INT422 Internet III Web Programming on Windows

1
INT422 Internet III Web Programming on
Windows

• Web Services Introduction

2
Agenda

• Analyzing the Changing Needs of the Internet
• Introduction to XML Web Services
• Building XML Web Services in .NET
• Consuming XML Web Services in .NET

3
The Need for Web Services

• Growth of the B2B Internet

4
Real-World Programming Problem

• You are asked to build a system that connects a
  Car Parts Retailer to all the major car dealers
  in Ontario via their corporate networks. The
  system should allow local dealers to find parts,
  place orders, and track those orders via Canada
  Post.

Dealer Systems
Dealer Systems
Dealer Systems
Canada Post
Daimler Central System
GM Central System
Ford Central System
Car Parts Retailer
5
Obstacles to Overcome

• First, you dont own the Canada Post or Central
  Dealer systems. You MUST follow each of their
  specifications for formatting and transporting
  data
• Second you will have to constantly allow for
  changes to these specifications. In three months
  one or all of the systems could change
• Third, you have to communicate securely between
  systems, and not disclose or expose company
  secrets between any of the participants

6
The Ever Changing WWW

• When it began in the mid-Nineties, the goal of
  the Web was to get static information published
  globally
• As it matured, this goal evolved into a desire to
  link organizational data with web sites
• Next came the E-Commerce phenomenon, and
  companies opened their virtual doors to
  customers around the world.

7
Changing WWWmore

• So where is the web today? Consider some
  statistics from the 2000 US Census
• 94 of all E-Commerce transactions were
  Business-to-Business (B2B), or about 777 Billion
• Only 0.9 of total Retail sales were done on-line
  (29 Billion). In 2003 (most recent data) this
  went up, but it is still less than 2
• Source
• http//www.census.gov/eos/www/papers/estatstext.pd
  f
• Question what does this mean?

8
One Possible Answer

• Companies dont sell to customers on-line, they
  connect and sell to one another on-line (B2B)
• Therefore, what is needed are not better,
  flashier, more commercially seductive web sites,
  but rather, better mechanisms for connecting
  businesses and organizations
• The next great challenge for the web is to allow
  systems and organizations to connect to one
  another regardless of the type technology

9
Doesnt this Already Exist?

• There have been attempts made in the past to
  solve the any-to-any problem just described
• COM and DCOM in Windows
• CORBA and RMI in Java
• None has ever solved the problem totally, because
  they are all, to one degree or another, linked to
  proprietary technologies or standards
• What made the web work was its reliance on open
  standards HTML, HTTP, TCP/IP...

10
Using what works

• Proprietary solutions will never solve the
  problems of connecting proprietary systems
• Companies like Microsoft, IBM, Sun, etc. along
  with the W3C recognized this
• Together they agreed to build a solution using
  standards like XML, HTTP, and TCP/IP
• And to do it they created some new standards
  SOAP, WSDL, and UDDI

11
What are XML Web Services?
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A Few Definitions

• A class stored on one machine that can be
  accessed on another machine over a network
  (Deitel)
• An application that listens to requests coming
  to a TCP socket and reacts to the commands each
  request contains (Balena)
• A platform for building distributed applications
  using software running on different operating
  systems and devices, written using different
  programming languages. (Microsoft)
• An application that exists in a distributed
  environment, such as the Internet. A Web Service
  accepts a request, performs its function based on
  the request, and returns a response. (Sun)

13
Web Services Important Ideas

• Remote Objects
• Web Services are classes that run on a server and
  can be consumed (i.e., used) by a client over a
  network.
• Internet Based
• Web Services use standard Internet protocols to
  pass XML messages between the client and server
• Loosely Coupled
• Messages are Sent and Received, but no permanent
  connection exists between Web Services and
  Clients
• No GUI
• Web Services provide data-only. Programmers
  build GUIs that use the functionality they
  provide.

