9. Web Services

Report
9. Web Services
Objectives
“Web Services are poised to change the future of software
development...”
• WebServices
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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
XML
obj
Web server
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obj
obj
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Overview
• Web services involve many technologies:
– WSDL to learn about web service
– to call: proxy objects, SOAP, XML, HTTP and .ASMX pages
web service
WSDL
client app
obj
obj
method call
method call
obj
.asmx
proxy
Web server
SOAP msg (XML)
HTTP request
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Example
• Google
• A great search engine
– www.google.com
– but what if I want my own GUI?
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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);
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Working with web services
• Two steps:
1. build a web service
2. build clients to use it
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(1) Building a web service
• Start by creating a project of type “ASP.NET Web Service”
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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
{
.
.
.
}
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Example
• Looks like C#, but keep in mind these are web-based methods
– client could be calling from any platform
inherit
– parameters passed using XML
attribute
public class Service1 : System.Web.Services.WebService
{
[WebMethod]
public int Add(int x, int y)
{
return x + y;
}
[WebMethod]
public string[] Attendees()
{
<<open DB, read attendees into array, return it>>
}
}
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(2) Building a client
• Start by creating a client…
– WinForm, WebForm, console-based, anything you want!
– for fun, let's use VB…
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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.
• http://localhost/WebService/Service1.asmx
web
server
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service
name
class
name
12
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
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Underlying execution…
• Here's what the call to Add() actually looks like:
web service
client app
obj.Add(i, j);
proxy
<Add>
<n1>10</n1>
<n2>20</n2>
</Add>
obj
obj.Add(10, 20);
.asmx
Web server
HTTP request: Service1.asmx
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Summary
• Pretty powerful stuff!
• Lots of technology be used underneath:
– XML for parameter-passing
– SOAP as protocol
– HTTP
– ASP.NET
– IIS
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References
• Books:
– Y. Shohoud, "Real World XML Web Services: for .NET and VB
.NET Developers"
• Web sites:
– http://msdn.microsoft.com/webservices
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Lab?
• Work on lab #6, "Web Services"…
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