log4j2.xml file has KeyValuePair set in MDC. If key is not set, how can we omit the value altogether from the log line?

Question

If I have a KeyValuePair in my JsonLayout appender, and that pair is not set in the MDC, is there a way to exclude the value from the logs?

Answer 1

I used a routing appender with a js script. The script grabs the variable into a variable and compares it to itself. If the value is equal to its own replacer - it means it wasn't replaced. In this case, I don't route to the appender that has that KeyValuePair - I route to another one that doesn't.

Answer 2

In Java,

You can use ':-' for null value in log4j2.xml

Example:

<KeyValuePair key="traceId" value="$${ctx:traceId:-}"/>