Using the Tomcat Manager

One method of re-starting the SyMBA web application on Tomcat is as follows:

  • Stop Tomcat

  • Delete the old symba.war and associated symba/ directory from Tomcat's webapps/ directory

  • Copy the new symba.war into Tomcat's webapps/ directory

  • Start Tomcat

However, this involves stopping and starting Tomcat each time you make a change. There is an easier way: using your Tomcat Manager. With the manager, you can re-deploy a war file without stopping the Tomcat server.

The first step is to make a user for Tomcat that has permissions to use the Tomcat Manager. Go into the directory containing your Tomcat installation. Find the conf/tomcat-users.xml file and add a user with the "manager" role. Below is an example (complete) tomcat-users.xml file:

  <?xml version='1.0' encoding='utf-8'?>
    <role rolename="manager"/>
    <user username="tomcat" password="tomcat" roles="manager"/>

Ensure that you've restarted Tomcat to have the changes take effect, and then go to the root URL for your Tomcat installtion (e.g. if Tomcat is installed on your local machine on port 8081, then go to http://localhost:8081). You should get a welcome to Tomcat screen, which states "If you're seeing this page via a web browser, it means you've setup Tomcat successfully. Congratulations!". On the left-hand side is a menu. The second item on the menu is "Tomcat Manager". Click on this. The following screen allows you to deploy and undeploy wars to your heart's content, without having to restart Tomcat. However, you need to watch for dragons when using the Tomcat Manager. Details of possible problems with using it are in the next section.

"PermGen Space" Error

As described here , when you undeploy a webapp using Tomcat Manager, the classes aren't neccessarily garbage collected. This means that, over time, when you undeploy/deploy multiple times in a single Tomcat instance using the manager, you will eventually get an OutOfMemory Exception, with a mention of "PermGen Space". This may happen with a properly-controlled exception, or may show itself with a blank jsp that just doesn't seem to load properly. As SyMBA uses CGLIB, commons-logging, spring and hibernate (all culprits mentioned in the web page below), it will be tough going through with a profiler and finding all instances where it's not being garbage collected. Until there are the resources to do this, there is a simple answer: Just stop and restart your Tomcat Server. This sort of error always happens early on, so you can test after a deploy to see if it is happening. You don't need to re-deploy or anything after such an error, just stop and start Tomcat.

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