Recently upgrading to java version "1.6.0_24", jps and jstat seemed to be broken to get monitoring information from running tomcat process.
By default java.io.tmpdir is /tmp, however tomcat usually uses it's own temp directory. That is where jps/jstat looks for hsperfdata_* dirs. If java.io.tmpdir is not set, it would look in /tmp. If jps can't find the hsperfdata directory, it won't report anything.
jps/jstat however allows to specify java.io.tmpdir in case you're using a JVM that places those directories in a different location.
So to get it to work:
$JAVA_HOME/bin/jps -J-Djava.io.tmpdir=/path/to/tomcat/temp -l
$JAVA_HOME/bin/jstat -J-Djava.io.tmpdir=/path/to/tomcat/temp -gc $PID