LOG4J2-2749 - fix JSON Layout output containing empty values while configured otherwise

[akhomchenko]

Description

Log4jJsonObjectMapper has JsonInclude.Include.NON_EMPTY enabled but it is not working at the moment - keys with empty values are still present in output. It is caused by bug in jackson-databind which I have fixed. Fix was released as part of jackson-databind:2.11.x.

Why LOG4J2-2749?

I feel this fix will address user request.

Issue itself

log4j2.xml

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <JsonLayout compact="true" properties="true">
                <KeyValuePair key="empty" value="${ctx:empty:-}"/>
            </JsonLayout>
        </Console>
    </Appenders>
    <Loggers>
        <Root level="DEBUG">
            <AppenderRef ref="Console"/>
        </Root>
    </Loggers>
</Configuration>

Main.java

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class Main {
    private static final Logger logger = LogManager.getLogger();

    public static void main(String[] args) {
        logger.info("info");
    }
}

Output

{"instant":{"epochSecond":1590743485,"nanoOfSecond":93000000},"thread":"main","level":"INFO","loggerName":"org.apache.logging.log4j.core.Main","message":"info","endOfBatch":false,"loggerFqcn":"org.apache.logging.log4j.spi.AbstractLogger","contextMap":{},"threadId":1,"threadPriority":5,"empty":""}

Notes

• I have chosen release-2.x while I have actually developed a patch on 2.13.3 tag. I can rebase to any other brach, just let me know which one.

[vy]

Thanks for the patch @gagoman! release-2.x builds are failing right now due to some other problem. Once they got fixed, I will merge the PR.

[akhomchenko]

Awesome, thanks! Please let me know if any changes or rebase to other branch is required.

[akhomchenko]

@vy sorry for a ping. Any chance to get this merged?

[vy]

Hey @gagoman! We already have the Jackson version upgrade along with another change (#335) waiting for its last review by @rgoers. Nevertheless, your changes include a test, which is good. Hence I am merging it.