Last argument of log message stripped if Throwable, even when cause is given as well (original) (raw)

If a Throwable type is passed to match the last {} argument, it is ignored, and the formatted log message will write {} instead.

Example:

package com.test;

import ch.qos.logback.core.Appender; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.slf4j.event.Level;

public class Test { static final Logger log = LoggerFactory.getLogger(Test.class);

public static void main(String[] args) { log.info("SLF4J Version: {}", Logger.class.getPackage().getImplementationVersion()); log.info("Logback Version: {}", Appender.class.getPackage().getImplementationVersion());

Exception ex = new CustomException("Some message");
log.error("Exception Message: {}", ex, ex);

log.makeLoggingEventBuilder(Level.WARN)
    .setMessage("Exception Message: {}")
    .addArgument(ex)
    .setCause(ex)
    .log();

}

static class CustomException extends Exception { public CustomException(String msg) { super(msg); }

@Override
public String toString() {
  return "Custom Message";
}

} }

Expected output:

[main] INFO com.test.Test -- SLF4J Version: 2.0.15
[main] INFO com.test.Test -- Logback Version: 1.5.11
[main] ERROR com.test.Test -- Exception Message: Custom Message
com.test.Test$CustomException: Some message
    at com.test.Test.main(Test.java:15)
[main] WARN com.test.Test -- Exception Message: Custom Message
com.test.Test$CustomException: Some message
    at com.test.Test.main(Test.java:15)

Actual output:

[main] INFO com.test.Test -- SLF4J Version: 2.0.15
[main] INFO com.test.Test -- Logback Version: 1.5.11
[main] ERROR com.test.Test -- Exception Message: {}
com.test.Test$CustomException: Some message
    at com.test.Test.main(Test.java:15)
[main] WARN com.test.Test -- Exception Message: {}
com.test.Test$CustomException: Some message
    at com.test.Test.main(Test.java:15)

Workaround:
Explicitly calling .toString() on the argument (log.error("Exception Message: {}", ex.toString(), ex)), or adding a bogus extra "" argument (log.error("Exception Message: {}", ex, "", ex)) works as a work around, but causes static analysis tools, including the one in IntelliJ, to warn about it.