Web Services

1
Web Services

• ASP.NET

2
Introduction

• Today's Web sites that just deliver user
  interface pages to browsers
• Next generation is programmable Web sites that
  link organizations, applications, services, and
  devices with one another.
• The common language runtime provides built-in
  support for creating and exposing Web Services
  (XML Web Services)
• Web Services make web a virtual library of
  ready-made code.

3
Progression

• They are a technology that make interactions of
  objects over the internet possible !
• Natural progression
• OO-languages lets objectsinteracts within the
  same application
• Protocols such as COM let objects on the same
  same computer but in different applications
  interact.
• Protocols such as DCOM let objects on different
  computers but the same network, interacts
• Web services lets objects on different computers
  interact over the internet.

4
What is a Web Service ?

• A component of programmable application that can
  be accessed using standard web protocol.
• Using XML messages transmitted over the HTTP
  protocol.
• A black box that
• accepts requests from a consumer (an application
  or a web application)
• performs a specific task
• Returns the result (self describing xml document)
• The user can use it as if it was a local
  component
• Dont need to know anything about how the
  service function
• Only the parameters and the result

5
Invoke your first web service 1

• Make a new project
• Rigth on the Reference folder in Solution
  explorer. Add Web reference.
• Type http//live.capescience.com/wsdl/AirportWeath
  er.wsdl in the Adress bar
• Click add reference
• Make a web form (see next slide)

6
Add web reference
7
Invoke your first web service 2
8
Invoke your first web service 3

• private void Button1_Click(object sender,
  System.EventArgs e)
• com.capescience.live.AirportWeather aw new
  com.capescience.live.AirportWeather()
• com.capescience.live.WeatherSummary ws
  aw.getSummary(TextBox1.Text)
• ListBox1.Items.Clear()
• ListBox1.Items.Add(ws.location)
• ListBox1.Items.Add("Wind " ws.wind)
• ListBox1.Items.Add("Sky " ws.sky)
• ListBox1.Items.Add("Temperature " ws.temp)
• ListBox1.Items.Add("Humidity " ws.humidity)
• ListBox1.Items.Add("Barometer " ws.pressure)
• ListBox1.Items.Add("Visibility "
  ws.visibility)

9
Invoke your first web service 4
10
What happens ?

• When you make a web reference Visual Studio reads
  the WSDL file
• Generate proxy class
• When you call the method from the remote server
  .NET translate your call into SOAP and transmit
  it to the remote method and receives the result
  in SOAP and convert it to .NET datatype
• By default the client uses synchronous methods to
  communicate with the Web service
• The client wait for the result

11
Greeting.asmx
using Systemusing System.Collectionsusing
System.ComponentModelusing System.Datausing
System.Diagnosticsusing System.Webusing
System.Web.Services namespace
MiFirstWebService public class Service1
System.Web.Services.WebService public
Service1() InitializeComponent() WebM
ethod public string HelloWorld() return
"Hello World"
12
Definition of a Web service

• using Systemusing System.Web.Servicesusing
  System.Xml.Serialization
• Next, it imports the namespace.
• public class Service1
• Next, the class is declared.
• WebService(Namespace"http//www.rhs.dk/webservic
  es/")
• Defines a namespace for the class
• Each XML Web service needs a unique namespace in
  order for client applications to distinguish it
  from other services on the Web.
• Allow us to organize the programming components
  into categories.
• WebMethod
• any methods that will be accessible as part of
  the service have the attribute WebMethod.
• Web service files saved under the .asmx file
  extension.
• Like .aspx files, these are automatically
  compiled by the ASP.NET runtime when a request to
  the service is made (subsequent requests are
  serviced by a cached precompiled type object

13
Greeting.asmx
14
HTTP Request-Response

• Web services rely on the mechanism of HTTP
  Request-Response system.
• All information we submit to a web service is
  sent as a HTTP Request
• Contains the data
• HTTP GET http//localhost8083/greeting.asmx/Hel
  lo?namepoulh
• HTTP POST use the body of the transmission to
  carry the name-value pairs to the web service
• All Information we get back from the Web Service
  is a HTTP Response.
• Contains the result data
• Makes it easy to acces from a browser

15
HTTP GET
16
HTTP POST
17
HTTP

• We need to be able to
• pass more than integers and strings.
• Ex. Objects, datasets .
• Web services use XML to describe data sent from
  the consumer and returned from the web service.

18
SOAP (Simple Object Acces Protocol)

• SOAP is a lightweight protocol for exchange of
  information over the internet.
• SOAP is not restricted to name/value pairs
• Defined by W3C
• Uses XML syntax to format its content.
• The SOAP request is submitted as part of an HTTP
  post request.
• Provides an effective way to call all sorts of
  methods

19
Advantages of using SOAP

• HTTP is pervasive. It can travel to any point on
  the internet regardless of hardware or firewall.
• Because is SOAP is XML based, it can be
  interpreted by a wide variety of software on many
  operating systems.

20
SOAP example
21
SOAP

• The SOAP message consist of an envelope that
  contains a body, each of them is identified with
  a specific XML tag.
• It invokes a method called Hello
• The parameter is called name of type string.
• The response is of type String wrapped as an XML
  element.

