Java String and Mathematical Expression Evaluators

问题

We use the Jeks parser at present to evaluate expressions. I cannot see a way to evaluate string expressions with it - for example:

IF( "Test 1" = "Test 2")

Is there anything out there that can evaluate string and mathematical expressions in Java? Preferably free or open source.

Thanks for any help,

Andez

回答1:

There are a lot of tools out there to evaluate expressions; the correct answer will depend on your exact goals.

Two things that I'd look at:

Commons EL, which evaluates JSP 2.0 expression language.
Rhino, which evaluates JavaScript (I think this is part of JDK 1.6, but haven't used it as such).

回答2:

The answer was a posting on the Jeks forum. I got an answer from Manu. I thought it was not active especially as I could not register on it - but that got sorted.

But if anyone has the same problem then the following lines of code will get it working:

ExpressionParser parser; // we did have = new ExpressionParser(new JeksExpressionSyntax(), null);
JeksInterpreter interpreter; //

And to create the interpreter:

interpreter = new JeksInterpreter() {

      @Override
      public Object getBinaryOperatorValue (Object binaryOperatorKey, Object param1, Object param2)
      {
        // Only functions may take a cell set as parameter
        if ( param1 instanceof JeksCellSet || param2 instanceof JeksCellSet)
          throw new IllegalArgumentException ();
        // Enabled comparison between any type supported by Jeks
        else if (binaryOperatorKey.equals (JeksExpressionSyntax.OPERATOR_EQUAL))
          return param1 != null && param1.equals (param2)
                   ? Boolean.TRUE : Boolean.FALSE;
        // Enabled comparison between any type supported by Jeks
        else if (binaryOperatorKey.equals (JeksExpressionSyntax.OPERATOR_DIFFERENT))
          return param1 != null && param1.equals (param2) ? Boolean.FALSE : Boolean.TRUE;
        else
          return super.getBinaryOperatorValue (binaryOperatorKey, param1, param2);
      }
    };

    parser = new ExpressionParser(new JeksExpressionSyntax(), null);

来源：https://stackoverflow.com/questions/3832323/java-string-and-mathematical-expression-evaluators

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