Many years ago, Liferay's build validation was only getting started and so JSP pre-compilation related slowness wasn't a big deal (I think it was really only used during the distribution process). However, I wanted to make it faster for a client-related project (where we couldn't really do a server warm-up after deployment) and the research culminated in a blog entry summarizing my findings.
Fast forward a few years later and I found out that Liferay QA was suffering from build slowness because Selenium tests have the same requirement of not being able to do a server warm-up before doing tests, and so pre-compilation is turned on. Thus came an improvement to the core build process in LPS-14215 based on the findings of that blog entry.
Fast forward a few more years and JSP pre-compilation is still a standard part of our distribution process. However, after an upgrade to Tomcat 7 for Liferay 6.1, we released milestones for community testing, and the community (as well as other core engineers) reported that everything was very slow the first time you loaded the portal. Poking around, we discovered that Tomcat was recompiling our pre-compiled JSPs when development mode was active.
In a nutshell, we found that any pre-compilation (including the example provided in the Tomcat 7 documentation) will provide zero performance benefit. This is because rather than assuming class files newer than JSP files were up-to-date, Tomcat used the exact file timestamp to determine that, making sure that when Jasper generated the class files, it updated the modified timestamp of the file to be the same as the JSP. This new feature allowed older files to replace newer ones, in case you rolled back a change to a JSP and re-copied it to the application server, but broke JSP pre-compilation.
Thus, we fixed our own tools with LPS-23032. The TimestampUpdater stand-alone program walks the entire directory and makes sure that the class files have the same timestamps as the java files, which (thanks to Jasper itself behaving properly) will have the same timestamps as the jsp files. All this together makes JSP pre-compilation effective again.
Which leads me to the point of this blog entry. Which is, the example script in the previous blog entry has been updated for Tomcat 7 and invokes Liferay's TimestampUpdater to fix file timestamps. This updated example is available in my document library (download here). See the README.txt contained in the example script for additional instructions on how to use it.
Note that this only works for Liferay 6.1 and beyond, because we didn't have to add the class in previous releases (our default bundle was Tomcat 6). If you need to deploy Liferay 6.0 or earlier against Tomcat 7 for whatever reason, you can extract the TimestampUpdater from the portal-impl.jar of Liferay 6.1 and put it in the portal-impl.jar for your version of Liferay.