In this article I am going to share some techniques on globally trapping and handling errors that occur in a web application and then how to notify administrators/developers that the error has occurred. I will use the Application_OnError subroutine of the global.asax file to trap the errors and then the aspNetEmail component to send the error notification e-mails.[bold]Introduction[/bold]When porting our campus? student information portal to ASP.NET, we realized that the previous ASP ...In this article I am going to share some techniques on globally trapping and handling errors that occur in a web application and then how to notify administrators/developers that the error has occurred. I will use the Application_OnError subroutine of the global.asax file to trap the errors and then the aspNetEmail component to send the error notification e-mails.[bold]Introduction[/bold]When porting our campus? student information portal to ASP.NET, we realized that the previous ASP version generated many errors that we had no idea had occurred. It was decided that in the new version we needed some way to trap errors and then e-mail us information about the error.We didn?t want to use System.Web.Mail because our administrators did not want to install SMTP server on all of our web servers. After looking around a bit, we decided to go with the aspNetEmail component, which in addition to allowing us to use our single campus SMTP server, also allowed for us to dynamically create the HTML error e-mails and include DataGrids.[bold]Error Trapping[/bold]Error trapping and handling at an application level is super easy to do in ASP.NET. All errors occur at the application level, so you can trap errors using the Application_OnError method of global.asax.In our Application_OnError subroutine, we grab the exception for the error using Context.Error.GetBaseException() as seen in the code below:
Sub Application_Error
(ByVal sender As Object, ByVal e As EventArgs)
Dim ex As Exception = Context.Error.GetBaseException()
Dim objErrHandler As New ErrorHandler()
objErrHandler.SendHtmlErrorEmail(ex)
End Sub
After the exception is grabbed, it is passed to the SendHtmlErrorEmail function of the ErrorHandler class, which does the work of generating the e-mail.[bold]Collecting additional information[/bold]In addition to being sent information about the error itself, we also needed to be sent information about the session that generated the error, like QueryString & Form variables, Server Variables and Cookies. This kind of information helps tremendously in the bug-tracking process.We wanted to get the variables into a DataTable so that later we could easily bind it to a DataGrid. The variables are either stored in a NameValueCollection or an HttpCookiesCollection, so I wrote a couple of functions that iterate through the collections and add rows to a datatable:
Private Function GetVariables(ByVal inputVarCollection As System.Collections.Specialized.NameValueCollection) As DataTable
Dim objTable As New DataTable()
objTable.Columns.Add("Name", GetType(String))
objTable.Columns.Add("Value", GetType(String))
Dim strItem As String
Dim objRow As DataRow
For Each strItem In inputVarCollection
objRow = objTable.NewRow()
objRow("Name") = strItem
objRow("Value") = inputVarCollection(strItem)
objTable.Rows.Add(objRow)
Next
Return objTable
End Function
Private Function GetCookieVars() As DataTable
Dim objTable As New DataTable()
objTable.Columns.Add("Name", GetType(String))
objTable.Columns.Add("Value", GetType(String))
Dim strItem As String
Dim objRow As DataRow
For Each strItem In HttpContext.Current.Request.Cookies
objRow = objTable.NewRow()
objRow("Name") = strItem
objRow("Value") = HttpContext.Current.Request.Cookies(strItem).Value
objTable.Rows.Add(objRow)
Next
Return objTable
End Function
[bold]Creating the DataGrids[/bold]I fashioned the error e-mail after the output generated when you use ASP.NET tracing. The easiest way to do this was to use DataGrids, but since they were all going to be the same design and they needed to be programmatically generated on the fly, I wrote a method that set up the templates for the grid:
