9.5.1 Problem You want to be able to read application information from a web.config file that is not available as an <appSettings> key / value pair, but present as an attribute or child element of some other element of the file. 9.5.2 Solution Read the web.config file into an XmlDocument object, and access the target element that contains the information you need as you would any other XML document node. In the code-behind class for your ASP.NET page, use the .NET language of your choice to: -
Read the web.config file into an XmlDocument object. -
Use the SelectSingleNode method to get a reference to the desired section. -
Use the attributes collection of the selected node to access the attributes for the section. Example 9-6 through Example 9-8 show an application we've written that implements this solution and retrieves attribute settings from the <trace> element of a web.config file. Example 9-6 shows the .aspx file that displays the information. Example 9-7 (VB) and Example 9-8 (C#) show the code-behind class for the page that does the work of reading the settings from the <trace> element. 9.5.3 Discussion Because the web.config file is an XML document, you can process it as you would any other XML document and use the XML classes provided in the .NET Framework to access its elements and their children. The first step is to create a new XmlDocument object and load the web.config file into it. In our example, we use Server.MapPath to get the fully qualified name for the web.config file: xmlDoc = New XmlDocument xmlDoc.Load(Server.MapPath("web.config")) xmlDoc = new XmlDocument( ); xmlDoc.Load(Server.MapPath("web.config"));
Next, use the SelectSingleNode method, passing it the fully qualified path from the root of the XML document to the desired section of the web.config file. In our application, for example, we want to access the <trace> section: xmlNode = xmlDoc.SelectSingleNode("configuration/system.web/trace") xmlNode = xmlDoc.SelectSingleNode("configuration/system.web/trace");
 | XML is case-sensitive, and node names are separated by using a forward slash (/). | |
After getting a reference to the desired section (or node in XML terminology), the attributes collection of the node, which contains all of the attribute information for the requested web.config section, is available. In our example, we use the GetNamedItem method of the attributes collection to access the specific attributes whose values we want. If you need to display all of the attributes from a section, you can iterate through the attributes collection using the name and value properties of each attribute to read and then output the information. The approach described in this recipe can provide access to the attributes of any element in the web.config file. And, as a bonus, you can use the same method to programmatically change any of those attributes. The following code, for example, changes the value of the enabled attribute of <trace> to true and then saves the web.config file with the new value. When the file is saved, ASP.NET, which monitors the web.config file for changes, restarts the application. attributes.GetNamedItem("enabled").Value = "true" xmlDoc.Save(Server.MapPath("web.config")) attributes.GetNamedItem("enabled").Value = "true"; xmlDoc.Save(Server.MapPath("web.config"));
Example 9-6. Access system configuration information in web.config (.aspx) <%@ Page Language="vb" AutoEventWireup="false" Codebehind="CH09AccessSystemConfigVB.aspx.vb" Inherits="ASPNetCookbook.VBExamples.CH09AccessSystemConfigVB"%> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <html> <head> <title>Accessing System Configuration Information</title> <link rel="stylesheet" href="css/ASPNetCookbook.css"> </head> <body leftmargin="0" marginheight="0" marginwidth="0" topmargin="0"> <form id="frmConfiguration" method="post" runat="server"> <table width="100%" cellpadding ="0" cellspacing="0" border="0"> <tr> <td align="center"> <img src="images/ASPNETCookbookHeading_blue.gif"> </td> </tr> <tr> <td class="dividerLine"> <img src="images/spacer.gif" height="6" border="0"></td> </tr> </table> <table width="90%" align="center" border="0"> <tr> <td><img src="images/spacer.gif" height="10" border="0"></td> </tr> <tr> <td align="center" class="PageHeading"> Accessing System Configuration Information In web.config (VB) </td> </tr> <tr> <td><img src="images/spacer.gif" height="10" border="0"></td> </tr> <tr> <td align="center"> <table width="40%"> <tr> <td align="center" class="SubHeading" colspan="2"> trace Section Attributes </td> </tr> <tr> <td align="right" width="50%" class="LabelText">enabled = </td> <td width="50%" class="LabelText"> <asp:Label ID="labEnabled" runat="server" /> </td> </tr> <tr> <td align="right" class="LabelText">requestLimit = </td> <td class="LabelText"> <asp:Label ID="labRequestLimit" runat="server" /> </td> </tr> <tr> <td align="right" class="LabelText">pageOutput = </td> <td class="LabelText"> <asp:Label ID="labPageOutput" runat="server" /> </td> </tr> <tr> <td align="right" class="LabelText">traceMode = </td> <td class="LabelText"> <asp:Label ID="labTraceMode" runat="server" /> </td> </tr> <tr> <td align="right" class="LabelText">localOnly = </td> <td class="LabelText"> <asp:Label ID="labLocalOnly" runat ="server" /> </td> </tr> </table> </td> </tr> </table> </form> </body> </html>
