Procedure 5-1. Compare the HTTP-GET and HTTP-POST message structures

1. Start Internet Explorer.

2. In the Address text field, enter the URL of the .asmx file for the VISAValidator XML Web service that we created in Chapter 3. The URL for this service is http://localhost/XMLWebServices/Chapter03/VisaValidator/Validation.asmx.

   

3. Click the ValidateVISACard link to display the help page for that operation.

4. Scroll down the Web page, past the Test and SOAP sections, until you see the HTTP GET section. You will see the structure of the HTTP-GET request required to invoke the ValidateVISACard method, followed by a sample HTTP response.

   

5. Scroll down further, and you will see the HTTP POST section. This section includes both the equivalent HTTP-POST message for invoking the ValidateVISACard method and a sample HTTP response.

   

6. Look at the sample responses in both the HTTP GET and HTTP POST sections. You will notice that they are the same for both protocols. Regardless of whether you use HTTP-GET or HTTP-POST, the XML Web service returns the same XML fragment.

   

Procedure 5-2. Copy the WebFormsClient Application

1. Use the process we described in the section "Copying Web Projects" earlier in this chapter to make a copy the WebFormsClient project you developed in Chapter 4. Copy the project to the URL http://localhost/XMLWebServices/Chapter05/WebFormsClient .

2. Close the old project, open the new one, and save the new solution file before proceeding.

3. In Solution Explorer, right-click the WebForm1.aspx file and select Set As Start Page from the shortcut menu. This step is required so that Visual Studio .NET knows which file to load when we test the application later.

Procedure 5-3. Modify the WebFormsClient Application

1. In Solution Explorer, double-click on the WebForm1.aspx entry. WebForm1 opens in design view.

   

2. In the WebForm1 design view, double-click on the Validate button.

   Visual Studio .NET opens the code view for WebForm1 and displays the ValidateButton_Click method, which executes when the user clicks the Validate button.

3. Replace the existing ValidateButton_Click method with the following code.

   Example 5-1. C#

   private void ValidateButton_Click(object sender, 
       System.EventArgs e) {
       // create the request URL
       StringBuilder x_builder = new StringBuilder();
       // add the host element of the URL
       x_builder.Append("http://localhost");
       // add the first part of the URL of the Web Service
       x_builder.Append("/XMLWebServices/Chapter03/");
       // add the second part of the URL of the Web Service
       x_builder.Append("VisaValidator/Validation.asmx");
       // add the details of the method we want to invoke
       x_builder.Append("/ValidateVISACard?");
       // add the argument name and the value we want to
       // supply for the argument
       x_builder.Append("p_card_number=" +
           CreditCardNumberText.Text);
       // create the web client and obtain the response data
       // as a byte array
       WebClient x_web_client = new WebClient();
       byte[] x_response =
           x_web_client.DownloadData(x_builder.ToString());
       // process the string result to obtain a validation result
       bool x_valid =
           processResultString(
               Encoding.Default.GetString(x_response));
       if (x_valid) {
           ResultLabel.Text = "Number Valid";
       } else {
           ResultLabel.Text = "Number Invalid";
       }
   }

   Example 5-2. Visual Basic .NET

   Private Sub ValidateButton_Click(ByVal sender As Object, _
       ByVal e As System.EventArgs) Handles ValidateButton.Click
       ‘ create the request URL
       Dim x_builder As StringBuilder = New StringBuilder()
       ‘ add the host element of the URL
       x_builder.Append("http://localhost")
       ‘ add the first part of the URL of the Web Service
       x_builder.Append("/XMLWebServices/Chapter03/")
       ‘ add the second part of the URL of the Web Service
       x_builder.Append("VisaValidator/Validation.asmx")
       ‘ add the details of the method we want to invoke
       x_builder.Append("/ValidateVISACard?")
       ‘ add the argument name and the value we want to
       ‘ supply for the argument
       x_builder.Append("p_card_number=" + CreditCardNumberText.Text)
       ‘ create the web client and obtain the response data
       ‘ as a byte array
       Dim x_web_client As WebClient = New WebClient()
       Dim x_response() As Byte = _
           x_web_client.DownloadData(x_builder.ToString())
       ‘ process the string result to obtain a validation result
       Dim x_valid As Boolean = _
           processResultString(Encoding.Default.GetString(x_response))
       If x_valid Then
           ResultLabel.Text = "Number Valid"
       Else
           ResultLabel.Text = "Number Invalid"
       End If
   End Sub

4. Add the following processResultString method as a member of the WebForm1 class.

   This method performs a simple test on the XML returned from the ValidateVISACard Web method. If the string >true</boolean> is found within the XML document, we deduce that the VISA card is valid and return true; otherwise we return false. This is not a robust approach to handling the result, but it is sufficient for the purpose of our demonstration.

   Example 5-3. C#

   private bool processResultString(string p_result) {
       if (p_result.IndexOf(">true</boolean>") > -1) {
           return true;
       } else {
           return false;
       }
   }

   Example 5-4. Visual Basic

   Private Function processResultString(ByVal p_result As String) _
       As Boolean
       If p_result.IndexOf(">true</boolean>") > -1 Then
           Return True
       Else
           Return False
       End If
   End Function

5. Scroll to the top of WebForm1 in code view and add the statements to import the namespaces of the System.Net.WebClient and System.Text.StringBuilder classes.

   Here’s how the import sections should appear:

   Example 5-5. C#

   // import the namespaces required for this example
   using System.Net;
   using System.Text;

   Example 5-6. Visual Basic .NET

   ‘ import the namespaces required for this example
   Imports System.Net
   Imports System.Text

6. Finally, press Ctrl+Shift+B or select Build Solution from the Build menu to build the solution.

Procedure 5-4. Test the WebFormsClient application

1. Press F5. Visual Studio .NET launches Internet Explorer and loads the WebFormsClient page.

2. Type a credit card number into the Card Number text field, and then click the Validate button.

   If the number is valid, you will see the message "Number Valid." If the number is invalid or incorrectly formatted, you will see the message "Number Invalid."