In Log We Trust (or why did you have to make it so difficult?)

I guess this might be kind of a belated rant… some will know what i’m talking about. At a previous job, we had a need to log stuff: errors, debug info, etc. We were given an API by the upper programmers and it was, shall we say, less than excellent. It was based on some MS application block, which had dependancies on a bunch of other application blocks and made your config files massive. But, boy was it configurable. Blah. The most difficult part was writing out the signature of the method and the parameters. We couldn’t consider doing the values passed in yet. Every time we changed the method signature, we had to alter all the logging statements. We usually ignored logging until late in development when the methods would stabilize.

So I proposed a more simple way. I mean, Reflection is supposed to know all this stuff, right? Why not have it interrogate the current method and pass it and its parameters somewhere to be logged, or at least generated. It was declined. I didn’t take it personally, but inside I was using an evil villain voice: "you fools!"

So when I left, I took my ideas with me and quickly built this into my new application suite. It’s not as wicked-cool as having a config file that can switch between text file and sql logging, in fact, it has NO config file. The simplicity of the logging is the key.

So let’s say you want to log an error. This is all you write:


Catch ex As Exception
    Logging.LogError(ex, System.Reflection.MethodInfo.GetCurrentMethod)

End Try

And it’s the same for every method. That right there is worth its weight in code. But what about when you have parameters? You would need to capture them too. The code is almost unbearable at that point, right?


Catch ex As Exception
    Dim errorParms As New System.Collections.Specialized.StringCollection
    With errorParms
    End With
    Logging.LogError(ex, System.Reflection.MethodInfo.GetCurrentMethod, errorParms)
End Try

So what’s the error log look like? It’s tab-delimited and has the basics of what you need:


4/16/2008 9:04:30 PM 700CB\anachostic WindowsApplication1.Form1.LogWithoutParameters(parm1,parm2) This is a generated error.

4/16/2008 9:04:30 PM 700CB\anachostic WindowsApplication1.Form1.LogWithParameters(parm1=This is parm 1,parm2=12345) This is a generated error.

Have I sold it yet? Or at least given you a starting point for your own logging "framework"? Ahem. Please, it’s just a simple class. Here it is for your plunder:

Imports System.Reflection
Imports System.Collections.Specialized

Public Class Logging

    Public Shared LOGFILE_NAME As String

    Shared Sub New()
        LOGFILE_NAME = "c:\" & My.Application.Info.ProductName & "-Errors.log"

    End Sub

    Shared Sub LogError(ByVal ex As Exception, ByVal method As MethodBase)
        LogError(ex, method, Nothing)
    End Sub

    Shared Sub LogError(ByVal ex As Exception, ByVal method As MethodBase, _
        ByVal parameterValues As StringCollection)

        Dim sb As New System.Text.StringBuilder

            With sb

                If method IsNot Nothing Then
                    .Append(method.ReflectedType.FullName & "." & method.Name)

                    For i As Integer = 0 To method.GetParameters.Length - 1
                        If parameterValues IsNot Nothing _
                            AndAlso i < parameterValues.Count Then
                            .Append("=" & parameterValues(i).Replace(vbCrLf, "<CR>"))
                        End If



                    If sb.ToString.EndsWith(",") Then sb.Length -= 1


                End If


                If ex IsNot Nothing Then
                    .Append(ex.Message.Replace(vbCrLf, "<CR>"))
                End If

            End With

        Catch exc As Exception
            sb.Append("<ERROR WHILE PARSING: " & exc.Message & ">")
        End Try


    End Sub

    Shared Sub LogMessage(ByVal msg As String)
            If Not IO.File.Exists(LOGFILE_NAME) Then
                IO.File.WriteAllText(LOGFILE_NAME, "DATE" _
                    & vbTab & "USER" _
                    & vbTab & "METHOD" _
                    & vbTab & "ERROR MESSAGE" _
                    & vbCrLf)

            End If

            IO.File.AppendAllText(LOGFILE_NAME, msg & vbCrLf)

        Catch ex As Exception

        End Try

    End Sub

End Class