11 Web Services. 22 Objectives You will be able to Say what a web service is. Write and deploy a simple web service. Test a simple web service. Write.

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Web Services

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Objectives

You will be able to Say what a web service is. Write and deploy a simple web

service. Test a simple web service. Write a client program for a simple

web service.

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What are Web Services?

Make web apps available to programs Like they are available to human users via

web browsers.

Use HTTP SOAP XML

Motivation: Platform independence

Drawback High communication overhead

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Web Service Frameworks

Version 3.5 of the .NET Framework provides two quite different ways to develop web services:

ASP.NET Web Services The traditional approach

Windows Communications Foundation New in .NET 3.5 and Visual Studio 2008

Visual Studio 2010 supports both methods. We will follow the traditional approach.

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What is a .NET Web Service?

Web Services in the .NET environment A form of remote method invocation (RMI) Layered on top of basic message based web

service protocol. SOAP Simple Object Access Protocol

Motivation: Method invocation is familiar to programmers. No need to understand the SOAP protocol. No need to work directly with messages.

This is the only form of web service that we will study.

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How do RMI Web Services Work?

Client code invokes “proxy” method on own system. Same interface as the remote method

Proxy prepares a SOAP message encoding identification of function and arguments.

Proxy sends message to web server on remote system.

Web server on remote system parses the SOAP message and invokes the specified method.

Web server sends result back as a SOAP message. Proxy on client system parses message and

delivers result.

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How do RMI Web Services Work?

The interface seen by the client program is the same as if the method were local.

But don't be deceived! There is a round trip message exchange before

the remote function returns. MUCH slower than a local function.

Good web services do a lot of work on a single method invocation.

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How do web services work?

When using ASP.NET and Visual Studio Library functions handle most of the work. It is not necessary to understand the SOAP

protocol or message coding.

Let’s try a simple example: Hello Service A service that returns the message “Hello,

world!” whenever it is invoked.

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Creating a Web Service

In Visual Studio 2010, create a new web site using the Web Service template. Note: New web site, not new project. Location: File System Language: C# Template: ASP.NET Web Service

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New Web Site

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Creating a Web Service

In the New Web Site box Select .NET Framework 3.5

NOT 4.0 Installed Templates: Visual C# ASP.NET Web Service Name: Hello_Service

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Creating a Web Service

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Creating a Web Service

Visual Studio creates Web site with the name Hello_Service. The name specified for the web site

Containing folders App_Code and App_Data Initial source code file called Service.asmx

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The “Service”

Will be visible on the Internet when deployed to a Microsoft web server. Processed by the Microsoft Web Server (IIS) like .aspx files.

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Initial Code for Our Web Service

A very simple example provided by Visual Studio.

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Initial Code for Our Web Service

Note the class name, “Service”. Also the name of the .asmx file

Can be any name we wish. “Service” is just the default.

Let’s change the class name to “Hello_Service”

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Create New Web Site

Change file names from Service to Hello_Service Hello_Service.asmx App_Code\Hello_Service.cs

In Hello_Service.cs Change name of class from Service to

Hello_Service Also constructor

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Rename the .asmx File

Update CodeBehind file name and Class name.

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Set Port Number

In Solution Explorer Select Project

Main Menu > View > Properties Window

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Set Port Number

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Set Port Number

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Set Port Number

In the Properties Window Set Use dynamic ports to false. Set Port number to 4500

An arbitrary choice

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Set Port Number

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Class “Hello_Service"

Examine class Hello_Service

Derived from System.Web.Services.WebService

Note attributes (in square brackets) Compiler directives Method HelloWorld has attribute [WebMethod]

Any method to be provided to remote clients must have attribute [WebMethod]

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Attributes of Class “Hello_Service"

[WebServiceBinding(...) ] Identifies the level of web services

interoperability that this web service will conform to.

Leave at default setting

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Attributes of Class "Service"

[WebService( Namespace = ...) ] specifies a namespace to uniquely identify the web service.

