9. Web Services

2 Microsoft Objectives “Web Services are poised to change the future of software development...” WebServices

3 Microsoft Web services? “Web services are web apps that return data, not presentation. Since applications are typically about accessing data, web services are poised to become the next evolutionary step in distributed software development...” Why? –cross-platform application development –legacy system integration obj Web server obj XML

4 Microsoft Overview Web services involve many technologies: –WSDL to learn about web service –to call: proxy objects, SOAP, XML, HTTP and.ASMX pages obj Web server obj client app proxy method call HTTP request SOAP msg (XML). asmx web service method call WSDL

5 Microsoft Example Google A great search engine – –but what if I want my own GUI?

6 Microsoft Google web service Google offers a web service that performs searches for you Why? –clients can build custom GUIs –google.com can make money! // ask google to search for us... google = new GoogleSearchService(); result = google.doGoogleSearch("4a8/TvZQFHID0WIWnL1CMmMx0sNqhG8H", txtSearch.Text, 0, 10, false, "", false, "", "", ""); // display resulting URLs... foreach (ResultElement re in result.resultElements) lstURLs.Items.Add(re.URL);

7 Microsoft Working with web services Two steps: 1.build a web service 2.build clients to use it

8 Microsoft (1) Building a web service Start by creating a project of type “ASP.NET Web Service”

9 Microsoft A web service is… One or more objects that respond to web-based method calls –there is no GUI design to a web service –only raw classes with methods… public class Service1 : System.Web.Services.WebService {. }

10 Microsoft Example Looks like C#, but keep in mind these are web-based methods –client could be calling from any platform –parameters passed using XML public class Service1 : System.Web.Services.WebService { [WebMethod] public int Add(int x, int y) { return x + y; } [WebMethod] public string[] Attendees() { > } attribute inherit

11 Microsoft (2) Building a client Start by creating a client… –WinForm, WebForm, console-based, anything you want! –for fun, let's use VB…

12 Microsoft Reference the component As usual, we need to reference component –this will activate IntelliSense –this will make sure we call it correctly –this will enable underlying XML + SOAP communication How? –project references, right-click, Add web reference… –type URL for web service, e.g. service name class name web server

13 Microsoft Program against component Treat web service like any other class! –use new to create instances –make method calls –pass parameters Private Sub Button1_Click(...) Handles Button1.Click Dim i, j, k As Integer i = CInt(TextBox1.Text) j = CInt(TextBox2.Text) Dim obj As localhost.Service1 obj = New localhost.Service1() k = obj.Add(i, j) MessageBox.Show("Sum = " + k.ToString()) End Sub

14 Microsoft Underlying execution… Here's what the call to Add() actually looks like: Web server obj client app proxy obj.Add(i, j); HTTP request: Service1.asmx asmx web service obj.Add(10, 20);

15 Microsoft Summary Pretty powerful stuff! Lots of technology be used underneath: –XML for parameter-passing –SOAP as protocol –HTTP –ASP.NET –IIS

16 Microsoft References Books: –Y. Shohoud, "Real World XML Web Services: for.NET and VB.NET Developers" Web sites: –

17 Microsoft Lab? Work on lab #6, "Web Services"…