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DWR is easy Ajax for Java. It makes it simple to call Java code directly from Javascript. It gets rid of almost all the boilerplate code between the web browser and your Java code. This version 4.0.2 works with Jakarta Servlet 4.0.2.

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package org.directwebremoting.datasync;

import java.util.Comparator;
import java.util.List;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.directwebremoting.io.SortCriterion;
import org.directwebremoting.util.LocalUtil;

/**
 * A {@link Comparator} that uses a list of {@link SortCriterion} to decide
 * how to sort the beans. Values to sort by are extracted using an implementation
 * of {@link AttributeValueExtractor},.
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class SortCriteriaComparator implements Comparator
{
    /**
     * All SortCriteriaComparators need a set of things to sort on and a way to
     * get the values to sort
     * @param sort ...
     * @param comparatorFactory ...
     */
    public SortCriteriaComparator(List sort, ComparatorFactory comparatorFactory)
    {
        this.sort = sort;
        this.comparatorFactory = comparatorFactory;
    }

    /* (non-Javadoc)
     * @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
     */
    public int compare(T object1, T object2)
    {
        if (object1 == null)
        {
            if (object2 == null)
            {
                return 0;
            }
            else
            {
                return -1;
            }
        }
        else
        {
            if (object2 == null)
            {
                return 1;
            }
        }

        if (object1.getClass() != object2.getClass())
        {
            log.warn("Classes don't match. Results could be unpredictable: " + object1.getClass() + " / " + object2.getClass());
        }

        try
        {
            for (SortCriterion criterion : sort)
            {
                Comparator comparator = comparatorFactory.getComparator(criterion.getAttribute(), criterion.isAscending());
                int comparison = comparator.compare(object1, object2);
                if (comparison != 0)
                {
                    return comparison;
                }
            }
        }
        catch (Exception ex)
        {
            log.warn("Failure while sorting objects", ex);
        }

        // So we can't tell them apart by comparing them - we can't return 0
        // unless they are equal, so we need to do something determinate
        if (object1.equals(object2))
        {
            return 0;
        }

        int hash1 = object1.hashCode();
        int hash2 = object2.hashCode();
        return LocalUtil.shrink(hash1 - hash2);
    }

    /**
     * The way to extract values to sort on
     */
    private final ComparatorFactory comparatorFactory;

    /**
     * The sort criteria
     */
    private final List sort;

    /**
     * The log stream
     */
    private static final Log log = LogFactory.getLog(SortCriteriaComparator.class);
}