Example 9-7. Access system configuration information in web.config code-behind (.vb) Option Explicit On Option Strict On '----------------------------------------------------------------------------- ' ' Module Name: CH09AccessSystemConfigVB.aspx.vb ' ' Description: This module provides the code behind for the ' CH09AccessSystemConfigVB.aspx page ' '***************************************************************************** Imports Microsoft.VisualBasic Imports System Imports System.Xml Namespace ASPNetCookbook.VBExamples Public Class CH09AccessSystemConfigVB Inherits System.Web.UI.Page 'controls on the form Protected labEnabled As System.Web.UI.WebControls.Label Protected labRequestLimit As System.Web.UI.WebControls.Label Protected labPageOutput As System.Web.UI.WebControls.Label Protected labTraceMode As System.Web.UI.WebControls.Label Protected labLocalOnly As System.Web.UI.WebControls.Label '************************************************************************* ' ' ROUTINE: Page_Load ' ' DESCRIPTION: This routine provides the event handler for the page load ' event. It is responsible for initializing the controls ' on the page. '------------------------------------------------------------------------- Private Sub Page_Load(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles MyBase.Load Dim xmlDoc As XmlDocument Dim xmlNode As XmlNode Dim attributes As XmlAttributeCollection 'load web.config xmlDoc = New XmlDocument xmlDoc.Load(Server.MapPath("web.config")) 'get the trace section xmlNode = xmlDoc.SelectSingleNode("configuration/system.web/trace") If (Not IsNothing(xmlNode)) Then 'the trace section is a collection or attributes so get the 'collection then output the individual values attributes = xmlNode.Attributes labEnabled.Text = attributes.GetNamedItem("enabled").Value labRequestLimit.Text = attributes.GetNamedItem("requestLimit").Value labPageOutput.Text = attributes.GetNamedItem("pageOutput").Value labTraceMode.Text = attributes.GetNamedItem("traceMode").Value labLocalOnly.Text = attributes.GetNamedItem("localOnly").Value End If End Sub 'Page_Load End Class 'CH09AccessSystemConfigVB End Namespace
Example 9-8. Access system configuration information in web.config code-behind (.cs) //---------------------------------------------------------------------------- // // Module Name: CH09AccessSystemConfigCS.aspx.cs // // Description: This module provides the code behind for the // CH09AccessSystemConfigCS.aspx page // //**************************************************************************** using System; using System.Xml; namespace ASPNetCookbook.CSExamples { public class CH09AccessSystemConfigCS : System.Web.UI.Page { // controls on the form protected System.Web.UI.WebControls.Label labEnabled; protected System.Web.UI.WebControls.Label labRequestLimit; protected System.Web.UI.WebControls.Label labPageOutput; protected System.Web.UI.WebControls.Label labTraceMode; protected System.Web.UI.WebControls.Label labLocalOnly; //************************************************************************ // // ROUTINE: Page_Load // // DESCRIPTION: This routine provides the event handler for the page // load event. It is responsible for initializing the // controls on the page. //------------------------------------------------------------------------ private void Page_Load(object sender, System.EventArgs e) { XmlDocument xmlDoc = null; XmlNode xmlNode = null; XmlAttributeCollection attributes = null; // load web.config xmlDoc = new XmlDocument( ); xmlDoc.Load(Server.MapPath("web.config")); // get the trace section xmlNode = xmlDoc.SelectSingleNode("configuration/system.web/trace"); if (xmlNode != null) { // the trace section is a collection of attributes so get the attributes = xmlNode.Attributes; labEnabled.Text = attributes.GetNamedItem("enabled").Value; labRequestLimit.Text = attributes.GetNamedItem("requestLimit").Value; labPageOutput.Text = attributes.GetNamedItem("pageOutput").Value; labTraceMode.Text = attributes.GetNamedItem("traceMode").Value; labLocalOnly.Text = attributes.GetNamedItem("localOnly").Value; } } // Page_Load } // CH09AccessSystemConfigCS }
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