Question

Is there any Java open-source comparator for comparing beans by multiple fields for multi-column sorting? Each column can be sorted asceding or descending.

For single-column sorting it can be achieved by using org.apache.commons.beanutils.BeanComparator together with org.springframework.util.comparator.InvertibleComparator.

I’m aware that this functionality is quite trivial to write, but what’s the benefit from reinventing the wheel, if it was already written and tested?

Answer 1

I wrote this a few months ago.

public abstract class ChainedComparator<T> implements Comparator<T> {

    private Comparator<T> next;

    @Override
    public int compare(T o1, T o2) {
        int result = doCompare(o1, o2);
        if (result == 0) {
            if (getNext() != null) {
                return getNext().compare(o1, o2);
            }
        }

        return result;
    }

    public abstract int doCompare(T o1, T o2);

    public Comparator<T> getNext() {
        return next;
    }

    public void setNext(Comparator<T> next) {
        this.next = next;
    }
}

Just inherit from this class and override the doCompare-Method. Then set a the next comparator in chain with setNext(). The earlier a comparator appears in this chain, the more “important” it is.

EDIT:

Also see what I found: http://commons.apache.org/collections/api-2.1.1/org/apache/commons/collections/comparators/ComparatorChain.html

This is part of the apache commons collection library, which you can download here