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Editorial Team
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Asked: 2026-05-22T00:41:43+00:00

I have a BufferingForwardingAppender configured to forward the last 10 messages to a RollingFileAppender

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I have a BufferingForwardingAppender configured to forward the last 10 messages to a RollingFileAppender when an ERROR occurs. Can I get a custom message to appear in the log before each batch of messages?

I want to indicate that this is a new ERROR event and its context, so that the log is readable?

My log4net configuration is kinda like this:

<appender name="ErrorBufferingAppender" type="log4net.Appender.BufferingForwardingAppender">
  <bufferSize value="10" />
  <lossy value="true" />
  <evaluator type="log4net.Core.LevelEvaluator">
    <threshold value="ERROR" />
  </evaluator>
  <appender-ref ref="ErrorFileAppender" />
</appender>

<appender name="ErrorFileAppender" type="log4net.Appender.RollingFileAppender">
  <param name="File" value="logs\Errors.txt"/>
  <!-- other important parameters -->
  <layout type="log4net.Layout.PatternLayout">
    <conversionPattern value="%date [%-4thread] %-5level %logger{1} - %message%newline"/>
  </layout>
</appender>

And my desired output is kinda like this

---------- ERROR ----------
2011-05-09 16:59:12,327 [8   ] INFO  AppLogger - DiskStorageMonitor.StartMonitoring()
2011-05-09 16:59:12,331 [8   ] INFO  AppLogger - DiskStorageMonitor.Initializing File System Watcher...
2011-05-09 16:59:12,341 [8   ] INFO  AppLogger - DiskStorageMonitor - LocalSlideDataStorageDrive: C:
2011-05-09 16:59:12,370 [8   ] INFO  AppLogger - Transition: From 'MinimumDiskSpaceQuotaState' to 'IdleState'.
2011-05-09 16:59:26,697 [8   ] INFO  AppLogger - Transition: From 'IdleState' to 'SlideHolderMacroState'.
2011-05-09 16:59:26,702 [8   ] INFO  AppLogger - Transition: From 'SlideHolderMacroState' to 'WaitingForMacroCmdResponseState'.
2011-05-09 16:59:26,781 [12  ] INFO  YStageManager - Moving to: -1.25
2011-05-09 16:59:26,782 [14  ] INFO  XStageManager - Moving to: -142
2011-05-09 16:59:30,800 [12  ] ERROR RecoveringErrorHandler - An error occurred. Retrying... (snipped exception message & stacktrace)

---------- ERROR ----------
2011-05-09 16:59:30,808 [12  ] WARN  MacroCameraRecoverySteps - An error occurred while calling the macro camera. Resetting and retrying...
2011-05-09 16:59:30,809 [12  ] INFO  MacroCameraManager - Resetting the Macro Camera.
2011-05-09 16:59:30,886 [12  ] ERROR GetMacroImageCommandHandler - Macro image processing failed for the slide in position 0. (snipped exception message & stacktrace)
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1 Answer

  1. Editorial Team

    I’ve got a solution that will probably work for you but it is a bit of a work-around. Basically, set two appenders to write to the same file. When you write an error (which will trigger the Buffer to clear to your log file), have the other appender write the “——-Error——–” text first with a newline before the text.

    You will have to play around with it a bit to get it to work, but this should be a workable solution. Apache does allow multiple appenders to write to the same file. Just make sure you put the +MinimalLock on your appenders so they don’t lock the file. Here is a SO link that explains how two appenders can write to the same file:

    Can Log4net have multiple appenders write to the same file?

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