In addition to configuring the logging of the Web server, you can use the logging configuration mechanism provided by ZK. By default, it is disabled. To enable it, you have to specify the following content in WEB-INF/zk.xml. Refer to Appendix B in the Developer's Reference fore more details.

<zk>
    <log>    
    <log-base>org.zkoss</log-base>    
    </log>    
</zk>

Alternatively, you can enable the logging configuration mechanism manually by invoking the init method of LogService as follows.

org.zkoss.util.logging.LogService.init("org.zkoss");

If you want to log not just org.zkoss but everything, you could specify an empty log-base.

Once the mechanism is enabled, ZK looks for i3-log.conf by searching the classpath at startup. If found, ZK loads its content to initialize the log levels. Then, ZK keeps watching this file, and reloads its content if the file is modified.