BeanSorter.java

/*
 * RHQ Management Platform
 * Copyright (C) 2005-2008 Red Hat, Inc.
 * All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation version 2 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
package org.rhq.enterprise.gui.legacy.taglib.display;

import java.lang.reflect.InvocationTargetException;
import java.util.Comparator;
import org.apache.commons.beanutils.PropertyUtils;

/**
 * This utility class is used to sort the list that the table is viewing based on arbitrary properties of objects
 * contained in that list. The only assumption made is that the object returned by the property is either a native type,
 * or implements the Comparable interface. If the property does not implement Comparable, then this little sorter object
 * will just assume that all objects are the same, and quietly do nothing (so you should check for Comparable
 * objecttypes elsewhere as this object won't complain).
 */

class BeanSorter extends Object implements Comparator {
    private String property;
    private Decorator dec;

    /**
     * BeanSorter is a decorator of sorts, you need to initialize it with the property name of the object that is to be
     * sorted (getXXX method name). This property should return a Comparable object.
     */

    protected BeanSorter(String property, Decorator dec) {
        this.property = property;
        this.dec = dec;
    }

    /**
     * Compares two objects by first fetching a property from each object and then comparing that value. If there are
     * any errors produced while trying to compare these objects then a RunTimeException will be thrown as any error
     * found here will most likely be a programming error that needs to be quickly addressed (like trying to compare
     * objects that are not comparable, or trying to read a property from a bean that is invalid, etc...)
     *
     * @throws RuntimeException if there are any problems making a comparison of the object properties.
     */

    public int compare(Object o1, Object o2) throws RuntimeException {
        if (property == null) {
            throw new NullPointerException("Null property provided which " + "prevents BeanSorter sort");
        }

        try {
            Object p1 = null;
            Object p2 = null;

            // If they have supplied a decorator, then make sure and use it for
            // the sorting as well... TODO - Major hack....

            if (this.dec != null) {
                try {
                    dec.initRow(o1, -1, -1);
                    p1 = PropertyUtils.getProperty(dec, property);

                    dec.initRow(o2, -1, -1);
                    p2 = PropertyUtils.getProperty(dec, property);
                } catch (Exception e) {
                    // If there were any problems, then assume that the decorator
                    // does not implement that method, and instead fall down to
                    // the original object...

                    p1 = PropertyUtils.getProperty(o1, property);
                    p2 = PropertyUtils.getProperty(o2, property);
                }
            } else {
                p1 = PropertyUtils.getProperty(o1, property);
                p2 = PropertyUtils.getProperty(o2, property);
            }

            if ((p1 instanceof Comparable) && (p2 instanceof Comparable)) {
                Comparable c1 = (Comparable) p1;
                Comparable c2 = (Comparable) p2;
                return c1.compareTo(c2);
            } else {
                throw new RuntimeException("Object returned by property \"" + property
                    + "\" is not a Comparable object");
            }
        } catch (IllegalAccessException e) {
            throw new RuntimeException("IllegalAccessException thrown while " + "trying to fetch property \""
                + property + "\" during sort");
        } catch (InvocationTargetException e) {
            throw new RuntimeException("InvocationTargetException thrown while " + "trying to fetch property \""
                + property + "\" during sort");
        } catch (NoSuchMethodException e) {
            throw new RuntimeException("NoSuchMethodException thrown while " + "trying to fetch property \"" + property
                + "\" during sort");
        }
    }

    /**
     * Is this Comparator the same as another one...
     */

    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }

        if (obj instanceof BeanSorter) {
            if (this.property != null) {
                return this.property.equals(((BeanSorter) obj).property);
            } else {
                return false;
            }
        } else {
            return false;
        }
    }
}