Lightweight template engine in Java

Question

I am looking for a lightweight template engine in Java. I want to be to give my users the ability to define a template in the line of:

"Some arbitrary text ${some_function(Some more text ${1}, function_param)} whatever"

And the template will be compiled and filled in runtime. Requirements are:

• Template accepts array of objects as parameters (and extracts them using expressions like ${0} when 0 is the number of parameter)
• Template has functions that modify their contents. For instance: ${trim(^^^bla bla ${0})} with argument ["bla^^^"] will return "bla bla bla" (^ = space. The site strips my extra spaces)
• Functions can accept parameters. For instance ${substring(Whatever, 4, 8)} will return "ever".
• Functions can be nested. A function operates on it's data after the inner function has been evaluated.
• Functions are extensible, I want to be able to define my own.
• My software is embedded in other production systems, so it has to be as small as possible (I don't want a gigantic framework with a tiny template engine that does what I need).
• From that reason, performance is an issue. I can afford slow compilation time, but template-filling time has to be as fast as possible.
• We use javaSE 1.4. Can't go higher, it's one of our features.

I don't think it's a very complicated requirement so I could write something like that myself, BUT since this is really a marginal feature in our product, I am reluctant to spend time on it, plus it seems like such a common use case, I'm thinking someone must have done this before.

I've looked at template-engines like Velocity and StringTemplate and FreeMarker. I think they are designed to produce really large documents with complicated templates, when performance is not an issue. I need something small, simple and fast.

Ideas?

Answer 1

If your program deploys in JEE 6, then the Expression Language in JSP and JSF Facelets can do all this out of the box.

If not, then I believe you can get the Expression Language jars from the latest Glassfish and figure out how to glue them with your own application.

Answer 2

Velocity from Apache is a wonderful templating engine.

Answer 3

I would recommend one of these two:

• MVEL (see the performance comparison), MVEL 1.3.16 supports JDK 1.4
• Embed Groovy (be sure to pre-compile the script), Groovy 1.6 supports JDK 1.4

There are also bunch of other options (Spring EL, JBoss EL, Commons EL, OGNL) but I would consider them to be too heavyweight and slow for your needs (they all depend heavily on reflection).

In any case, you should create your own test and check the performance.

Answer 4

I guess if you didn't like the big guns like Velocity, you could look at Google Closure Templates for Java.

It's pretty simple to use, but the integration with your tools is a bit... manual, for now.

See the "Concepts" section of the documentation I link to to learn what functions are readily available and how you can develop your own.

(sorry, being a new SO user, I can only post one link per answer and cannot link directly to all the things I mention. But you can jump there from that link by looking around the docs).

Answer 5

http://freemarker.org/ is nice and easy to use.

Answer 6

You should look at StringTemplate again.

Answer 7

After profiling my application with the current banal implementation, I figured it's performance is actually good enough and it isn't worth the time incorporating a template engine into it.

Thanks for all your replies, guys.