Set your Namespace to your URL For example, in my case,

http://cis4930wp.eng.usf.edu/wpusr40

This is just an easy way to define a name that will be unique over the entire Internet.

There is no significance to the specific choice.

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Hello_Service Class Definition

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HelloWorld()

Normally you would delete the HelloWorld() method and enter your own methods in its place.

For this first example, we will leave it. Define a web method called

HelloWorld() which will return the string “Hello World” to any client that invokes the service.

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Build the Service

Now build the service

Main Menu > Build > Build Web Site

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Testing the Service

How do we test the service? It needs a client!

Browsers provide a default client that we can use to test a service running on Visual Studio. Right click on Hello_Service.asmx in the

Solution Explorer window. Select View in Browser.

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Testing the Service

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Testing the Service in Chrome

Click here

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Testing the Service in Chrome

Click here

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Here is the Result

Click the first tab to return, then click the “Back” button.

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Service Description

Click here

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Service Description - WSDL

End of Section

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WSDL

Web Services Description Language

A web service must be able to provide a detailed specification of its interface upon request.

Permits the client to construct a SOAP message in the correct format for this service.

Visual Studio handles this transparently when we use it to write client software.

Click the browser's back button to return to the web service page and leave it running.

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Consuming a Web Service

Now let’s write a client app to use the HelloWorld web service. Leave this web service running.

Clients can be either PC programs or web apps Including other web services.

Since this is a web apps class, let's write a web app to use the Hello_Service.

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Consuming a Web Service

We will need a proxy Presents same appearance to the client

program as the remote method Communicates with the web server

using SOAP messages. Passes result to client program as if the

method had been executed locally.

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Consuming a Web Service

Start up another instance of Visual Studio 2010.

First instance must continue running to support the service.

Create a new C# ASPX.NET Web Site Call it Test_Hello.

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Creating a Client App

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Creating a Client App

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Creating a Client App

Let the test app have a button to invoke the HelloService web method.

A label to display the result.

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Design the Form

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Add Reference to the Web Service

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Get URL of the Running Web Service

Select and copy URL from address box

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Paste in URL for the web service. (Or type it.) Then click .

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Adding a Web Reference

Browsing won’t work when the service is running in Visual Studio’s built in web server.

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Adding a Web Reference

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Adding a Web Reference

Fill in a Web reference name. Than click “Add Reference”.

The name is your choice, but should be meaningful.

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Adding a Web Reference

Visual Studio contacts the web site that we identified. Doesn't have to be on the same computer as

it is in this case. Could be anywhere.

Visual Studio gets the WSDL Web Service Specification from the web service.

Using the WSDL spec, Visual Studio creates the proxy and makes it a part of our website.

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Check the Solution Explorer

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Recall the Service Definition

The class that provides the HelloWorld remote method is called “Hello_Service”.

HelloWorld is a method of class “Hello_Service”.

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Using the Web Service

We have to instantiate the Hello_Service class.

Then invoke its HelloWorld method.

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Open Code Window in Test Program

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Include the Web Reference Name in "Usings"

At the top, add using Hello_Service_on_localhost;

The web reference that we added to the application

This is the namespace in which the proxy class exists.

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Default.aspx.cs with new “using”

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Add an Event Handler

Back in Design window

Double click on the "Invoke HelloWorld" button, to generate an event handler for it.

Fill in code as shown on the next slide

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Event Handler

private void btnInvokeHello_Click(object sender, EventArgs e)

{

Hello_Service hs = new Hello_Service();

try

{

lblResult.Text = hs.HelloWorld();

}

catch (Exception ex)

{

lblResult.Text = ex.Message;

}

}

The proxy class generated when we added the web reference

The specific method to invoke within the web service.

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Try it!

Build and run the test app.

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Here is our result.

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Summary: Creating a Web Service Client

Know the URL and Interface definition for the web service.

Create a normal web application (or PC application).

Add a web reference. Specify URL of the web service. This adds a proxy class to the project. Proxy class interface is identical to that of the

web service. Add “using” statement for the web reference. Instantiate the web service class. Invoke methods of the web service as if it were a

local class.End of Presentation