Using Lambdaj to Navigate Through Dom4j Elements

Question

For anyone familiar with lambdaj (not I) you will have seen this stacktrace, or some variation, before:

ch.lambdaj.function.argument.ArgumentConversionException: Unable to convert the placeholder org.dom4j.tree.AbstractAttribute in a valid argument at ch.lambdaj.function.argument.ArgumentsFactory.actualArgument(ArgumentsFactory.java:92) at ch.lambdaj.function.matcher.HasArgumentWithValue.havingValue(HasArgumentWithValue.java:70) at ch.lambdaj.Lambda.having(Lambda.java:1204)

My understadning is that this happens through a limitation of lambdaj with final classes.

I get the above when testing the following code:

import static ch.lambdaj.Lambda.having;
import static ch.lambdaj.Lambda.selectFirst;
import static org.hamcrest.CoreMatchers.equalTo;

import java.util.List;

import org.dom4j.tree.AbstractAttribute;
public class DocumentUtils {

    public static String getAttributeValueFromListByName(
            List<AbstractAttribute> list, String name) {

        AbstractAttribute requiredAttribute = selectFirst(list,
                having((AbstractAttribute.class).getName(), equalTo(name)));

        String value = requiredAttribute.getValue();

        return value;

    }

}

I had been using dom4j's Attribute interface, getting the same problem, then thought maybe lambdaj doesn't like interfaces.. so I switched to the AbstractAttribute abstract class.

Is there an issue with lambdaj and abstract classes? Or is my method just pants? Any ideas how to solve this?

FYI: I'm using lambdaj 2.4 and dom4j 1.6

Thanks a lot in advance.

Answer 1

Issue 92 has been raised with lambdaj, as requested by Mario Fusco (LambdaJ Developer)

Answer 2

If you're using lambdaj 2.4 you're lucky because this issue has been fixed in that release. The problem and its solution is described in the first point of the release notes of lambdaj 2.4.

In particular lambdaj uses an internal heuristic to create Argument's placeholder, but it doesn't work in some cases, so you can override it as explained there.