Introduction

In this, we tell you why Web Services are an important new development in the area of Internet standards, and what business problems they address.

We talk about the Simple Object Access Protocol (SOAP), which lets you exchange data and documents over the Internet in a well-defined way, and related standards to describe and discover Web Services. Finally, we cover techniques for error handling and state management and discuss how Web Services integrate with the Microsoft .NET platform.

The Role of SOAP

SOAP stands for Simple Object Access Protocol. SOAP was designed with the following three goals in mind:

It should be optimized to run on the Internet.
It should be simple and easy to implement.
It should be based on XML.

SOAP, somewhat contrary to its name, is fundamentally just a protocol that lets two systems: a client and a server exchange data. Of course, the client system may be, and often is, just another server machine, not a human end user.

Creating Your Very First Web Service

Let us look at a SOAP exchange between a client and a server by way of a few examples. Although Web Services are most interesting when used to couple server computers, our examples are more geared towards end users interacting with a Web Service server; we only do this to keep the examples reasonably simple and self contained.

As mentioned earlier, we look only at SOAP as implemented over the HTTP protocol. Also, we initially focus on SOAP as an RPC mechanism. In this, when we discuss the development of a more comprehensive Web Service, you will encounter SOAP used to interchange complex XML documents. Let us start by setting up a simple echo Web Service.This service simply returns whatever character string a user submits.

Creating a class that echoes its input is fairly straightforward, of course

Echo Method
namespace soapExamples
{
     public class simpleService
{
     public simpleService()
{
}
     public string echo(string input)
{
     return input;

}}}

How can you now make this into a Web Service? In other words, what is needed to make this method accessible to everybody in the world who has an Internet connection and knows where to find your method?

It may be hard to believe initially, but all that is needed using the .NET Framework is apart from an Internet Information Server (IIS) Web server, of course two tiny little changes:

Your class simpleService needs to inherit from System.Web.Services.WebService.

Your method echo needs to be decorated with the System.Web.Services.WebMethod attribute.

See echo web method for your first fully functioning Web Service.

Echo Web Method (simpleService.asmx.cs)

namespace soapExamples

{

public class simpleService : System.Web.Services.WebService

{

public simpleService() {www.syngress.com}

protected override void Dispose( bool disposing )
{
}

[System.Web.Services.WebMethod]

public string echo(string input)
{

return input;

}

}
}

Let us now open up the Visual Studio.NET integrated development environment and create the echo Web Service from scratch, proceeding as follows:

Create a new ASP.NET Web Service called soapExamples:

Go to File | New | Project, choose the entry ASP.NET Web Service under the Visual C# Projects folder, keep the default Location, and enter soapExamples as the Name of the project (see Figure ).This will set up a new virtual directory of the same name (see Figure).

Visual Studio.NET Automatically Sets Up a New Web

Visual Studio.NET will then configure the necessary FrontPage server extensions, define an assembly, and create supporting project files for you. Annoyingly, the wizard also creates a default Web Service file called Service1.asmx, which you may remove in the Solution Explorer by right-clicking on the file and selecting Delete.Or, you can simply rename that file to simpleService.asmx in the Solution Explorer and proceed with next step.
Now you create your actual Web Service: Right-click on the soapExamples project in the Solution Explorer, and choose Add | Add New Item. Choose Web Service from the list of available templates, and call it simpleService.asmx (see Figure).

Creating a New Web Service

Select the Web Service simpleService.asmx in the Solution Explorer, and click on the little View Code icon to see the code for this Web Service added by the wizard.
Replace the code with the code for this class shown in Figure.
The last step is the most remarkable step if you have been used to traditional ASP developing. Compile your project: select Build | Build from the User menu, or press Ctrl+Shift+B. In other words,ASP.NET applications, such as a Web Service application, are compiled applications (and yes, it will create a .NET DLL for you)

Table for Files Created by Visual Studio.NET for soapExamples Web Service