Nice Ant Targets for Updating/Bouncing Tomcat
I've been working with 29West over the last few days and while I can see it's value, it's a little different than server-based messaging systems, and I can see why it's got advantages, and disadvantages. No need to critique it here... it's just what I have to use. But there's a consequence of using 29West's Java API on Tomcat and that's the fact that 29West's Java API uses JNI to get to the real C libraries under the covers.
With JNI, the shared libraries are loaded once in the Tomcat server, but if you want to change the code and remove and install the app again, you're in trouble because the shared library is not unloaded when the class loader is dropped. There's a lot of unhappy people about it, but in the end, there's nothing you can do. You have to remove the web app, shut down the Tomcat instance to drop the shared library, then start up Tomcat again, and then install the web app again.
I wanted it to be easier.
I got an interesting set of targets to do that. First, I need to have the start and stop targets, and they are simply exec targets to the locations of the startup and shutdown scripts:
<target name="start" description="Start Tomcat application"> <exec executable="${catalina.home}/bin/startup.sh"/> </target>
and:
<target name="stop" description="Stop Tomcat application"> <exec executable="${catalina.home}/bin/shutdown.sh"> <arg value="-force"/> </exec> </target>
The value of the argument to shutdown.sh is that if I define:
CATALINA_PID="/usr/local/tomcat/bin/.catalina.pid"
then catalina.sh will save the pid in the file and then on shutdown.sh it'll do a nice kill -9 on that pid and make sure it dies. This is really important because I need to kill the Tomcat instance and I need it to die right now.
Given that we have the standard remove and install targets from the default Tomcat Ant build.xml file, then all I need to do is glue these together:
<target name="update" description="Update the application and bounce the server"> <antcall target="remove"/> <antcall target="stop"/> <antcall target="start"/> <waitfor maxwait="3" maxwaitunit="minute" checkevery="500"> <http url="http://localhost:8080/index.html"/> </waitfor> <antcall target="install"/> </target>
What's happening here is that we're removing the web app from the Tomcat instance, and then shutting him down forcefully. Then we're starting him back up, but since the startup.sh is asynchronous I need to wait until I can get a page back. When I can, then I'll install the web app again.
All in all, it's pretty sweet. It's not as nice a knowing that it's smart enough to unload the shared library, but there's nothing I can do about it. Actually... now that I think about it, I think it'd be better if the loader was smart enough to see that it's the same bloody file and link into it without an issue. But I'm clearly not as clever as these guys.
What I've got is workable, and given the limitations I have (29West and Tomcat), it's as good as I can expect to do for now.