MELJUN CORTES Vb.net handout understanding web service

Visual Basic .NET Programming

Understanding Web Service * Property of STI Page 1 of 8

TOPIC TITLE: Understanding Web Service Specific Objectives: At the end of the topic session, the students are expected to: Cognitive:

1. Explain what web services are. 2. Explain the Web service module. 3. Define Dynamic Discovery Document, HTML Description Page

and WSDL. 4. Explain how to create a Web service.

Affective:

1. Listen to others with respect. 2. Participate in class discussions actively.

MATERIALS/EQUIPMENT:

o topic slides o OHP

TOPIC PREPARATION:

o Have the students research about Web Service. o It is imperative for the instructor to incorporate various kinds of

teaching strategies while discussing the suggested topics. The instructor may use the suggested learning activities below to facilitate a thorough and creative discussion of the topic.

o Prepare the slides to be presented in the class.

TOPIC PRESENTATION: The topic will revolve around Web Services. This will be the suggested flow of discussion for the course topic:

1. Ask the students to tell something about web services. 2. Explain what web services are. 3. Explain the Web service module. 4. Discuss how to create a function that can be accessed through

a Web Service by providing sample codes. 5. Explain the Dynamic Discovery Document, HTML Description

Page and WSDL document. 6. Discuss how to invoke a Web Service from a browser and a

client. Give examples. 7. Explain how to create a Web service through a demonstration. 8. Conduct Quiz #7



What is Web Service Page 1 of 14

Understanding Web Service


* Property of STIPage 1 of 14

What is a What is a What is a What is a Web Service?Web Service?Web Service?Web Service?

� allows access to components by means of Internet and HTTP

� a class that is stored on one computer

that can be accessed on another computer

over the network

� supporting frameworks for the Web services:

� Open Internet Protocols

� XML Messages and SOAP

� Messages defined by Web Services

Description Language (WSDL)

What is a Web Service? A Web service is a program that allows access to components by means of Internet and HTTP. It is a class that is stored on one computer that can be accessed on another computer over the network. Prior to Web services, internal applications can only communicate internally through local are networks. Listed below are the supporting frameworks for the Web services.

• Open Internet Protocols

• XML Messages and SOAP

• Messages defined by Web Services Description Language (WSDL)

Open Internet protocols such as XML, XML Schema Definition (XSD), HTTP and Simple Mail Transfer Protocol (SMTP) are used to transmit messages over the network. SOAP stands for Simple Object Access Protocol and is the industry standard for using XML to represent data and commands in an extensible way. To accurately describe the Web service’s methods and their arguments, it must provide a contract that client applications can rely upon. Web service contract defines the purpose of the service and its operation. The contract also describes how the service can be accessed and located. WSDL is an XML-based way of providing such contract. It describes the contract information that can be read by all client applications that can work with XML. [What is a Web Service?, Page 1 of 14]

Web Service Module Page 2 of 14




Web Service Web Service Web Service Web Service ModuleModuleModuleModule

� used to group the files needed to create a Web service

� contains two files:

� .asmx

• includes the WebService directive

� .asmx.vb file

• contains the code that executes when a

Web Service method is invoked

<%@ WebService Language=”vb”

CodeBehind=”AdminUsr.asmx.vb”

Class=”WebApp.AdminUsr” %>

Web Service Module In Visual Studio 2005, Web Service module is used to group the files needed to create a Web service. It contains two files namely the .asmx

and the .asmx.vb file. The .asmx file includes the WebService

directive that specifies the language used, the name of the code file and the name of the class used in referencing the service. The following example declares a service named AdminUsr written in

VB.Net, using the Admin.asmx.vb module for the code and in the

WebApp namespace.

<%@ WebService Language=”vb”

CodeBehind=”AdminUsr.asmx.vb”

Class=”WebApp.AdminUsr” %>

On the other hand, the .asmx.vb file contains the code that executes

when a Web Service method is invoked. The code inherits from the System.Web.Services.WebServices class and provides direct

access to common ASP.Net objects such as Session, Server,

Application and User.

