Open Source Expression Engines (Java)

Question

Are there any good open source expression engines for java? I am not looking for a rules engine (which implement conditionals and logic).

I want to be able to define a number of "facts" and dynamically generate expressions based on these facts.

For example:

Say I have facts such as:

Lemons=$5
IceCubes=$1
Cups=$2
Water=$1.50

I want to be able to dynamically define an expression:

COSTPERPITCHER=3 * LEMONS + ICECUBES + WATER
and
COSTPERCUP = COSTPERPITCHER / 25 + CUPS

I'd like to be able to store these expressions in a database or created dynamically.

Answer 1

If you just need expression evaluation, take a look at JUEL. Spring 3.0 has Spring expression language - might be worth looking at that too.

If you need actual variables, perhaps Rhino would help.

Answer 2

How about Apache Commons EL?

It was originally geared towards JSP expressions, but now it can be used as a standalone expression evaluator. I've never used it, but it's worth a look.

Answer 3

http://mvel.codehaus.org/ - works pretty good

Answer 4

Lately, I have been using Groovy to serve as an all purpose expression language. The advantage to groovy is that you don't need to learn a brand new syntax. You essentially write code to evaluate, bind in the variables required as a context and execute your script.

Groovy's String capabilities make this very easy to do.

For more information on using groovy inside Java as a scripting language, you can see this page: http://groovy.codehaus.org/Scripts+and+Classes