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Building Web Services Using Microsoft .NET
Building Web Services Using Microsoft .NET
By: Jonathan Cortez
Jan. 1, 2000 12:00 AM
Microsoft .NET is the key enabling technology for Microsoft's vision of software as a service. The .NET Framework is the overall infrastructure that provides developers with a platform to create programs that transcend device boundaries and fully harness the connectivity of the Internet.
In this article, I'll illustrate how easy it is to build and use Web services using the .NET Framework SDK. I used the Beta 2 of the .NET Framework SDK and wrote all code samples using C#, Microsoft's new programming language for .NET. This article assumes you have some familiarity with Web services concepts and component-based programming. While I've tried my best to ensure that the technical content of this article is up-to-date, some features and operations in the .NET Framework might change when a newer version of the SDK ships. To try out the source code in this article, you need to download and install the Microsoft .NET Framework SDK Beta 2 from www.microsoft.com/net/downloads.asp. The SDK includes everything developers need to write, build, test, and deploy .NET Framework applications - documentation, tools, compilers, and samples. You don't need to use Visual Studio .NET to run the code samples in this article. I installed the SDK on my Windows 2000 server machine and used Notepad as my source code editor.
.NET Framework Overview
As you can see in Figure 1, the .NET Framework is essentially a system application running on top of the operating system, which can be different flavors of Windows and even other operating systems.
The most important component of the .NET Framework is the Common Language Runtime (CLR). The CLR is a rich runtime environment that provides important system services to .NET objects written in any language that can be represented in the Common Intermediate Language (CIL). The CLR activates objects, performs code access security, lays out objects in memory, verifies type safety, performs garbage collection, and facilitates error handling. Java developers may think of the CLR as the .NET equivalent of the Java Virtual Machine (VM).
Sitting on top of the CLR is the Base Class Library, consisting of classes that support IO functions, string manip-ulation, security management, threading, reflection function-ality, collections, and other functions.
On top of the base class library is a set of classes that provide data and XML manipulation. ADO. NET and SQL classes allow you to access and manipulate persistent data stored on backend databases. The framework also provides a number of classes to manipulate XML, perform XML searches, and perform XML transformations.
Win Forms (or Windows Forms) provides classes for development of native Windows GUI applications. If you've developed MFC applications in the past, you'll fall in love with Win Forms since it supports easier GUI development and provides a common and consistent interface across all languages. ASP.NET is the Web application platform that enables developers to easily develop both powerful Web services and use Web Forms to build rich browser-based applications.
Web Services in ASP.NET
ASP.NETWeb Services is a technology that allows you to build and expose Web services. Since ASP.NET Web Services are built on top of ASP.NET, you can take advantage of the features of ASP.NET such as caching, state management, and authentication, which are all built into the framework. Also, all ASP.NET codes are compiled rather than interpreted, which offers significant performance improve-ments over the current Active Server Pages (ASP) programming model.
ASP.NET Web Service Clients pertains to any components or applications that reference and make use of a Web service. This reference is made possible through a proxy class for the Web service.
In the following sections, I'll show you how to build and consume a Web service using ASP.NET.
Building a .NET Web Service
Declare the Web service
The class implementing the Web service doesn't need to reside on the same .asmx file. You can achieve a higher degree of code reusability by placing the implementing class in an assembly. Your .asmx file will contain only the WebService directive, and the assembly needs to reside under the \bin directory of the Web application hosting the Web service. This is illustrated in Listing 2. MyAssembly.cs is compiled with the C# compiler (csc.exe) to MyAssembly.dll using the following command:
csc /t:library MyAssembly.cs
In the WebService directive in Listing 2, the implementing class name and the assembly name are both specified. If the assembly name is not specified, ASP.NET searches through the list of assemblies in the \bin directory of the Web application the first time the Web service is accessed. Therefore, specifying the assembly name will yield better performance on the first access of the Web service.
Classes implementing Web services can optionally derive from the WebService class of the System.Web.Services namespace. This will allow your implementing class to have access to all the common ASP.NET objects such as Application and Session objects. These common ASP.NET objects can be accessed via the Context property of the WebService class.