22
Datatypes

• Various data types are supported by SOAP and can
  be passed to and returned from Web Service
  methods
• Primitive
• Enum Types
• Arrays of Primitives, Enums
• Classes and Structs
• DataSet
• ..

23
SOAP

• Web Services are based on open protocols such as
  the Simple Object Access Protocol (SOAP)
• This client technology can also be used to
  consume non-ASP.NET Web Services.

24
Web Service AttendeeWebservice

• using Systemusing System.Collectionsusing
  System.ComponentModelusing System.Datausing
  System.Diagnostics
• using System.Webusing System.Web.Services using
  System.Data.OleDb
• namespace AttendeeWebservice
• public class Service1 System.Web.Services.WebSe
  rvice
• public Service1()
• InitializeComponent()
• WebMethod
• public string findAttendee(string fname, string
  lname)
• return getAttendee(fname, lname)

25
Web Service AttendeeWebservice

• private string getAttendee(string firstName,
  string lastName)
• IDbConnection dbConn String sConnection
• string result
• sConnection "ProviderMicrosoft.Jet.OLEDB.4.0"
  "Data Sourcec/Attendees.mdb"
• dbConn new OleDbConnection(sConnection)
• dbConn.Open()
• string sql "Select From Attendees "
• if (firstName ! "" lastName ! "") sql
  " where FirstName '" firstName "' and
  LastName '" lastName "'"
• IDbCommand dbCmd
• dbCmd new OleDbCommand()
• dbCmd.CommandText sql
• dbCmd.Connection dbConn
• IDataReader dbReader
• dbReader dbCmd.ExecuteReader()
• if (dbReader.Read())
• result dbReader"AID".ToString() " "
  result dbReader"FirstName".ToString() "
  "
• result dbReader"LastName".ToString() "
  " result dbReader"Email".ToString()
  " "

26
AttendeeWebservice(continued)

• WebMethod
• public DataSet getAllAttendee()
• return getAll()
• private DataSet getAll()
• IDbConnection dbConn
• String sConnection
• sConnection "ProviderMicrosoft.Jet.OLED
  B.4.0" "Data Sourcec/Attendees.mdb"
• OleDbConnection con new
  OleDbConnection(sConnection)
• string sql
• sql "Select From Attendees Order By
  LastName Asc, FirstName Asc"
• OleDbDataAdapter DataAdapter new
  OleDbDataAdapter(sql,con )
• DataSet dataSet new DataSet()
• DataAdapter.Fill(dataSet, "Attendees")
• return dataSet

27
WSDL (Web Service Description Language)

• An XML file thats define how the interaction
  between a Web Service and its consumer will
  occur.
• A cross-platform standard from W3C.
• Can define interaction independent of platform
  (Unix, Mac, Windows..) and programming language
  (ASP.NET, java).
• Finding a description (WSDL) of a web service
• http//localhost8083/findattendeeservice.asmx?wsd
  l
• Gives all the information we need to
  use/communicate with the web service.

28
WSDL files define

• The data types that it can process
• The methods that it exposes
• The URLs through which those methods can be
  accessed.

29
WSDL
30
Consuming a Web Service 1
Consumer
Application
7
1
Proxy
6
2
5
3
Web Service
4
31
Consuming a Web Service 2

• The application executes a function in the proxy
  code.
• Passing parameters
• The proxy receives the call and formulates the
  request to the webservice
• The function call is sent to the web service.
• Across LAN or Internet.
• The web service uses the parameters to executes
  its function, builds XML for the result.
• The XML result is sent to the proxy at the
  consumer.
• The proxy parses the XML result and retrieve the
  values.
• The application recieves the values from the
  proxy function.

32
Proxy

• A Proxy is a stand in for te actual code you want
  to call.
• Managing the call across the network.
• The proxy resides on the consumers machine
• React as an relay between the consumer and the
  web service. The web service is mapped in the
  proxy.
• The WSDL file is use to create the proxy
• WSDL, tells which methods can be called, the
  parameters and the result.
• The proxy handles all the network related work.
• The consumer dont know anything about sending
  data and WSDL.
• The consumer use the web service as if it was a
  part of the application itself.

33
Using findAttendeeservice.aspx
34
Add web reference http//localhost/AttendeeWebser
vice/Service1.asmx
35
consumeAttendeeWebservice.aspx

• private void Button1_Click(object sender,
  System.EventArgs e)
• localhost.Service1 wsAttendee new
  localhost.Service1()
• string firstname TextBox1.Text
• string lastname TextBox2.Text
• TextBox3.Text wsAttendee.findAttendee(firstname
  , lastname)
• private void Button2_Click(object sender,
  System.EventArgs e)
• localhost.Service1 wsAttendee new
  localhost.Service1()
• DataGrid1.DataSource wsAttendee.getAllAttendee(
  )
• DataGrid1.DataBind()

36
Web service discovery

• How to find a web service ?
• Disco
• A Microsoft standard for creating discovery
  documents. Not used outside the .NET world
• UDDI
• Universal Description, Discovery and Integration
• A method for finding services by referring to a
  central directory. Developed by several
  industrial partners IBM, Microsoft
• See www.uddi.org