Session 7 : The Web

1
Session 7 The Web

• Peter Villadsen

2
Matters arising

• Have I mentioned CodeProject?
• www.codeproject.com

3
Adding richer content to WinForms

• The .NET framework is an evolution, not a
  revolution.
• Before the advent of .NET and managed code, there
  was a concept called COM objects.
• These were higherlevel versioned objects packaged
  such that the implementation was securely hidden.
• Subsequently, a standard was defined for COM
  objects with a visual representation (ActiveX).
• There are A LOT of these out there.
• Fortunately, it is possible to use these on forms.

4
Demo Controls

• Demo
• Agent
• Spreadsheet
• MSChart

5
The Web in General

• The web has revolutionized our lives.
• It gives us possibilities to reach out into the
  world that we have never had before.
• It gives businesses a way of conducting business
  electronically.
• We're only just starting to utilize the potential.

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Web technologies

• We will concentrate on
• Web pages, using ASP.NET
• Web services.
• We will not look too much into the technology
  that transports the data from one end to the
  other.
• (Except maybe for this).

7
The Web Server

• The web server is the program that sends HTML to
  the browser.
• The browser requests a page through a URL.
• The browser uses the DNS (Domain Name Server) to
  convert the domain name of the URL into an IP
  Address.
• Demo nslookup ltsitegt using IP address in
  browser.
• The site with that IP address is then hit (on
  port 80).
• The server examines the rest of the URL
  (stripping the domain) and either just sends the
  HTML back or executes code generating HTML.
• This is a server, meaning a number of clients can
  be served at once.
• The MS Internet explorer is called IIS (Internet
  Information Server).

8
HTML. The history

• In 1989, Tim Berners-Lee worked at CERN in
  Geneva.
• Particle physics requires cooperation from teams
  all over the world. A method for cross
  referencing and accessing research papers was
  needed.
• While reading one paper, you could instantly
  examine references to others, forming a web of
  information. The hyperlink was invented.
• Tim B-Lee based the format of the text on (the
  already existing) SGML. He called it HTML,
  HyperText Markup Language. To transfer the data
  between machines, he invented HTTP, HyperText
  Transfer Protocol.

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HTML

• HTML is now a standard. There are many browsers
  available on any platform.
• HTML is raw text, with tags defining the layout.
• Demo
• This servers perfectly for static contents, where
  the information does not change much.
• Active Server Pages emerged from MS (and other
  technologies from other vendors), allowing code
  to be mixed in.
• The current incarnation is ASP.NET, allowing
  managed code to be used to provide the code.

10
Dynamic ASPX pages

• Demo. Make a simple html page and put it in a
  suitable directory.
• Demo. Take the html page from before and make it
  dynamic, such that it uses code to achieve its
  result.
• Rename to .aspx
• Insert code with lt gt metatags.
• If you wanted to, you could still write code this
  way, but now there are easier and better ways,
  using VS.
• Now, you can use the knowledge you have from
  building windows forms to build web forms.
• Works by adding Server controls that are
  interpreted at the server. The generated HTML
  code is sent back to the browser.

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Source code

• It is still perfectly possible to mix in code
  with the page itself.
• In this way, everything is collected in one
  place.
• BUT It causes a dangerous coupling between
  content and logic.
• Better to use code behind files (or partial
  classes).

lthtmlgt ltscript language"C" runatservergt
void SubmitBtn_Click(Object sender,
EventArgs e) Message.Text "Hi "
Server.HtmlEncode(Name.Text) ", you selected "
Category.SelectedItem " on "
MyCal.Date.ToShortDateString()
lt/scriptgt ltbodygt ltcentergt
ltform action"intro7.aspx" method"post"
runat"server"gt ....
ltaspbutton text"Lookup" OnClick"SubmitBtn_Click
" runat"server"/gt lt/formgt
lt/centergt lt/bodygt lt/htmlgt
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Server controls

• The use of server controls allows user interfaces
  to be written more easily.