[Web Service Module, Page 2 of 14]



Adding Public Subroutines or Functions Page 3 of 14




Adding Public Adding Public Adding Public Adding Public Subroutines or FunctionsSubroutines or FunctionsSubroutines or FunctionsSubroutines or Functions

� Example:

<WebMethod()> Public Function

AddAdminUsr(ByVal strName As

String) As String

‘ Functionality to add a user and

return new ID

…

Return strNewId

End Function

<WebMethod()> Public Sub

DeleteAdminUsr(ByVal strId As

String)

‘ Functionality to delete a user based

on ID

…

End Sub

Adding Public Subroutines or Functions Web Service methods can be created by using standard method syntax for subroutines or functions. Then, the Web Service method must be

marked as public and use the WebMethod class attribute.

The following example shows how to create a function that can be accessed through a Web Service. <WebMethod()> Public Function AddAdminUsr(ByVal

strName As String) As String

‘ Functionality to add a user and return new ID

…

Return strNewId

End Function

<WebMethod()> Public Sub DeleteAdminUsr(ByVal strId

As String)

‘ Functionality to delete a user based on ID

…

End Sub

In addition, a description can be added to the method by specifying the Description argument of the WebMethod attribute. Example is

shown below. <WebMethod(Description:=”This method performs an

action”)> Public Sub PerformsAction()

…

End Function

[Adding Public Subroutines or Functions, Page 3 of 14]

Dynamic Discovery Document Page 4 of 14




Dynamic Dynamic Dynamic Dynamic Discovery DocumentDiscovery DocumentDiscovery DocumentDiscovery Document

� contains information about the Web service

� used to locate and discover Web services

� automatically created by ASP.NET

� return the details of all Web Services

� uses the .vsdisco file extension

� used to exclude particular folders from the dynamic discovery process

Dynamic Discovery Document Dynamic discovery document is a document that contains information about the Web service. It is used to locate and discover Web services. The dynamic discovery document is automatically created by ASP.NET and will return the details of all Web Services contained in the root directory and any sub-directories. It uses the .vsdisco file extension. It is also used to exclude particular folders from the dynamic discovery process. [Discovery Document, Page 4 of 14]



HTML Description Page and WSDL Document Page 5 of 14




HTML Description Page HTML Description Page HTML Description Page HTML Description Page and WSDL Documentand WSDL Documentand WSDL Documentand WSDL Document

� The HTML description page

� describes Web services methods and

arguments

� displayed when Web service URL is entered

without specifying a particular method

name

� contains simple test utility methods

� provides test facilities for each methods of

the Web service

� allows you to provide parameter through

an input field

� follows the format:

http://webservername:port/webservi

ce.asmx.

� Example:

http://localhost:3163/MyService.as

mx

HTML Description Page and WSDL Document Page 6 of 14




HTML Description Page HTML Description Page HTML Description Page HTML Description Page and WSDL Documentand WSDL Documentand WSDL Documentand WSDL Document

� Web Services Description Language (WSDL)

� describes methods, arguments and

responses of a Web service

� created automatically by adding the ?WSDL

switch to the Web service URL

� Example:

http://localhost:3163/MyService.as

mx?WSDL

HTML Description Page and WSDL Document The HTML description page describes Web services methods and arguments. It is displayed when Web service URL is entered without specifying a particular method name. The URL follows the format http://webservername:port/webservice.asmx. For example,

to display the HTML description page of a Web service named MyService, the URL is

http://localhost:3163/MyService.asmx

The HTML description page contains simple test utility methods. It provides test facilities for each methods of the Web service. It allows you to provide parameter through an input field. Upon entering the values and clicking the Invoke button, the Web service executes and displays the result in XML format. It also displays additional descriptions about each method if the Description parameter for the WebMethod

attribute is specified. In Visual Studio 2005, another way to display the HTML description page is by right-clicking the .asmx file in Solution

Explorer and then clicking View in Browser. The Web Services Description Language (WSDL) document describes methods, arguments and responses of a Web service. It is created automatically by adding the ?WSDL switch to the Web service URL. For

example, to display the WSDL of the Web service named MyService,

the URL will be:

http://localhost:3163/MyService.asmx?WSDL

[HTML Description Page and WSDL Document, Pages 5-6 of 14]

Invoking a Web Service from a Browser and a Client Page 7 of 14




Invoking a Web Service Invoking a Web Service Invoking a Web Service Invoking a Web Service from a Browser from a Browser from a Browser from a Browser

and a Clientand a Clientand a Clientand a Client

� To invoke a Web Service from a browser:

