Spawning a tomcat server instance from within Netbeans is really handy for rapid Java Servlet or JavaServer Pages application development. Since log levels are usually quite verbose during development, logs tend to pile up. So you might want to clean out the log directory from time to time. Or maybe you just want to go through one of those logs one more time with a proper editor.
Here’s Nebeans’ default tomcat log file storage location:

~/.netbeans/<netbeans-version>/apache-tomcat-<tomcat-version>_base/logs

So for a current Netbeans with a recent tomcat version this could be something like ~/.netbeans/8.1/apache-tomcat-8.0.27.0_base/logs/