Boolean Expression Evaluation in Java

Question

I\'m looking for a relatively simpler (when compared with writing a parser) way to evaluate boolean expressions in Java, and I do not want to use the JEP library.

I

Answer 1

I found the libraries listed here too complicated for my needs. I ended up using Fscript: http://fscript.sourceforge.net/

Answer 2

You could try this library https://github.com/Shy-Ta/expression-evaluator-demo - the read me has a fair number of examples. The library uses java and groovy.

In addition to supporting this use case, it also supports a lot of other excel like functions. Also, it is very simple to add new functions as demonstrated in the example.

      ExpressionsEvaluator evalExpr = ExpressionsFactory.create("(x > 4 || x < 8 && p > 6)");  
      Map<String, Object> variables = new HashMap<String, Object>();  
      variables.put("x", 100);  
      variables.put("p", 10);
      evalExpr.eval();

Answer 3

try Janino http://docs.codehaus.org/display/JANINO/Home It is very simple to use eg (taken from http://docs.codehaus.org/display/JANINO/Basic):

// Compile the expression once; relatively slow.
ExpressionEvaluator ee = new ExpressionEvaluator(
    "c > d ? c : d",                     // expression
    int.class,                           // expressionType
    new String[] { "c", "d" },           // parameterNames
    new Class[] { int.class, int.class } // parameterTypes
);

// Evaluate it with varying parameter values; very fast.
Integer res = (Integer) ee.evaluate(
    new Object[] {          // parameterValues
        new Integer(10),
        new Integer(11),
    }
);
System.out.println("res = " + res);

Answer 4

Try http://code.google.com/p/xpressionengine/ for open source implementation

Answer 5

Using jexl (http://commons.apache.org/jexl/), you can accomplish this like this

    JexlEngine jexl = new JexlEngine();
    jexl.setSilent(true);
    jexl.setLenient(true);

    Expression expression = jexl.createExpression("(a || b && (c && d))");
    JexlContext jexlContext = new MapContext();

    //b and c and d should pass
    jexlContext.set("b",true);
    jexlContext.set("c",true);
    jexlContext.set("d",true);

    assertTrue((Boolean)expression.evaluate(jexlContext));

    jexlContext = new MapContext();

    //b and c and NOT d should be false
    jexlContext.set("b",true);
    jexlContext.set("c",true);

    //note this works without setting d to false on the context
    //because null evaluates to false

    assertFalse((Boolean)expression.evaluate(jexlContext));

Answer 6

JUEL provides an implementation of Java's Unified Expression Language without being explicitly tied to JSP. Here's its Quick Start guide, expression evaluation (#3 on that page) is the part you're interested in.

Alternatively, Spring 3.0 provides its own (though somewhat similar) expression language. This option only makes sense if you're already using Spring, though - I wouldn't pull it in just for EL.