001/*
002 * Shredzone Commons
003 *
004 * Copyright (C) 2012 Richard "Shred" Körber
005 *   http://commons.shredzone.org
006 *
007 * This program is free software: you can redistribute it and/or modify
008 * it under the terms of the GNU Library General Public License as
009 * published by the Free Software Foundation, either version 3 of the
010 * License, or (at your option) any later version.
011 *
012 * This program is distributed in the hope that it will be useful,
013 * but WITHOUT ANY WARRANTY; without even the implied warranty of
014 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
015 * GNU General Public License for more details.
016 *
017 * You should have received a copy of the GNU Library General Public License
018 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
019 */
020package org.shredzone.commons.taglib;
021
022import javax.annotation.ParametersAreNonnullByDefault;
023import javax.servlet.jsp.tagext.Tag;
024import javax.servlet.jsp.tagext.TagSupport;
025
026import org.shredzone.commons.taglib.proxy.ProxiedTag;
027
028/**
029 * Utility class for taglib beans.
030 *
031 * @author Richard "Shred" Körber
032 */
033@ParametersAreNonnullByDefault
034public final class TaglibUtils {
035
036    private TaglibUtils() {}
037
038    /**
039     * Finds an ancestor tag of the given type. Starting from the given Tag, it traverses
040     * up the parent tags until a tag of the given type is found.
041     * <p>
042     * Use this method instead of {@link TagSupport#findAncestorWithClass(Tag, Class)}, as
043     * it is aware of proxied tag classes, while findAncestorWithClass only sees the
044     * proxy instances instead of the tag classes behind it. Furthermore, this method is
045     * also able to locate interfaces.
046     *
047     * @param <T>
048     *            Type to find and return
049     * @param from
050     *            Tag to start from
051     * @param type
052     *            Type to find
053     * @return Ancestor of that type, or {@code null} if none was found.
054     */
055    @SuppressWarnings("unchecked")
056    public static <T> T findAncestorWithType(Tag from, Class<T> type) {
057        Tag parent = from.getParent();
058        while (parent != null) {
059            if (parent instanceof ProxiedTag) {
060                parent = ((ProxiedTag<Tag>) parent).getTargetBean();
061            }
062            if (type.isAssignableFrom(parent.getClass())) {
063                return (T) parent;
064            }
065            parent = parent.getParent();
066        }
067        return null;
068    }
069
070}