翻译强力驱动I'm looking for an evaluator for simple condition expressions. Expressions should include variables (read only), strings, numbers and some basic operators.
E.g. expressions something like this:
${a} == "Peter" && ( ${b} == null || ${c} > 10 )So far i implemented a rather "magical" parser that returns an AST that i can evaluate, but i can't believe that i'm the first one to solve that problem.
What existing code could i use instead?
What about SPEL (Spring Expression Lang); http://static.springsource.org/spring/docs/3.0.x/reference/expressions.html
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:
Sounds like JEXL might work well for you. Check out its syntax reference.
Why don't you use Rhino? It's a JavaScript engine already present inside the JDK.
It can evaluate whatever you like to write in JS.. take a look here
This simple recursive descent parser evaluates constants as named functions having no parameters.
A very simple and easy to use alternative with a lot of built in excel functions for string, date and number formatting.
The library also allows easy addition of custom functions. A lot of examples available on the git page. A simple example using variables
ExpressionsEvaluator evalExpr = ExpressionsFactory.create("LEFT(City, 3)"); Map variables = new HashMap(); variables.put("City", "New York"); assertEquals("New", evalExpr.eval(variables));