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https://issues.apache.org/jira/browse/LOG4J2-2945?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Carter Kozak reassigned LOG4J2-2945:
------------------------------------
Assignee: Carter Kozak
> 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
> Assignee: Carter Kozak
> Priority: Minor
>
> 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):
> {code}/**
> * 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);
> }
> }
> {code}
> {quote}
> Cheers,
> Michiel
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