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This chapter is from the book

Implementing the Web Service Client

Although being able to access a Web Service from a Web browser is nice, a more realistic use is to create custom client programs that access a Web Service remotely, such as Web pages and standalone applications. To demonstrate how to create such programs, we'll create two different clients for our TimeUtils Web Service: a console application and a Web page.

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You can create Web Service clients easily by using Visual Studio.NET; we'll explain how to create them a little later. However, to show some of the "plumbing" behind Web Services, let's continue using a text editor to create our client programs.

Before creating the client to our TimeUtils application, we need to create a proxy class. A proxy class allows us to call the GetTime method without worrying about how to connect to the server and how to pass and return parameters to and from the method. In general, a proxy is an object that wraps up method calls and parameters, forwards them to a remote host, and returns the results to us. Proxies serve the role as a middleman on the client computer.

.NET comes with a special utility called WSDL.exe for creating Web Service proxies. As you might imagine from the utility's name, WSDL.exe takes a Web Service's WSDL description and creates a proxy. Follow these steps to create the proxy with WSDL.exe:

  1. Open a Visual Studio.NET command prompt (from the Start menu, choose Visual Studio.NET, Visual Studio.NET Tools, and then Visual Studio.Net Command Prompt). This DOS command prompt contains all the paths for the .NET tools.

  2. Create a new directory for the client projects, such as C:\src\timeclient.

  3. Type the following command at the prompt (try to fit the entire command at the second prompt onto one line):

    C:>cd src\timeclient
    C:\src\timeclient> wsdl /l:CS /n:WebBook
      /out:TimeProxy.cs
      http://localhost/TimeService/TimeUtils.asmx?WSDL

    This command creates the TimeProxy.cs file, which you can use in your client applications:

    • /l:CS tells the utility to create the proxy using C#.

    • /n:WebBook specifies a namespace for the WSDL tools to use when it creates the proxy class. You can use any namespace name you want.

    • /out:TimeProxy.cs specifies the name of the output file.

    • The last parameter is an URL for getting a WSDL description of the Web Service. You can also specify a file containing WSDL. However, if you use an URL, as in this example, the utility will automatically browse to the Web address and use the WSDL file that it finds.

  4. Compile the new proxy file:

    C:\src\timeclient> csc /t:libarary TimeProxy.cs

The proxy that the WSDL.exe utility creates should look like the file shown in Listing 3.

Listing 3—An Automatically Generated Proxy Class for the TimeUtils Client

 1: //-----------------------------------------------------------------------
 2: // <autogenerated>
 3: //   This code was generated by a tool.
 4: //   Runtime Version: 1.0.2914.16
 5: //
 6: //   Changes to this file may cause incorrect behavior and will be lost
 7: //   if the code is regenerated.
 8: // </autogenerated>
 9: //-----------------------------------------------------------------------
10:
11: //
12: // This source code was auto-generated by wsdl, Version=1.0.2914.16.
13: //
14: namespace WebBook {
15:   using System.Diagnostics;
16:   using System.Xml.Serialization;
17:   using System;
18:   using System.Web.Services.Protocols;
19:   using System.Web.Services;
20:
21:   [System.Web.Services.WebServiceBindingAttribute(
22:     Name="TimeUtilitiesSoap",
23:     Namespace="http://tempuri.org/webservices")]
24:   public class TimeUtilities : 
25:     System.Web.Services.Protocols.SoapHttpClientProtocol {
26:
27:     [System.Diagnostics.DebuggerStepThroughAttribute()]
28:     public TimeUtilities() {
29:       this.Url = "http://localhost/TimeService/TimeUtils.asmx";
30:     }
31:
32:     [System.Diagnostics.DebuggerStepThroughAttribute()]
33:     [System.Web.Services.Protocols.SoapDocumentMethodAttribute(
34:       "http://tempuri.org/webservices/GetTime",
35:        RequestNamespace="http://tempuri.org/webservices",
36:        ResponseNamespace="http://tempuri.org/webservices",
37:        Use=System.Web.Services.Description.SoapBindingUse.Literal,
38: ParameterStyle=System.Web.Services.Protocols.SoapParameterStyle.Wrapped)]
39:     public string GetTime() {
40:       object[] results = this.Invoke("GetTime", new object[0]);
41:       return ((string)(results[0])); 
42:     }
43:
44:     [System.Diagnostics.DebuggerStepThroughAttribute()]
45:     public System.IasyncResult
46:       BeginGetTime(System.AsyncCallback callback,
47:              object asyncState) {
48:       return this.BeginInvoke("GetTime", new object[0],
49:           callback, asyncState);
50:     }
51:
52:     [System.Diagnostics.DebuggerStepThroughAttribute()]
53:     public string EndGetTime(System.IAsyncResult asyncResult) {
54:       object[] results = this.EndInvoke(asyncResult);
55:       return ((string)(results[0]));
56:     }
57:   }
58: }

