What's a good way to parameterize "static" content (e.g. CSS) in a Tomcat webapp?

Question

Some of our CSS files contain parameters that can vary based on the deployment location (dev, QA, prod). For example:

 background: url(#DOJO_PATH#/dijit/themes...)

to avoid hardcoding a path to a particular CDN or locally-hosted Dojo installation.

These values are textually substituted with the real values by a deployment script, when it copies the contents of the webapp into the Tomcat webapps directory. That way the same deployment archive file (WAR + TAR file containing other configuration) can be deployed to dev, QA, and prod, with the varying parameters provided by environment-specific configuration files.

However, I'd like to make the contents of the WAR (including the templatized CSS files) independent of this in-house deployment script. Since we don't really have control over the deployment script, all I can think to do is configure Tomcat with #DOJO_PATH# etc. as environment variables in the application's context.xml, and use Tomcat to insert those parameters into the CSS at runtime.

I could make the CSS files into generated JSPs, but it seems a little ugly to me. Moreover, the substitution only needs to be done once per application deployment, so repeatedly dynamically generating the stylesheets using JSP will be rather wasteful.

Does anyone have any alternative ideas or tools to use for this? We're committed to Tomcat and to substituting these parameters at deployment or at runtime (that is, not at build time).

Answer 1

What you're doing at the minute seems like the best solution to me.

You could easily write these files to be served by a Servlet and dynamically replace the contents of them using some view rendering technology such as Freemarker (or even a custom written templating system to replace the keywords, but there are costs associated with doing so.

Tomcat can serve these resources much more efficiently if they are truly static at runtime. Also if you front your Tomcat server with Apache then you can have Apache serve the static content without ever hitting your Tomcat server, thus keeping your JVM thread pool smaller and less highly contended.

Answer 2

You could also have a single environment variable that pointed at an environment-specific configuration file, and have some startup scripts plug it together for you at that point. That way, the command line doesn't get out of control.