Locating a Web Service with a Discovery Document

To use a discovery document to locate Web services, you need the URL for the discovery document that describes the services in which you’re interested. You might get the URL for the document from a listing on an organization’s public Web site, from an e-mail promotion, or from a catalog.

Once you have the URL for a discovery document, you can use the disco.exe command line utility to generate WSDL contracts for using the Web services described in the discovery document. The syntax for the disco.exe utility is

disco [options] URL

Here, options represents one or more command-line options for the utility, and URL represents the URL to the discovery document. Table 11-2 shows options for the disco.exe utility.

Locating a Web Service with UDDI

Unlike using a discovery document to locate a Web service, UDDI does not require you to know in advance the URL of a document describing the desired Web service. Any provider of a UDDI business registry usually will provide a tool for searching their instance of the registry for businesses or Web services that meet your needs. The criteria you can search on will depend on the organization hosting that instance. For example, Microsoft’s UDDI registry at http://uddi.microsoft.com supports searching by business name, business location, discovery URL, keyword, and a variety of other criteria. The following illustration shows the list of available criteria for searching the Microsoft UDDI registry.

One effective technique for searching for Web services on the http://uddi.microsoft.com registry is to search by discovery URL and search for URLs that contain “wsdl.” These URLs are the most likely to point to live WSDL contracts that you can use to access available Web services.

Using the wsdl.exe Utility

The wsdl.exe utility generates a proxy class in C#, Visual Basic .NET, or JScript .NET for a WSDL contract specified by URL or path. This proxy class can be instantiated and its methods called by any client, just like any other .NET class. Visual Studio .NET provides an easier way to generate a proxy class, which the next example will cover. However, at times (especially when you have special requirements not met by the standard proxy classes) you might find it handy to manually create the proxy class.

The syntax for the wsdl.exe utility is as follows:

wsdl [options] {URL | path}

Here, options represents one or more command-line options for the utility, and URL represents the URL to the WSDL contract. Alternatively, a file path to the WSDL contract can be passed as the path argument. Table 11-3 shows options for the wsdl.exe utility.

Take the following steps to create proxy classes in Visual C# .NET for the HelloService and AuthorsService example Web services created earlier in this chapter.

Create proxy classes

1. Open a command line and navigate to the directory where you would like the proxy classes to be generated. (Or use the /o option to specify a path and filename for saving the proxy class.)

2. Execute the wsdl.exe utility, using the /l option to specify Visual C# .NET as the language and passing the URL to the HelloService.asmx file, including the ?WSDL parameter, which tells ASP.NET to return the WSDL contract for the .asmx file. (Both of the following lines should form a single command.) The URL you specify should match the location of the .asmx file on your Web server, and it might differ from the following URL.

   wsdl /l:cs /n:ASPNETSBS_CS http://localhost/Chapter11/Service1.asmx?WSDL

3. Execute the wsdl.exe utility again for AuthorsService.asmx, using the same syntax as shown in step 2 but modifying the URL to point to AuthorsService.asmx.

4. Optionally, you can create a batch file (with the .bat extension) containing both of the preceding commands. If you want to see the results of the batch execution before the command window closes, add a pause command at the end of the batch file. A batch file similar to this is included in the practice files for this chapter.

Once you’ve created your proxy class, you’ll need to compile the class using the command-line compiler for the language you chose to generate (in this example, Visual C# .NET). The following listing, MakeServices.bat, shows the command-line compiler syntax to compile these classes and output the resulting assembly to the bin subdirectory of the directory from which the command is run. For this example, this should be the bin subdirectory of the Chapter_11 project. Note that this listing represents a single command and has been wrapped to multiple lines for readability. A batch file similar to this is included in the practice files for this chapter.

Consume a Web service from Visual Studio .NET

1. Open the project for this chapter, Chapter_11, in Visual Studio .NET if it is not already open.

2. Right-click on the root of the project in the Solution Explorer, and select Add Web Reference from the drop-down menu. The Add Web Reference dialog box will appear, as shown in the following illustration.

   

3. Type the URL to the AuthorsService.asmx file (if you followed the directions in this chapter, this should be http://localhost/Chapter_11/ AuthorsService.asmx) in the address text box, and click Go (you can also click Web Services On The Local Machine to browse for all local Web services, then select the AuthorsService service). The result should look similar to the illustration on the next page.

   

4. Click the Add Reference button at the bottom right-hand corner of the Add Web Reference dialog box. When the Add Web Reference dialog box closes, look in the Solution Explorer to find a new node named Web References. Under Web References, you’ll see a node added called localhost (assuming the URL entered in Step 2 was on the localhost domain). Expand that node (you might need to click the Show All Files button in the Solution Explorer toolbar first). The result should look similar to the following illustration.

   

5. Right-click on localhost, and select Rename from the drop-down menu. Rename localhost to Authors.

   When you add a Web reference, Visual Studio .NET creates a folder with the same name as the Web reference under the Web References folder that is under the main project folder. There are several files created by Visual Studio .NET in this folder. Most interesting is Reference.cs (which is hidden by default), which contains the proxy code generated by Visual Studio for accessing the Web service.

6. Add a new Web Form. Type the name of the new Web Form as ShowAuthors.aspx.

7. Click and drag a DataGrid control from the toolbox to the surface of the page of ShowAuthors.aspx.

8. Press F7 to change to code view. Scroll down to the Page_Load method, and then modify it so that it looks like the following code:

   private void Page_Load(object sender, System.EventArgs e  DataSet ds Authors.AuthorsService svc = new Authors.AuthorsService() ds = svc.GetAuthors() DataGrid1.DataSource = ds.Tables["Authors"] DataBind() }

9. Save and build the project.

10. Browse ShowAuthors.aspx using Internet Explorer. The output should look similar to the following illustration.

    

One important thing to notice about this example is that while the table we are displaying is a Microsoft SQL Server table, we do not reference System.Data.SqlClient. We don’t have to because this application is not directly connecting to a SQL Server database. Rather, the application connects to the Web service created earlier (which returns a generic DataSet), and from there the Web service itself connects to SQL Server. Because the project already contains a reference to the System.Data namespace (which is added by default to all new projects), we don’t need to add any additional namespace references to use the dataset returned from the Web service.