org.zkoss.util.logging.realCauseBriefly
From Documentation
org.zkoss.util.logging.realCauseBriefly
Default: 6 [Since 3.6.1]
It defines the number of lines to log an error message.
If nonpositive is specified, the full stack traces are logged. Notice that # of lines don't include packages starting with java, javax, sun, or bsh.