Java 中的布尔表达式求值

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 have a String expression like: (x > 4 || x < 8 && p > 6) and my aim is to replace the variables with values.

Is there a way by which I can evaluate this expression?

Bear in mind that this can be any level deep so writing a parser would be very complex.

Answer 1

Use Apache Commons Jexl; which is exactly designed for such requirement.

http://commons.apache.org/jexl/

Answer 2

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 3

You could use the scripting engine in Java6 and the choose any of the popular scripting languages like Scala , Ruby , Python , Groovy , and Javascript . Than all you have to do is make sure the expression you want to evaluate is in the right language. Groovy is probably the easiest and will integrate best.

I have used this method successfully for a feature offering capabilities much like a formula / calculated column in a popular spreadsheet application.

Answer 4

Here is the latest resources for expression evaluation framework

The information page is at http://expressionoasis.vedantatree.com/

Answer 5

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.

Answer 6

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 7

There is a API available at http://lts.online.fr/dev/java/math.evaluator/

Example:

MathEvaluator m = new MathEvaluator("-5-6/(-2) + sqr(15+x)");
m.addVariable("x", 15.1d);
System.out.println( m.getValue() );

Answer 8

尝试http://code.google.com/p/xpressionengine/开源实现

Answer 9

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 10

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