Web Services

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Web Services
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What are they?

• Web services are a platform independent way to
  exchange data using XML. They are components of
  business logic that can be accessed over the
  Internet. They are a way of re-using someone
  elses logic without re-creating it yourself.

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Examples

• An e-commerce company can use a shippers web
  service to calculate the exact cost of a
  shipment.
• National weather forecasters use them to supply
  data to web-sites and news organizations.
• Stock prices are provided this way by major
  exchanges and corporations.

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Benefits of Web Services

• Simple easily supported on many platforms
• Loosely Coupled the interface can be extended
  and new methods added without affecting clients
  as long as old methods and parameters are still
  provided
• Stateless a request is made, then result is
  returned and the connection closes, no permanent
  connection
• Firewall Friendly uses HTTP, not usually blocked

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When to use Web Services

• Cross platform i.e. Communicate between a Java
  app and a .NET app
• Cross trust boundaries between two unrelated
  organizations
• Future considerations if there is a possibility
  that the logic may have to support third party
  integration

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When to Avoid Web Services

• .Net to .Net there are better ways to
  communicate between servers, such as .NET
  remoting
• .Net Apps rather than provide a Service, if two
  apps need the same logic create a class library
  assembly compiled to a DLL, which is then used in
  both apps.

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Discovering and Using Services

• Right click your project in Solution Explorer
• Select Add Web Reference
• In the page that appears input the URL of a web
  service (.asmx or .wsdl file)
• When the service is found a listing will appear
  of all the available methods and a link to
  Service Description this is where you find out
  how the service works
• Select Add Reference and VS2008 will add all the
  necessary files to your solution

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Proxy Class

• A Web Service communicates with a subscriber
  using XML and SOAP (Simple Object Access
  Protocol). .NET manages these protocols for you
  by generating the SOAP message and transmitting
  it using HTTP. The response is then converted
  back to the corresponding .NET type.
• SOAP Tutorial

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Coding Limitations

• You can create your web service using any valid
  .NET code. However there is no interface design
  because the service is stateless. Parameter and
  return types are limited to the XML Schema
  standard such as strings and numbers. You can not
  pass proprietary .NET objects such as FileStream
  or an Event Log.

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Web Service Data Types

• Simple types int, unsigned int, float, double,
  decimal, bool, string, char, byte, DateTime
• Arrays of any supported type, ArrayList, byte
  arrays (which will automatically be Base64
  encoded)
• DataSet and DataTable, but not DataColumns or
  DataRows

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Creating a Web Service

• Choose Add New Item form the context menu of a
  folder
• Select Web Service and name the file
• The asmx file is created in the folder, this file
  is not modified by you as there can be no user
  interface
• Another file, asmx.cs is created in your App_Code
  folder. This is where your code is written

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WebService(Namespace "Seneca.Ian.Webservices",
Description "Example web service that returns
warp server information") WebServiceBinding(Conf
ormsTo 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 pub
lic class serverInfo System.Web.Services.WebServ
ice public serverInfo ()
//Uncomment the following line if using designed
components //InitializeComponent()
WebMethod(Description"This method
returns a greeting and the time of day.")
public string whatTime()
System.Net.NetworkInformation.IPGlobalProperties
thisServer System.Net.NetworkInformation.IPGlo
balProperties.GetIPGlobalProperties()
return "Good day mate! - It is "
DateTime.Now.ToLongTimeString() "
at host " thisServer.HostName "
(domain " thisServer.DomainName ")"

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Web Service Class

• The new class created derives from the class
  System.Web.Services.WebService
• This allows you to use ASP.Net objects such as
  Application, Session, Server and User

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Documenting a Web Service

• Documentation (comments) is extremely important
  as it tells subscribers how to use your Service
• WebService declares a namespace, which you
  choose, and includes a Description for the
  Service
• The namespace should include a reference to your
  server and you, i.e. Seneca.Ian.Webservices
• WebMethod includes a Description for each method
  and must precede each method

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Testing Your Service

• Enter the URL of your service into a browser and
  it will display the Service information page, if
  your code is properly constructed

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• Select Service Description and you will see the
  XML code for the Service
• Select a Method name and you will see the XML
  code for the Method when you are working on the
  server
• If you are working on the Local Machine you will
  see a test page, click the test button and you
  will see the results of a call to the Method