Robert Schaft created LOG4J2-1002:
-------------------------------------
Summary: PatternLayout, newlines and Exceptions
Key: LOG4J2-1002
URL: https://issues.apache.org/jira/browse/LOG4J2-1002
Project: Log4j 2
Issue Type: Bug
Components: Layouts, Pattern Converters
Affects Versions: 2.2
Environment: Windows, eclipse
Reporter: Robert Schaft
I am struggeling to get the PatternLayout right when using %throwable, %ex or
similar.
The first problem is, that if the exception is limited by the number of lines
(e.g. with the option {{short}} or providing a number), the converter
{{ExtendedThrowablePatternConverter}} doesn't attach a newline to the end of
the stack.
On the other hand it does attach a newline at the end of the full stack.
That is why
{quote}
{{<PatternLayout pattern="%msg%n%ex" />}}
{quote}
produces the expected result for message with and without throwables: there are
no empty lines in the log file and every log message starts in a new line.
What about {{%ex\{short\}}}?
{quote}
{{<PatternLayout pattern="%msg%n%ex\{short\}" />}}
{quote}
This has the problem that messages with throwables do not end with a new line.
This produces all kinds of problems.
Ok, let's add a newline
{quote}
{{<PatternLayout alwaysWriteExceptions="false" pattern="%msg%n%ex\{short\}%n"
/>}}
{quote}
This has the problem that messages _without_ throwables are followed by an
empty line. This is not acceptable on the console.
So we need something more complicated:
{quote}
{{<PatternLayout alwaysWriteExceptions="false"
pattern="%msg%replace\{%n%ex\{short\}%n\}\{\[\r\n]+$\}\{\}%n" />}}
{quote}
Yeah! It works (at least on Windows, Unix, Linux, Mac) and if the undocumented
throwable {{separator}} option is not used. But it's ugly and requires the
alwaysWriteExceptions because the throwable pattern detection does not work any
more.
Short Term solution: Always add a newline to the exception.
Long Term Solution:
Add a conversion pattern {{%onThrowable\{pattern1\}\[\{pattern2\}]}} where
pattern1 is appended when there is a throwable attached to the log message and
the optional pattern2 is appended when there is no throwable appended.
The {{alwaysWriteExceptions="false"}} parameter could be replaced by
{{pattern="%onThrowable\{\}"}}
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