Looking for an expression evaluator

Question

I\'m looking for an evaluator for simple condition expressions. Expressions should include variables (read only), strings, numbers and some basic operators.

E.g. exp

Answer 1

Have you looked at MVEL? They provide a getting started guide and performance analysis.

Here's one of their simple examples:

// The compiled expression is serializable and can be cached for re-use.
CompiledExpression compiled = MVEL.compileExpression("x * y"); 

Map vars = new HashMap();
vars.put("x", new Integer(5));
vars.put("y", new Integer(10));

// Executes the compiled expression
Integer result = (Integer) MVEL.executeExpression(compiled, vars); 
assert result.intValue() == 50; 

Also (answering my own question) MVEL seems to provide some support for bytecode generation.

Other alternatives, culling from the above answers and my own:

• Java Expression Parser (JEP) -- and note there is an old version available for free
• Apache Commons JEXL
• With regard to Rhino, here's a dude who did some arithmetic evaluation in that context (looks messy)