� enter the URL of the service, specify the method name to run as well as parameter

values

� Syntax:

http://webservername/vdir/webservi

cename.asmx/MethodName?parameter

=value

� Examples:

http://www.myserver.com/User/Admin

Usr.asmx/AddAdminUsr?strName=Man

ny

<?xml version=”1.0” ?>

<string

xmlns=http://tempuri.org/>43-

124-21</string>

Invoking a Web Service from a Browser and a Client To invoke a Web Service from a browser, enter the URL of the service, specify the method name to run as well as parameter values. The following syntax is used to invoke a Web Service: http://webservername/vdir/webservicename.asmx/MethodN

ame?parameter=value

The following example shows how to invoke a Web Service. This code

calls the AddAdminUsr method of the AdminUsr.asmx Web Service in

the Users virtual directory on the myserver.com Web server. It also

passes in a parameter value of the admin user name Manny.

http://www.myserver.com/User/AdminUsr.asmx/AddAdminUs

r?strName=Manny

The Web Service will return XML output containing the results of the






* Property of STI

Page 8 of 14



� HTTP GET method

� used to send the form data to the Web

server

� most commonly used for testing purposes

� SOAP protocol

� used for real application-to-application

communication

� difference between the HTTP-GET and

SOAP

� the way of sending data to the Web server




* Property of STI

Page 9 of 14



� To invoke a Web service from a client:

� add a Web reference to the Web Service

� enter the URL for the .asmx file

� select the required references

� create the client code for accessing a

component

� Example:

Private Sub btnSubmit_Click(ByVal

sender As System.Object, _

ByVal e As System.EventArgs)

Handles btnSubmit.Click

’Services is the given namespace

Dim usr As New Services.user( )

MessageBox.Show(usr.AddUser(txtNam

e.Text))

End Sub

execution as shown in the following example. The results show a String value of 43-124-21 being returned as a new identity of the added user.

<?xml version=”1.0” ?>

<string xmlns=http://tempuri.org/>43-124-21</string>

This approach uses the HTTP-GET protocol. The HTTP GET method is used to send the form data to the Web server. The form data is appended onto the URL in the Address field. This is most commonly used for testing purposes. For real application-to-application communication, SOAP protocol is used instead. SOAP is a specification for exchanging structured information across networks and computer platforms using XML and HTTP. The main obvious difference between the HTTP-GET and SOAP protocols is the way data is sent to the Web server. In HTTP-GET, data is part of the URL while in SOAP, it uses XML. For this reason, SOAP is better in terms of performance, security and scalability than HTTP-GET. Depending on the client, Web Service can be invoked from a client application either thru a Windows Form or a Web Forms application. If the client is written in Visual Basic .NET, you can use the following process:

1. Add a Web reference to the Web Service. 2. Enter the URL for the .asmx file. 3. Select the required references. 4. Create the client code for accessing a component. Use the

appropriate namespaces. When Web reference is added to the client project, Visual Basic .NET creates a proxy class that hides the complexity of calling a Web Service. This proxy allows the use of early binding when connecting to the service, as if the components were accessible within a local assembly. In the following example, the required Web Service has taken a web reference, and the Web reference has been renamed as the Services

namespace. A command button named btnSubmit and a text box

named txtName have been placed on a Windows Forms form with the

following code for the btnSubmit_Click event handler:

Private Sub btnSubmit_Click(ByVal sender As

System.Object, _

ByVal e As System.EventArgs) Handles btnSubmit.Click

’Services is the given namespace

Dim usr As New Services.user( )

MessageBox.Show(usr.AddUser(txtName.Text))

End Sub

When the preceding code is executed, a new user is created. The txtName text box specifies the name of the new user, and the

AddAdminUsr method creates a message box that displays the new

identity. [Invoking a Web Service from a Browser and a Client, Pages 7-9 of 14]



Demo: Creating a Web Service Page 10 of 14



* Property of STI

Page 10 of 14

Demo: Creating a Demo: Creating a Demo: Creating a Demo: Creating a Web ServiceWeb ServiceWeb ServiceWeb Service

� Open Visual Studio 2005.

� File > New Web Site

� select ASP.NET Web Service

� set Location to File System

� set Language to Visual Basic then click OK

� delete the asmx file

� delete the vb file

� right-click on the project name and click

Add New Item

� select Web Service in the Templates list then set the Web service and click Add

� right-click on the App_Code and click Add New Item

� select Class from the Installed Templateslist

� set the class name then click Add




* Property of STI

Page 11 of 14


� open the Code Editor for the .asmx file,

locate the Public Class definition then modify the WebService attribute

<WebService(Namespace:=”http://tem

puri.org/”, _

Description:=” Web service demo

information.”

