Java: Library for expression parsing & evaluation with identifiers not known in advance

Question

I need to evaluate a boolean expression. The purpose is to filter a set of tagged items. Tag can be any name (let's say, like Java identifier).

For example:

foo OR (bar AND !baz)

This would be true for items tagged:

foo fee
foo bar boo
bar

I don't know in advance which names will be needed. I've checked JEXL but it has JexlContext, which is basically a Map which needs to be filled prior to evaluation.

I need some library which calls a callback function to decide whether an identifier is true or false. Or any other mechanism to allow identifiers unknown prior to evaluation.

It has to be free as in beer (it's for a Maven plugin), so Jep is out of question.

What can I use?

I found http://docs.codehaus.org/display/JANINO/Home , looking at it — Ondra Žižka, Dec 12 '11 at 18:42

score 1 · Accepted Answer · answered Dec 12 '11 at 18:34

1

You can provide an implementation of JexlContext that does not rely on a Map. Instead of filling it before evaluation, you can treat its checks for has, get as your callbacks, and ignore the calls to set.

answered Dec 12 '11 at 18:34

Sergey Kalinichenko

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Sounds good, I didn't notice it's an interface :) I'll give it a try. – Ondra Žižka Dec 12 '11 at 18:47

score 0 · Answer 2 · answered Dec 12 '11 at 18:33

0

Try Predicate in Google's guava

answered Dec 12 '11 at 18:33

korifey

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Is there some parser for the expression? – Ondra Žižka Dec 12 '11 at 18:35
No it's based on classes and objects. For parsing use ScriptEngine as per response above – korifey Dec 12 '11 at 18:37

score 0 · Answer 3 · answered Dec 12 '11 at 18:35

0

The easiest way is to use JavaScript that is a part of JDK since java 6. Here is an example

    ScriptEngineManager factory = new ScriptEngineManager();
    ScriptEngine engine = factory.getEngineByName("JavaScript");
    // populate variables foo, bar and baz to the engine, e.g.
    engine.put("foo", true);
    engine.put("bar", true);
    engine.put("baz", false);
    engine.eval("foo OR (bar AND !baz)");

For more information take a look on the tutorial from Oracle.

answered Dec 12 '11 at 18:35

AlexR

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How does it handle unknown identifiers? – Ondra Žižka Dec 12 '11 at 18:44
Well actually - I could only set the known to TRUE and if it throws a special exception for that case, I could consider it as false. – Ondra Žižka Dec 12 '11 at 18:44
And one note - JavaScript is not in OpenJDK – Ondra Žižka Dec 12 '11 at 18:45

Java: Library for expression parsing & evaluation with identifiers not known in advance

3 Answers3