CODEWITHSUNDEEP
javaoperator-overloadingjexl
JMax
JMax

Reputation: 1202

Operator overloading/definition for custom classes in Jexl3

I am trying to implement a custom class that should behave like Boolean in Jexl expressions:

Example: Object result = jexl.createExpression("a || b").evaluate(context)

Where aand b are instances of a custom class that contains an boolean and extra information that should be carried through the evaluated expresssion so that it can be accessed in the end in result.

I have read that Jexl3 should support operator overloading and it seems to have all the necessary structures for defining own operators for custom classes - however I am unable to understand what steps are necessary for doing so.

I already tries to extend Uberspect and JexlArithmetic by custom implementations, however I only found out that using toBoolean I can convert my custom objects to Boolean (which makes result a Boolean - hence I loose all the extra information).

How to use/extend Jexl properly to provide boolean operators for custom classes?

Upvotes: 2

Views: 1243

Answers (2)

Pratik
Pratik

Reputation: 988

Just extend JexlArithmetic class and override or method inside.

public class ExtendedJexlArithmetic extends JexlArithmetic
{
    public Object or(YourCustomClass left, YourCustomClass right)
    {
            return left.or(right); // make sure you've implemented 'or' method inside your class
    }
}

And then try below:

JexlContext jexlContext = new MapContext();

jexlContext.set("a", new YourCustomClass());
jexlContext.set("b", new YourCustomClass());

JexlEngine jexlEngine=new JexlBuilder().arithmetic(new ExtendedJexlArithmetic (true)).create();

System.out.println(jexlEngine.createScript("a | b").execute(jexlContext);

Upvotes: 3

henrib
henrib

Reputation: 364

You are on the right path, you need to extend JexlArithmetic and implement your overloads. The various overloadable operators are described in http://commons.apache.org/proper/commons-jexl/apidocs/org/apache/commons/jexl3/JexlOperator.html . There is a test/example in http://svn.apache.org/viewvc/commons/proper/jexl/tags/COMMONS_JEXL_3_1/src/test/java/org/apache/commons/jexl3/ArithmeticTest.java?view=markup#l666 .

Upvotes: 1

Related Questions