Your Web service, by default, will use the XML namespace http://tempuri.org/. I would highly recommend that you specify your own namespace for your Web service before it is made available publicly. To do this, apply the optional WebService attribute to the class implementing your Web service and specify your own namespace in the Namespace attribute. This will distinguish your Web service from other Web services that might be using the default namespace. The code example in Listing 3 illustrates overriding the default XML namespace by specifying a custom XML namespace.
Define the Web Service Methods
I created a sample Web service that provides basic mathematical functions such as Addition, Subtraction, Multiplication, and Division (see Listing 5). The Web service resides in a file called Calculator.asmx. To set up the Web service on my local box, I used IIS 5.0 Internet Services Manager to create a virtual directory called WebServices. I placed the Calculator.asmx file on that directory. The complete URL to this Calculator Web service is http://localhost/ WebServices/Calculator.asmx. If you deploy this sample Web service on a remote server, you'll need to substitute the name of the server and the virtual directory appropriately.
Consuming a .NET Web Service
Default Web Service Consumer
If we try invoking the Add method with 1 and 2 as input parameters, a new browser window is displayed containing the XML-encoded result shown in Figure 4. In this example, the complete URL used to invoke the Add Web method, along with parameters, is the following: http://localhost/WebServices/Calculator.asmx/Add?lNum1=1&lNum2=2.
The default consumer also provides the description of how to access the method via SOAP, HTTP GET and HTTP POST. These descriptions help developers understand the encoding of the request and response messages, which is often critical when interoperating with a non-.NET Web service consumer.
Web Services Description Language Tool
When you create a proxy class using Wsdl.exe, the default protocol is SOAP. SOAP provides the richest extensibility mechanism of the three protocols supported by ASP.NET in the current release by allowing scenarios where classes and structs can be passed as arguments to the methods of the Web service. If you want to generate client proxy code for the Calculator Web service in the C# language and use the SOAP protocol, you'll need to execute the following in the command line:
wsdl /l:CS /o:CalculatorProxy.cs
This command will generate a C# source file called CalculatorProxy.cs containing a proxy class, Calculator, that derives from the SoapHttpClientProtocol class.
The /protocol: parameter specifies which protocol you want to use. Since SOAP is the default protocol used by Wsdl.exe, you can omit the /protocol: parameter from the above call to Wsdl.exe. If you want to use the HTTP GET protocol, specify HttpGet. The proxy class generated will derive from the HttpGetClient Protocol class. If you want to use the HTTP POST protocol, you need to specify HttpPost and the proxy class generated will derive from the HttpPostClientProtocol class.
Inspecting the generated proxy class, it includes methods that forward calls to the original Web service methods. You have two choices for how this proxy can be used in your client application. The first option is to include this source file in the client application project. However, the client application project needs to be a C# project. You also need to add into your project any references that the proxy depends on.
A better option for using the proxy class is to compile the C# proxy source file into a dynamic link library (DLL) and then add a reference to this DLL to any client project you want to create. This way, your proxy DLL is self-contained and can be used by different projects implemented in different .NET languages. Below is the command line for compiling the C# proxy source into a DLL (Calculator Proxy.dll):
csc /t:library /r:system.web.services.dll
Now let's look at the client application code that will use this proxy DLL (see Listing 6). You compile the client code to a console program (CalculatorClient.exe) using the following command line:
csc CalculatorClient.cs /r:CalculatorProxy.dll
No matter how you choose to use the proxy class, the client code will still look the same. First, an instance of the proxy class is created. Then, the appropriate methods of the proxy class are called that will in turn invoke the Web service methods. In this case, the Multiply method was invoked, passing in the value of 4 for both parameters. The resulting value was displayed on the console screen. You should see the following if you run CalculatorClient .exe from the command line:
4 X 4 = 16
That's all there is to it. Both the proxy class and the .NET Framework do all the dirty work of creating and parsing SOAP messages between the Web service and the client application.
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