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Web Services in .NET (1)

These slides are meant to be for teaching purposes only and only for the students that are registered in CSE4413 and should not be published as a

book or in any form of commercial product, unless written permission is obtained.

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What is a Web Service?• A Web Service (WS) is a class (or many

classes) that resides in a computer and it is accessible from another computer, in the sense that clients can call methods of this class remotely.

• In .NET, any method of a class can be equipped to be accessed remotely. All it needs is to associate the attribute [WebMethod] with that method.

[ WebMethod ]

public void MyMethod( …) { …}

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Web Services vs “Local” Services …

System calls are written in some language (part of the OS).

SOAP is written in XML.

Access is done via local system calls (managed by the local operating system).

Access is done via “remote system calls” managed by HTTP and SOAP (Simple Object Access Protocol) a protocol that allows calling remote methods).

Class produces DLL file which is stored in local computer, and it is accessed from classes residing in same computer.

Class produces DLL file which is stored in local computer, and it is accessed from classes residing in some other computer

Local serviceWeb service

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Web Services vs “Local” Services …/

We learn about local methods via the API.

We learn about Web Services via UDDI (Universal Description Discovery and Integration) and DISCO. [ in practice, however, so far, we learn mostly through word-of-mouth ]

API may be written in XML.WSDL is written in XML.

Documentation for a local method is provided via a local API(Application Programming Interface).

Documentation for a web method is provided via WSDL(Web Service Description Language).

Local serviceWeb service

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Evolution of the internet and the WWW (0)

Generation 0FTP, e-mail

HTML

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Evolution of the web (1)

Generation 1Static HTML

HTML

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Evolution of the web (2)

Generation 2Web Applications

HTML

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Evolution of the web (3)HTML, XML

HTML, XML

Generation 3 (under construction)Web Services

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Evolution of the web (4)

empIDHTML, XML

HTML, XML, RDF

Generation 4 (under contemplation)Semantic Web

Emp-idCheck and be able to realize that empID

and Emp-id mean the same thing.

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Benefits of Web Services …• May facilitate significant boost for developing

distributed applications.• Use standard (SOAP) for message exchange.• Use standard for interface description (WSDL),

in XML.• Independent of programming languages and

operating systems.• Utilize existing Internet protocols (HTTP usually,

but also SMTP and FTP).

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Benefits of Web Services …/• Web Services allow you to interconnect:

– Different companies– Many/any devices– Applications– Different clients

• Not just browsers

• Distribution and integration of application logic• Enable the programmable Web

– Not just the purely interactive Web• Loosely coupled (scale well)

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Comparison of various distributed (Web Services and ancestors) technologies

SOAPORB/CDR.NET object serialization

Java object serialization

Message exchange format

HTTP, HTTPS, SMTP, FTP

GIOP/IIOPbinary or OAPRMI-IIOPTransport protocol

XML data IDL-specified objects

.NET objects Java objects (binary)

Data exchange format

WSDL (XML-based)

CORBA IDL.NET Interfaces Java Interfaces Interface definition

independentindependent.NET languages (C#, VB.NET, ..)

Java Programming language

Web services

CORBA.NET Remoting

Java RMI

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Web services related .NET namespaces

• System.Web.Services– for developing Web services (e.g.: WebService, WebMethod)

• System.Web.Services.Configuration– for extending SOAP

• System.Web.Services.Description– for creating and manipulating WSDL descriptions

• System.Web.Services.Discovery– for using DISCO

• System.Web.Services.Protocols– for implementation of communication protocols (e.g. SOAP-

HTTP)• System.Xml.Serialization

– for XML serialization

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Example

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A .NET web service has a .asmx file associated with it. This is the equivalent of the .aspx file of ASP.net

applications.

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Running …

The operation (method) exposed by this web service

The URL of the web service

The WSDL (web service description

language)

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The result of invoking method

“Hello World”

The name of the Web Service.

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The code: Service1.asmx.csusing System;using System.Collections;using System.ComponentModel;using System.Data;using System.Diagnostics;using System.Web;using System.Web.Services;

namespace WebService1{

/// <summary>/// Summary description for Service1./// </summary>public class Service1 : System.Web.Services.WebService{

public Service1(){

//CODEGEN: This call is required by the ASP.NET Web Services Designer

InitializeComponent();}

#region Component Designer generated code

//Required by the Web Services Designer private IContainer components = null;

Class Service1 is our Web Service. (Subclass of

class WebService)

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…//// <summary>/// Required method for Designer support - do not modify/// the contents of this method with the code editor./// </summary>private void InitializeComponent(){}

/// <summary>/// Clean up any resources being used./// </summary>protected override void Dispose( bool disposing ){

if(disposing && components != null){

components.Dispose();}base.Dispose(disposing);

}

#endregion

// WEB SERVICE EXAMPLE// The HelloWorld() example service returns the string Hello World

[WebMethod]

public string HelloWorld(){

return "Hello World";}

}}

The web service method HelloWord()

C# attribute, that makes this method exposed as part of a web service.

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How to use the HelloWorld web service

• Any .NET application

– Console application– Windows application– Web Application

can use a Web Service.

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A console application that uses the HelloWorld Web Service

Output string “Hello World” comes from the returned value of method HelloWorld() that

had been invoked.

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The code

1. Create a console application, and 2. add access to the existing web service

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3. Find the Web Service to use. In this case, select from the local machine.

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4. Once the service is found, type the name you like to use to reference it (HelloWorldWebService, in this example).

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5. The web service is made available for use in ConsoleApplication1.

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The constructor of the web service points to the location of the .asmx file, so that the web service

is found when needs to be used.

The method HelloWorld() of this web service.

Class1 is the console application that uses (consumes) the web service.

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The consumer class: Class1

Instance variable of type HelloWorldWebService.Service1

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Class1 is the consumer, i.e., contains the code that uses the web service.

using System;

namespace ConsoleApplication1{

class Class1{

private HelloWorldWebService.Service1 myWS;

[STAThread]static void Main(string[] args){

new Class1().go();}

public void go() {

myWS = new HelloWorldWebService.Service1();Console.WriteLine( myWS.HelloWorld() );

}}

}

Declare a WebService

Create web service object.

Call web service’s method HelloWorld()