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Programmers Perspective

• Web Services are classes you use in your code.
• The Web Service class runs on a server, and you
  create a Proxy Class to stand-in for the remote
  class.
• You use the Proxy Class as if it were the remote
  object. Therefore, your code is no different
  than if the object was actually running on your
  machine.

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Understanding Web Services
Web Server
Client
Internet HTTP, TCP/IP
SOAP Message
SOAP Message
Web Service Class
Web Service Proxy Class
App Code
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A Real-World Web Service Example
Java GUI Client running on Linux
.NET Console Application
Internet HTTP, TCP/IP
Car Quotes Web Service
Web Browser Clients
Web Server running ASP.NET Client App
Web Service - http//wavendon.dsdata.co.uk/axis/se
rvices/CarRentalQuotes
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Web-based and Console Clients
18
ASP.NET XML Web Services
19
Web Programming using .NET

• ASP.NET is really two technologies in one
• Web Forms
• XML Web Services
• We now know something about Web Forms
• a way to build graphical Internet applications
  that can be run using a client browser
• But what about XML Web Services? How do they
  differ? Why have we spent so little time on them?

20
Class Re-use DLLs vs. Web Services

• When we want to write re-usable classes in .NET
  we compile them into DLLs
• DLLs must be copied to the machine that will use
  them. We then add a Reference to the DLL, and
  can then access its classes
• Web Services also contain re-usable classes. But
  they dont get compiled to DLLs that have to be
  copied to the client. Instead we add Web
  References, which link applications across the web

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What are XML Web Services?

• First, they are implemented using XML
• XML is the eXtensible Markup Language
• an unambiguous hierarchical way to represent data
  using Tags and Attributes (cf. web.config)
• XML can be parsed exactly by any system that can
  process strings
• created and maintained by the World Wide Web
  Consortium (W3C)
• XML is the standard way to represent data today

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Web Services use SOAP

• SOAP is the Simple Object Access Protocol, and is
  a standardized platform independent way to make
  remote procedure calls using XML
• Web Services receive and send SOAP Messages.
  These are XML formatted strings that contain data
  and information about that data (i.e., metadata
  like type information)
• Most programmers wont work with SOAP directly.
  You can learn SOAP later if you want to use Web
  Services in advanced ways

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Web Service Clients use WSDL

• In order for a client to use a Web Service, the
  client must know how the Web Service works
• What methods are available?
• Which types does it return?
• All this information is contained in another XML
  file called a WSDL file, short for Web Services
  Description Language
• Again, .NET will automatically generate this for
  us, so we wont dig too deeply into WSDL now

24
Building Your FirstASP.NET Web Service
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Creating the Web Service

• Web Services are hosted on a web server
• Instead of a ASP.NET Web Application, choose
  ASP.NET Web Service

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The WebService class

• Rather than having an ASPX file, Web Services use
  a GUI-less class (cs) file and a service base
  (.asmx)

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Web Services are Classes

• You create your Web Service Class in code.
• You build a class that Inherits from System.
  Web.Services.WebService
• Compare to a web form class, which Inherits from
  System.Web.UI.Page
• Any of the class methods you want remote users
  to be able to call, you mark using the WebMethod
  attribute

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A Simple Example Adding Machine

• WebService(Description "Adds two number",
• Namespace "http//tempuri.org/")
• WebServiceBinding(ConformsTo
  WsiProfiles.BasicProfile1_1)
• public class AddMachSvc System.Web.Services.WebS
  ervice
• public AddMachSvc ()
• WebMethod(Description "Returns sum of two
  inputs")
• public int AddTwoNumbers(int one, int two)
• return one two

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Adding Machine - Explained

• Your class begins with a .NET Attribute,
  contained within the characters
• System.Web.Services.WebService says this is a Web
  Service
• Description tells remote users what our Web
  Service does
• Namespace identifies Web Service uniquely using a
  URL (does NOT have to be a real URL-- cf.
  http//tempuri.org)
• using System.Web.Services
• using System.Web.Services.Protocols
• WebService(Description "Adds two number",
• Namespace "http//tempuri.org/")
• WebServiceBinding(ConformsTo
  WsiProfiles.BasicProfile1_1)
• public class AddMachSvc System.Web.Services.WebS
  ervice

