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https://issues.apache.org/jira/browse/LOG4J2-1482?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15406562#comment-15406562
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Gary Gregory commented on LOG4J2-1482:
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The problem is in the method
{{org.apache.logging.log4j.core.layout.AbstractStringLayout.serializeToString(Serializer)}}.
This methods "creates" a new event which is then passed to the serializer. The
problem is that by default, the previous log event object is reused and the
{{parameters}} ivar is cleared as part of reusing/reseting the object before it
is handed back to the call site.
In this use case's code path, this only happens when a rollover happens which
then causes the header to be written on in the new file. Writing out the new
header causes a "new" temporary log event to be created.
I have a patch (needs review) that uses the default log factory to create the
log event, which creates a new instance, there is no reuse.
This puts a minor dent in the no-GC epic because we cannot reuse log events
when writing headers and footers.
This should be problem also without the use of slf4j. So I'll add a test case
in core as well.
> Improper header in CsvParameterLayout
> -------------------------------------
>
> Key: LOG4J2-1482
> URL: https://issues.apache.org/jira/browse/LOG4J2-1482
> Project: Log4j 2
> Issue Type: Bug
> Components: Core
> Affects Versions: 2.6.2
> Reporter: Sumit Singhal
> Attachments: csv-with-line-seprator-1.csv,
> csv-with-line-seprator-2.csv, csv-without-line-separator-1.csv,
> csv-without-line-separator-2.csv
>
>
> The header and first record are coming in first line in case of
> CsvParameterLayout. This messes up the header for the first file as well as
> for the subsequent files. And if we use line separator as part of header, the
> first file seems ok but the first record in subsequent files comes out to be
> empty with only commas.
> Copied from the SO post:
> {code:xml}
> <?xml version="1.0" encoding="UTF-8"?>
> <Configuration status="warn" name="MyApp" packages="">
> <Properties>
> <Property name="audit-path">D:/watcher</Property>
> <Property name="file-name">audit</Property>
> <Property name="file-header">param1,param2,param3</Property>
> </Properties>
> <Appenders>
> <RollingFile name="auditfile"
> fileName="${audit-path}/${file-name}.tmp"
> filePattern="${audit-path}/${file-name}-%d{yyyy-MM-dd}-%i.csv">
> <CsvParameterLayout delimiter="," header="${file-header}">
> </CsvParameterLayout>
> <Policies>
> <SizeBasedTriggeringPolicy size="80 B" />
> </Policies>
> <DefaultRolloverStrategy max="2"/>
> </RollingFile>
> </Appenders>
> <Loggers>
> <Root level="info">
> <AppenderRef ref="auditfile" />
> </Root>
> </Loggers>
> {code}
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