)> Public Class WebServiceDemo

� delete the code:

<WebMethod()> _

Public Function HelloWorld()

As String

Return "Hello World"

End Function




* Property of STI

Page 12 of 14


� To define the Web Service methods:

� Add WebMethod attribute and Web service

method

<WebMethod(Description:="Retrieves

welcome message.")> _

Public Function GetMessage()

As String

GetMessage = "Learning Web

services is fun!"

End Function

� To test the Web Service:

� right-click on the project name and select

Build Web Site

� right-click the .asmx file, and then click View in Browser

Demo: Creating a Web Service

1. Open Visual Studio 2005. 2. In the menu bar, click File and then click New Web Site. 3. In the New Web Site window, select ASP.NET Web Service. In

the Location information, make sure that the drop-down list is set to File System. Then, set the location of your Web application.

4. For the Language information, select Visual Basic. Click OK. 5. In the Solutions Explorer, delete the asmx file named

Service.asmx. 6. Delete the vb file named Service.vb. 7. Right-click on the project name and click Add New Item. The

Add New Item window is displayed. 8. In the Templates list, select Web Service. In the Name field,

set the Web service name to WebServiceDemo.asmx. Click Add.

9. In the Solutions Explorer, right-click on the App_Code and click Add New Item. The Add New Item window is displayed.

10. In the Installed Templates list, select Class. In the Name field, set the class name to WebServiceDemo.vb. Click Add.

11. Open the Code Editor for WebServiceDemo.asmx, locate the Public Class WebServiceDemo definition, and then modify the WebService attribute to include the following Description parameter value:

Web service demo information.

12. Verify that the WebService attribute now looks as follows: <WebService(Namespace:=”http://tempuri.org/”, _

Description:=” Web service demo information.”

)> Public Class WebServiceDemo

13. Locate and delete the following code. This code is a sample

Web service method that is created automatically.

<WebMethod()> _

Public Function HelloWorld() As String

Return "Hello World"

End Function

To define the Web Service methods:

14. Add the following WebMethod attribute and Web service

method. This method returns a message.

<WebMethod(Description:="Retrieves welcome

message.")> _

Public Function GetMessage() As String

GetMessage = "Learning Web services is fun!"

End Function

To test the Web Service:

15. Build the project. In Solution Explorer, right-click on the project

name and select Build Web Site. 16. In Solution Explorer, right-click WebServiceDemo.asmx, and

then click View in Browser to display the HTML description page. The page should look similar to the one on the next page.






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Page 13 of 14


� click the Service Description hyperlink




* Property of STI

Page 14 of 14


� click the Back button

� click the hyperlink of the method of the Web Service

� click the Invoke button

17. Click the Service Description hyperlink and examine the WSDL

document. The page should look similar to the one below.

18. Click the Back button on the Web toolbar to move back to the HTML description page.

19. Click the hyperlink of the method of the Web Service (GetMessage) to view the method details.



20. Click the Invoke button. The Web Service will return XML output containing the results of the execution as shown below.

NOTE: If you have already a Web Site project, you can add a Web service by right-clicking on the project name in the Solutions Explorer, then clicking Add New Item to display the Add New Item window. Select Web Service in the list of templates.

[Demo: Creating a Web Service, Pages 10-14 of 14]

EVALUATION/GENERALIZATION:

• A Web service is a class that is stored on a remote machine and accessed through a remote procedure call.

• Web services method calls are implemented through SOAP.

• A Web service has two parts namely the .asmx file and the code-behind file.

• The Description property of the WebService attribute uniquely

identifies a Web service.

• A developer specifies a method as a Web service by marking it with a WebMethod attribute.

REFERENCES:

� Microsoft Official Course, (2002), 2373B: Programming with

Microsoft Visual Basic .NET, Microsoft Corporation � Holzner, Steven, (2003), Sams teach yourself Microsoft Visual

Basic.Net 2003 in 21 days, USA, Sams Publishing � Liberty, Jesse, (2003), Learning Visual Basic .NET, USA,

O'Reilly & Associates, Inc

Technology

MELJUN CORTES Vb.net handout understanding web service