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Adding Machinemore

• Now you create your class as you normally would
• Add the WebMethod() attribute to any methods
  you want to be accessible to the outside world
  remotely
• NOTE you can write non-WebMethod methods too,
  which remote users wont see or be able to use
• WebMethod(Description "Returns sum of two
  inputs")
• public int AddTwoNumbers(int one, int two)
• return one two

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Testing your Web Service

• Test your Web Service base (File gt View in
  Browser) and you will see a test web client for
  you automatically. Click the Web Method to test

32
Testing a WebMethod

• Enter values for the Web Methods arguments and
  click Invoke
• Notice the SOAP that will be generated is also
  displayed

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The SOAP Result

• When you click Invoke, the WebMethod is called
  using the arguments you entered (i.e., 5 and 6).
  The Result is sent back as a SOAP Message
• This is XML, but you can easily see the answer is
  11, and that it is an Integer

34
Wait a Minute!I thought you said Web
Services had NO GUI?That looks a lot like a GUI!
35
Web Services No GUI?

• What you saw a was a GUI, yes. But this was a
  Test Client automatically built by Visual
  Studio.NET
• Web Services require Client Applications to
  consume them
• You can use .NET, Java, Perl, or any other
  language or development tool that supports Web
  Services running on any operating system

36
Web Service Clients

• Question Does your Web Service Client have to be
  web-based?
• Answer NO! You can use ANY client you like, web
  applications being only one of many solutions
• In .NET you can use any of the different
  application types available to consume web
  services
• ASP.NET Web Apps .NET Windows Apps
• Console Apps .NET Win32 Services
• DLL Libraries Other .NET Web Services

37
Creating a Web Service Client

• Any .NET application that you want to consume a
  web service needs a Web Reference to the
  appropriate Web Service
• A Web Reference is similar
• to a regular Reference,
• except that it links to a
• remote class rather than
• a local DLL

38
Adding a Web Reference

• Now you must locate or enter the URL to the Web
  Service you wish to consume

39
Web Referencemore

• A Web Reference is created for you, and with it a
  number of files are added, the most important of
  which is Reference.vb
• This is the Proxy class that will stand-in for
  the remote object. You instantiate and use this
  class as though it were a normal class. It will
  call the WebMethods of the Web Service for you in
  the background.

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How about a Web Client?

• Build a simple ASP.NET GUI to use the
  AddingMachine Web Service, and add a Web
  Reference just as before

btnEquals
txtSecond
txtFirst
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Web Client Code

• protected void btnEquals_Click(object sender,
  EventArgs e)
• // Create an instance of an AddMachSvc
• AddMachSvc addMachine new AddMachSvc()
• // Perform service method
• lblResult.Text addMachine.AddTwoNumbers(
  int.Parse(txtFirst.Text),
• 
  int.Parse(txtSecond.Text)).ToString()

42
The Running Web Client
43
Just for fun AddingMachine on Java

• Building a client for Java is also possible, and
  the result of adding 10 and 50 is displayed below
  in the returned SOAP Message

44
Rethinking B2B CommunicationsUsing Web
Services
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Solution to our Earlier Problem

• Build a Web Service to connect the Car Parts
  Retailer to the Dealers, and use Canada Posts
  Web Services to track orders

Dealer Systems
Dealer Systems
Dealer Systems
Tracking Web Service
Canada Post Main System
Daimler Central System
GM Central System
Ford Central System
Car Parts Web Service
Car Parts Back-end System
46
Web Services Solution

• Now you dont have to worry about proprietary
  data formats--everyone will use XML and SOAP
• The individual Car Companies can build code to
  consume your Web Service and integrate it with
  their dealers systems, even if they dont have
  web-based systems
• You can access real-time parcel tracking
  information via Canada Posts own Web Services.

47
Question How could you redesignyour
assignment to useWeb Services?What advantages
would there beto doing this, if any?