The proxy file contains a new definition for the TimeUtilities class, different from the one created earlier in Listing 1. This new definition is the version that all our client programs will use. Although this new class is defined differently than the original created for the Web Service, this new TimeUtilities class will work the same way for any client program that uses it. Rather than execute code directly, this new class will call the Web Service to execute each method.

Notice also the two new methods in the proxy class, BeginGetTime (Lines 44–50) and EndGetTime (Lines 52–56). These methods are created so that we can call the Web Service asynchronously. This means that we can call the Web Service in our client program and then do other work immediately. Then, when the Web Service returns a result, we can process the results at that time. This asynchronous method for calling remote Web Services might not be responsive because of a slow network connection.

Now that we've created our proxy class, we can create client programs that use our Web Service. To begin, let's create a simple console application to call the Web Service. The client is shown in Listing 4.

Listing 4—CallService.cs: A Console Application That Calls the TimeUtils Web Service

using System; 
using WebBook;

namespace WebBook
{
 public class CallService
 {
  public static void Main()
  {
   TimeUtilities remoteService = new TimeUtilities();

   Console.WriteLine("Calling web service...");

   Console.WriteLine(remoteService.GetTime());
  }
 }
}

If you save the CallService.cs client in the TimeClient project directory that you created, you can compile it by using this command:

csc CallService.cs /r:TimeProxy.dll

This command creates a file named CallService.exe in the client directory, which you can run now. For this command to work, you must have compiled the proxy class in Listing 3 according to the instructions in step 4 of this section.

After running the CallService.exe program you created, you should see output like the following:

Calling web service...
The current time on the server is: 7/9/2001 12:19:08 PM

Creating a Web Service Client

Now that you've seen how to create a Web Service proxy and client program manually, let's use Visual Studio.NET to make a Web page that calls the TimeUtils Web Service. Visual Studio.NET automates the process by creating a proxy file using a wizard. For the example in this section, we'll create an ASP.NET page that calls the Web Service.

To create the client application, follow these steps:

  1. Create a new ASP.NET Web application by selecting New Project on Visual Studio's start page.

  2. In the New Project dialog, select Visual C# Projects in the Project Types list and then select ASP.NET Web Application from the Templates list. Name the Web application ASPClient and click OK (see Figure 3).

    Figure 3 The New Project dialog.

  3. From the Project menu, choose Add Web Reference. You should see a dialog similar to Figure 4.

    Figure 4 The Add Web Reference dialog.

  4. In the Address text box, enter http://localhost/TimeService/TimeUtils.asmx and then click the Add Reference button to create a proxy file for the Web Service and add it to your project.

  5. Change the Page_Load method in WebForm1.aspx to use the code in Listing 5.

  6. Run the project.

Listing 5—Page_Load Method for the Visual Studio Client ASP.NET Page

private void Page_Load(object sender, System.EventArgs e)
{
  localhost.TimeUtilities remoteService = new localhost.TimeUtilities();
  Response.Write(remoteService.GetTime());
}

If the remote Web Service resides on another machine, the localhost string in Listing 5 changes to the name of that machine. After running the project, you should see a screen similar to Figure 5.

Figure 5 The ASP.NET client for the Web Service.

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