Creating and Consuming a Web Service

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Creating and Consuming aWeb Service
MIS426 ASP.NET M. Featherman Washington State
University
http//dotnet.cbe.wsu.edu/featherman/ MoneyConver
ter/WebForm1.aspx
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Whats the big deal about Web Services??

• They allow developers to share their work, and
  bring together disparate info systems (regardless
  of development language, and machine host type)
• Any old code can be rolled into a web-service and
  consumed by others
• Allow code to be consumed with or without user
  intervention (machine can call code in effect
  ask for help/outsource - on its own)
• A way around the proprietary mess as they use XML
  (to format the requests and responses) and HTTP
• .NET makes this all incredibly easy

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An Example - Overview

• A webservice .asmx file has been created and sits
  on the edu.wsu.cbe.dotnet server
• It converts between dollars and euros
• It can be referenced/called by any .aspx page
• The client .aspx page
• Works with a proxy (referenced copy) of the
  webservice
• Feeds the webservice values that are used as
  function arguments
• Instantiates the web service and makes the
  function calls and
• displays the results

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Overview

• In effect we are calling a function in a class
  that someone else wrote
• The code exists on someone elses server
• We can consume their code to get a project
  completed more quickly
• We dont have to know how to perform the
  calculation, just what arguments to feed it and
  how to handle the return value
• Web services are often provided for a fee

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Agenda

• We will now look at the web service's code
• Create a new .aspx project
• Add a web reference to the .asmx (web service)
  file
• Use the VS IDE to prep the UI
• Write the code in the aspx file
• Run the project
• Look at the glossary of terms

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Converter.asmx has 3 functions in a class called
Converter

• Function EuroToDollar this accepts a euro
  amount and returns the equivalent dollars they
  are worth
• Function DollarToEuro - this accepts a dollar
  amount and returns the equivalent euros they are
  worth
• Private Function GetEuroToDollarConversionRate
  an internal function that mimics a table lookup
  to provide the up-to-date conversion rate

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A Web Service has been Createdhttp//dotnet.cbe.w
su.edu/featherman/Converter/Converter.asmx

• ltWeb Service(Description"A web service for
  converting currencies", _
• Namespace"http//tempuri.org/")gt _
• Public Class Converter this class will be
  consumed in the .aspx file
• Inherits System.Web.Services.WebService
• ltWebMethod(Description"Convert from Euro to US
  Dollar currency")gt _
• Function EuroToDollar(ByVal amount As
  Decimal) As Decimal
• Return amount GetEuroToDollarConversionR
  ate()
• End Function

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Converter.asmx (Cont)

• ltWebMethod(Description"Convert from US Dollar
  to Euro currency")gt _
• Function DollarToEuro(ByVal amount As
  Decimal) As Decimal
• Return amount / GetEuroToDollarConversionR
  ate()
• End Function
• Private Function GetEuroToDollarConversionRate
  () As Decimal
• 'a real app would read this from an
  array or database
• Return 0.9
• End Function

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Now make the .aspx page that references and
utilizes it
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Add the WebReference

• In the solution explorer, right-click references
  and choose add web reference then paste in the
  URL
• http//dotnet.cbe.wsu.edu/featherman/Converter/Co
  nverter.asmx
• Click OK and a reference to the webservice will
  be added

This is where the WebService lives
Heres its code
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Write .ASPX code that uses the web-service class

• Private Sub btnToEuros_Click(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles btnToEuros.Click
• 'create the proxy
• Dim conv As New edu.wsu.cbe.dotnet.Convert
  er()
• 'get the argument that will be passed
  into the method of the webservice (amount)
• Dim decValue As Decimal
  CDec(txtDollars.Text)
• 'call the remote method of the webservice
• Dim decResult As Decimal
  conv.DollarToEuro(decValue)
• 'display the result of the calculation
• Me.txtEuros.Text FormatNumber(decResult.
  ToString, 2)
• End Sub

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Write .ASPX code that uses the web-service class

• Private Sub btnToDollars_Click(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles btnToDollars.Click
• Dim conv As New edu.wsu.cbe.dotnet.Converter()
• Dim decValue As Decimal CDec(txtEuros.Text)
• Dim decResult As Decimal conv.EuroToDollar(decV
  alue)
• Me.txtDollars.Text FormatCurrency(decResult.ToS
  tring, 2)
• End Sub

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Success!!
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Glossary Web-Service

• Discrete units of programmatic functionality
  (code w/functions) exposed to clients
  (.aspx/.ascx or windows projects) via
  standardized communications protocols (HTTP) and
  data formats (XML)

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Glossary UDDI Advertising web services

• UDDI Universal Description, Discovery and
  Integration a multi-vendor initiative designed
  to provide an web-based business registry so that
  creators of web services may register their
  publicly available web services
• a standard way to expose info about (and sell)
  available web-services (codified functionality)

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Glossary WSDL - Describing to consumers what
the web service can do

• WSDL Web service description language an
  XML-based standard for docs that describe the
  services exposed by the web service (assembly
  metadata)
• Used to describe the publicly available methods,
  parameters, datatypes and return value datatype
• Every web service registered with a UDDI registry
  needs this info called its WSDL contract

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Glossary - SOAP - How do we exchange info between
the web service and client calling it?

• Using a protocol called SOAP Simple object
  Access Protocol A lightweight protocol
  XML-based messaging protocol for exchange of info
  in a decentralized, distributed environment
• Provides a framework for formatting the - SOAP
  messages (called envelopes) and how to process
  them
• Has data encoding, and request/response
  processing standards