Private Function CreateDataGrid() As System.Web.UI.WebControls.DataGrid
Dim objDataGrid As New DataGrid()
objDataGrid.Width = System.Web.UI.WebControls.Unit.Percentage(100)
objDataGrid.BorderWidth = System.Web.UI.WebControls.Unit.Pixel(0)
objDataGrid.CellPadding = "2"
objDataGrid.HeaderStyle.BackColor = System.Drawing.Color.LightGray
objDataGrid.HeaderStyle.ForeColor = System.Drawing.Color.Black
objDataGrid.HeaderStyle.Font.Name = "Arial"
objDataGrid.HeaderStyle.Font.Size = System.Web.UI.WebControls.FontUnit.Point(10)
objDataGrid.HeaderStyle.Font.Bold = True
objDataGrid.ItemStyle.BackColor = System.Drawing.Color.White
objDataGrid.ItemStyle.ForeColor = System.Drawing.Color.Black
objDataGrid.ItemStyle.Font.Name = "Arial"
objDataGrid.ItemStyle.Font.Size = System.Web.UI.WebControls.FontUnit.Point(10)
objDataGrid.AlternatingItemStyle.BackColor = System.Drawing.ColorTranslator.FromHtml("#eeeeee")
objDataGrid.AlternatingItemStyle.ForeColor = System.Drawing.Color.Black
objDataGrid.AlternatingItemStyle.Font.Name = "Arial"
objDataGrid.AlternatingItemStyle.Font.Size = System.Web.UI.WebControls.FontUnit.Point(10)
Return objDataGrid
End Function
[bold]Creating the e-mail[/bold]This is the most complicated step of the process and one of the main reasons that we went with the aspNetEmail component. System.Web.Mail didn?t allow us to add controls (like DataGrid) to an e-mail message, so we would have had to build a lot of ugly ASP-like code to generate nice, uniform looking tables. Why reinvent the wheel when there are server controls that do the dirty work for you? We were able to add the DataGrid controls to our e-mail messages using aspNetEmail?s AppendControlToBody function. The code below will add a DataGrid containing cookie information and send the e-mail:
Dim objMessage
As New EmailMessage("your smtp server")
Dim objCookiesDG As DataGrid = CreateDataGrid()
objCookiesDG.DataSource = GetCookieVars()
objCookiesDG.DataBind()
objMessage.AppendControlToBody(objCookiesDG)
objMessage.FromAddress = "e-mail address"
objMessage.To = "comma separated e-mail addresses"
objMessage.Subject = "Error: Portal Error"
objMessage.BodyFormat = MailFormat.Html
objMessage.Send()
[bold]Conclusion[/bold]It is super easy to globally handle and trap errors at an application level, and with a couple of steps, you can create e-mail notification of those errors in a standard, easy to read format. You can view the entire ErrorHandlerClass below:
Imports System
.Text
Imports aspNetEmail
Public Class ErrorHandler
Private Function CreateDataGrid() As System.Web.UI.WebControls.DataGrid
Dim objDataGrid As New DataGrid()
objDataGrid.Width = System.Web.UI.WebControls.Unit.Percentage(100)
objDataGrid.BorderWidth = System.Web.UI.WebControls.Unit.Pixel(0)
objDataGrid.CellPadding = "2"
objDataGrid.HeaderStyle.BackColor = System.Drawing.Color.LightGray
objDataGrid.HeaderStyle.ForeColor = System.Drawing.Color.Black
objDataGrid.HeaderStyle.Font.Name = "Arial"
objDataGrid.HeaderStyle.Font.Size = System.Web.UI.WebControls.FontUnit.Point(10)
objDataGrid.HeaderStyle.Font.Bold = True
objDataGrid.ItemStyle.BackColor = System.Drawing.Color.White
objDataGrid.ItemStyle.ForeColor = System.Drawing.Color.Black
objDataGrid.ItemStyle.Font.Name = "Arial"
objDataGrid.ItemStyle.Font.Size = System.Web.UI.WebControls.FontUnit.Point(10)
objDataGrid.AlternatingItemStyle.BackColor = System.Drawing.ColorTranslator.FromHtml("#eeeeee")
objDataGrid.AlternatingItemStyle.ForeColor = System.Drawing.Color.Black
objDataGrid.AlternatingItemStyle.Font.Name = "Arial"
objDataGrid.AlternatingItemStyle.Font.Size = System.Web.UI.WebControls.FontUnit.Point(10)
Return objDataGrid
End Function
Private Function GetVariables(ByVal inputVarCollection As System.Collections.Specialized.NameValueCollection) As DataTable
Dim objTable As New DataTable()
objTable.Columns.Add("Name", GetType(String))
objTable.Columns.Add("Value", GetType(String))
Dim strItem As String
Dim objRow As DataRow
For Each strItem In inputVarCollection
objRow = objTable.NewRow()
objRow("Name") = strItem
objRow("Value") = inputVarCollection(strItem)
objTable.Rows.Add(objRow)
Next
Return objTable
End Function