lthtmlgt ltheadgt ltlink rel"stylesheet"href
"intro.css"gt lt/headgt ltbodygt
ltcentergt ltform action"intro5.aspx"
method"post" runat"server"gt
ltaspadrotator AdvertisementFile"ads.xml"
BorderColor"black" BorderWidth1
runat"server"/gt lth3gt Name
ltasptextbox id"Name" runat"server"/gt
Category ltaspdropdownlist id"Category"
runatservergt
ltasplistitem gtpsychologylt/asplistitemgt
ltasplistitem gtbusinesslt/asplisti
temgt ltasplistitem
gtpopular_complt/asplistitemgt
lt/aspdropdownlistgt lt/h3gt
ltaspbutton text"Lookup" runat"server"/gt
lt/formgt lt/centergt lt/bodygt lt/htmlgt
13
Demo Writing a Web page

• Create a new project of type ASP.NET Web
  Application.
• Add some controls.
• Run from the browser.
• Check the application within the IIS.

14
Web Services

• XML Web services provide a simple, flexible,
  standards-based model for binding applications
  together over the Internet. Middle-tier business
  functionality exposed by way of standard Web
  protocols is known as XML Web services.
• All implementation details are encapsulated.
• Web services accept SOAP messages and send back
  SOAP replies.
• Their interface is described in a special XML
  document with the extension WSDL.
• This information may be read by interested
  clients who then know how to interact with it.

15
Web Services

• UDDI specifies a mechanism for Web service
  providers to advertise the existence of their Web
  services, and for Web service consumers to locate
  Web services of interest.
• It is extremely easy to create web services and
  web services consumers using VS.NET.

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SOAP

• Simple Object Access Protocol is the format of
  the messages that go over the wire to invoke web
  services.
• This is an XML schema.
• SOAP messages carry both an envelope and a
  payload.
• ltenvEnvelope xmlnsenv"http//www.w3.org/2003/05
  /soap-envelope"gt
• ltenvHeadergt
• lt/envHeadergt
• ltenvBodygt
• ltmalert xmlnsm"http//example.org/alert
  "gt
• ltmmsggtPick up Mary at school at
  2pmlt/mmsggt
• lt/malertgt
• lt/envBodygt
• lt/envEnvelopegt

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WSDL

• Web Service Description Language
• This is the document that describes the web
  service. It contains the following sections
• Types
• Messages
• Operations
• Port types
• Bindings
• Ports
• Services

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WSDL

• Types describe the types of the data contained in
  the messages.
• This is usually described in the XSD (schema
  definition language).
• Messages are composed of parts.
• Each part refers to a type in the Types section.
• A Port Type is a set of messages grouped into
  operations.
• Operations represent a single unit of work
  performed by the service. Think of an operations
  as a method with in, out parameters and exception
  cases.
• Bindings define how a given operation maps to a
  specific protocol.
• A Port associates a bindig with a protocol
  specific address

19
Demo

• Create a simple class and put it in a suitable
  web server directory.
• Add the stuff that is needed to make this a web
  service.
• Demonstrate that it works.
• Use the VS IDE to do the same
• Create a simple web service (call it
  SimpleValidator) to validate a credit card
  number.
• View the .asmx file in the browser.
• Show the WSDL in the browser
• http//localhost/SimpleValidator/Service1.asmx?
  WSDL.

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Web Services Clients

• Clients (consumers of web services) certainly do
  not want to deal with the low-level plumbing
  involved in constructing SOAP messages,
  marshalling parameters etc.
• An clean object model is presented instead.
• The bridge between the two worlds is the Proxy.
• The proxy is generated by the wsdl tool.
• (This is done by the VS environment for you).

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Demo

• Create the proxy file for the web service written
  before.
• Wsdl http//.../MyService.asmx?wsdl

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Proxy

• The generated proxy is what supplies the clean OO
  abstraction of the web service.

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Client

• The Mappoint web service