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https://issues.apache.org/jira/browse/LOG4J2-921?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14247773#comment-14247773
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Remko Popma commented on LOG4J2-921:
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The problem seems to be that the custom lookup always returns the same value,
even though it is designed to return a different value on the first call
(system startup) than subsequent calls (rollover).
I looked at the source but it seems to be doing the right thing: at every
rollover, the header is obtained from the layout. PatternLayout.getHeader()
returns StrSubstitutor.replace(headerString)... Is the value (the result of the
lookup) cached anywhere?
> Allow to log some important information at the start of each new roll over
> log file when using RollingFile Appender
> -------------------------------------------------------------------------------------------------------------------
>
> Key: LOG4J2-921
> URL: https://issues.apache.org/jira/browse/LOG4J2-921
> Project: Log4j 2
> Issue Type: Improvement
> Components: Appenders
> Affects Versions: 2.1
> Reporter: Setu
>
> if someone wants to log some important information at the start of each roll
> over log file there is no mechanism present in current version. The header
> attribute in PatternLayout barely does the job because it logs the header at
> the start of each system startup.
> Example: There is a requirement to log some system properties (or any other
> details, environment details, etc) at the each roll over so that it becomes
> easy to determine on which environment the software is running. When tried to
> use header attribute on a software that continuously runs on server it did
> not work as expected instead the header was logged whenever the server got
> restarted.
> Also how can they key supplied in header attribute be logged with line
> breaks.
> Example: when using {{header="$\{java:runtime} - $\{java:vm} - $\{java:os}"}}
> it prints all the information in same line which makes it unreadable if
> someone wants more details.
> Implementing a custom lookup did not help either as all it did was kept
> logging the custom lookup key in header attribute at each system restart
> instead of at the start of new rollover file.
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