Private Function GetCookieVars() As DataTable
Dim objTable As New DataTable()
objTable.Columns.Add("Name", GetType(String))
objTable.Columns.Add("Value", GetType(String))
Dim strItem As String
Dim objRow As DataRow
For Each strItem In HttpContext.Current.Request.Cookies
objRow = objTable.NewRow()
objRow("Name") = strItem
objRow("Value") = HttpContext.Current.Request.Cookies(strItem).Value
objTable.Rows.Add(objRow)
Next
Return objTable
End Function
Public Sub SendHtmlErrorEmail(ByVal ex As Exception)
Dim objMessage As New EmailMessage("your smtp server")
objMessage.Body = "<SPAN STYLE=""font-size:18pt; color: red;font-family: Arial;"">Portal Error - " & ex.Message & "</SPAN>
"
Dim objErrInfoDG As DataGrid = CreateDataGrid()
objMessage.Body &= "<TABLE BORDER=0 WIDTH=100% CELLPADDING=1 CELLSPACING=0><TR><TD STYLE=""background-color: black; color: white;font-weight: bold;font-family: Arial;"">Error information</TD></TR></TABLE>"
Dim objTable As New DataTable()
objTable.Columns.Add("Name", GetType(String))
objTable.Columns.Add("Value", GetType(String))
Dim objRow As DataRow
objRow = objTable.NewRow()
objRow("Name") = "Message"
objRow("Value") = ex.Message
objTable.Rows.Add(objRow)
objRow = objTable.NewRow()
objRow("Name") = "Source"
objRow("Value") = ex.Source
objTable.Rows.Add(objRow)
objRow = objTable.NewRow()
objRow("Name") = "TargetSite"
objRow("Value") = ex.TargetSite.ToString()
objTable.Rows.Add(objRow)
objRow = objTable.NewRow()
objRow("Name") = "StackTrace"
objRow("Value") = ex.StackTrace
objTable.Rows.Add(objRow)
objErrInfoDG.DataSource = objTable
objErrInfoDG.DataBind()
objMessage.AppendControlToBody(objErrInfoDG)
objMessage.Body &= "
<TABLE BORDER=0 WIDTH=100% CELLPADDING=1 CELLSPACING=0><TR><TD COLSPAN=2 STYLE=""background-color: black; color: white;font-weight: bold;font-family: Arial;"">Querystring Collection</TD></TR></TABLE>"
Dim objQSDG As DataGrid = CreateDataGrid()
objQSDG.DataSource = GetVariables(HttpContext.Current.Request.QueryString)
objQSDG.DataBind()
objMessage.AppendControlToBody(objQSDG)
objMessage.Body &= "
<TABLE BORDER=0 WIDTH=100% CELLPADDING=1 CELLSPACING=0><TR><TD COLSPAN=2 STYLE=""background-color: black; color: white;font-weight: bold;font-family: Arial;"">Form Collection</TD></TR></TABLE>"
Dim objFormDG As DataGrid = CreateDataGrid()
objFormDG.DataSource = GetVariables(HttpContext.Current.Request.Form)
objFormDG.DataBind()
objMessage.AppendControlToBody(objFormDG)
objMessage.Body &= "
<TABLE BORDER=0 WIDTH=100% CELLPADDING=1 CELLSPACING=0><TR><TD COLSPAN=2 STYLE=""background-color: black; color: white;font-weight: bold;font-family: Arial;"">Cookies Collection</TD></TR></TABLE>"
Dim objCookiesDG As DataGrid = CreateDataGrid()
objCookiesDG.DataSource = GetCookieVars()
objCookiesDG.DataBind()
objMessage.AppendControlToBody(objCookiesDG)
objMessage.Body &= "
<TABLE BORDER=0 WIDTH=100% CELLPADDING=1 CELLSPACING=0><TR><TD COLSPAN=2 STYLE=""background-color: black; color: white;font-weight: bold;font-family: Arial;"">Server Variables</TD></TR></TABLE>"
Dim objServVarDG As DataGrid = CreateDataGrid()
objServVarDG.DataSource = GetVariables(HttpContext.Current.Request.ServerVariables)
objServVarDG.DataBind()
objMessage.AppendControlToBody(objServVarDG)
objMessage.FromAddress = "e-mail address"
objMessage.To = "comma separated e-mail addresses"
objMessage.Subject = "Error: Portal Error"
objMessage.BodyFormat = MailFormat.Html
objMessage.Send()
End Sub
End Class
[bold]About the Author[/bold]Tyler Peelen is the lead ASP.NET developer for the University of Wisconsin ? Stevens Point, my.uwsp.edu portal project. Although he is only 18, he has a firm grasp of ASP.NET has been programming for 10 years. | DISCLAIMER: The content provided in this article is not warranted or guaranteed by Developer Shed, Inc. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. As such it is incumbent upon the reader to employ real-world tactics for security and implementation of best practices. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. If this is a hardware review, it is not recommended to open and/or modify your hardware. |
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