Michiel Graat created LOG4J2-2945:
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Summary: Better validation and messaging for classpath issues
Key: LOG4J2-2945
URL: https://issues.apache.org/jira/browse/LOG4J2-2945
Project: Log4j 2
Issue Type: Improvement
Components: Boot, Core
Affects Versions: 2.13.3
Reporter: Michiel Graat
Hi,
[~ckozak] suggested I created an issue for this on the [mailing
list|https://lists.apache.org/thread.html/r1de0b24e43b126bc6c05c1b092b18c8bbb3c1418a289c46cb485aa0f%40%3Clog4j-user.logging.apache.org%3E].
While migrating from Log4J 1.x to Log4J2 I accidently left a stray Log4J 1.x
JAR in my application artifact (and thus on the classpath). This lead to some
strange behavior: the logging to the root appender worked, but the other
loggers I defined where ignored (that is, the files were created but they
remained empty).
It was never clear there was a classpath issue, even the Log4J2 trace logging
gave no further information.
So this is a request to improve the validation and messaging on this issue.
Carter suggested the following as a starting point:
{quote}I've written similar validation for slf4j bindings elsewhere that we may
be able to leverage (though the general case has many edge cases that I haven't
thought through yet):
{{/**}}
{{* Validate that there is only one slf4j binding present. If there are
multiple distinct bindings logging will}}
{{* disappear into the void depending on classpath order.}}
{{*/}}
{{private static void validateSlf4jBindings() {}}
{{ try {}}
{{ List<URL> slf4jBindings = Collections.list(}}
{{ getClassLoader().getResources("org/slf4j/impl/StaticLoggerBinder.class"));}}
{{ if (slf4jBindings.size() > 1) {}}
{{ String message = "Detected multiple Slf4j bindings: " + slf4jBindings;}}
{{ // Write to standard streams, if the exception is caught and logged, it may
not be recorded.}}
{{ System.err.println(message);}}
{{ throw new IllegalStateException(message);}}
{{ }}}
{{ } catch (IOException e) {}}
{{ throw new IllegalStateException("Failed to discover slf4j bindings", e);}}
{{ }}}
{{}}}{quote}
Cheers,
Michiel
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