Oriented Architecture
  Protocol
• WSDL Web Service Description Language
• UDDI Universal Description, Discovery, and
  Integration

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XML Web Services Infrastructure
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Resources

• Read introduction and case studies on the
  following web sites
• http//www-306.ibm.com/software/solutions/webservi
  ces/overview.html
• http//www.w3schools.com/wsdl/wsdl_uddi.asp
• www.uddi.org

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Steps for Consuming Web Services

• Service discovery locate the WSDL contract for
  the desired web service
• Make the service local create a Proxy Class, a
  .vb class file
• Compile the proxy class create a .dll assembly
  and put it in the library
• Create a new instance of the proxy class in the
  client application and call the desired methods

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Step 1. Discovering

• Two methods using UDDI or search engine
• UDDI
• Webservice register directories
  (http//www.uddi.com)
• Provide URL for the applications WSDL file
• Using search engine
• Currently, UDDI is in its infancy and you might
  just as well find a web service using a search
  engine such as Google.
• http//www.webserviceX.NET
• http//www.capescience.com/webservices

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Step 2. Create a Proxy Class

• Create a Proxy Class to communicate with the web
  service resulting a .vb class file
• Command line
• wsdl /lvb /outfilename.vb http//domain/folder/f
  ilename.asmx?wsdl

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Step 3. Compile the Proxy Class

• Compile the proxy class resulting a .dll
  assembly put it in a /bin folder
• Command line
• Vbc /tlibrary /rSystem.Web.dll,System.dll,System
  .Web.Services.dll,System.Xml.dll,System.Data.dll
  /outbin\filename.dll filename.vb

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Step 2,3. Create Proxy Class in Web Matrix

• ToolsWebService Proxy Generator

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Prelude of Using the Proxy Class

• Investigate the .vb file and get the information
  about class name, methods, and parameters

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Step 4. Use the Proxy Class

• Use the class in the same manner as you would use
  a .NET provided class (e.g., an arraylist, or a
  datarow)
• Import the namespace to your application
• Instantiate a class object
• Call the methods