    001    // Copyright 2009, 2010 The Apache Software Foundation
    002    //
    003    // Licensed under the Apache License, Version 2.0 (the "License");
    004    // you may not use this file except in compliance with the License.
    005    // You may obtain a copy of the License at
    006    //
    007    // http://www.apache.org/licenses/LICENSE-2.0
    008    //
    009    // Unless required by applicable law or agreed to in writing, software
    010    // distributed under the License is distributed on an "AS IS" BASIS,
    011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012    // See the License for the specific language governing permissions and
    013    // limitations under the License.
    014
    015    package org.apache.tapestry5.corelib.internal;
    016
    017    import org.apache.tapestry5.MarkupWriter;
    018    import org.apache.tapestry5.MarkupWriterListener;
    019    import org.apache.tapestry5.dom.Element;
    020    import org.apache.tapestry5.ioc.internal.util.OneShotLock;
    021    import org.apache.tapestry5.services.HiddenFieldLocationRules;
    022
    023    /**
    024     * Used to position a hidden field (as part of a form-related component). Hidden fields are not allowed to go just
    025     * anywhere, there are rules, dictated by the (X)HTML schema, about where they are allowed. We use the
    026     * {@link org.apache.tapestry5.MarkupWriterListener} interface to monitor elements as they are started and ended to find
    027     * a
    028     * place to put content.
    029     */
    030    public class HiddenFieldPositioner
    031    {
    032        /**
    033         * The type of element to create.
    034         */
    035        private static final String ELEMENT = "input";
    036
    037        private final MarkupWriter writer;
    038
    039        private final HiddenFieldLocationRules rules;
    040
    041        private final OneShotLock lock = new OneShotLock();
    042
    043        private Element hiddenFieldElement;
    044
    045        private final MarkupWriterListener listener = new MarkupWriterListener()
    046        {
    047            public void elementDidStart(Element element)
    048            {
    049                if (rules.placeHiddenFieldInside(element))
    050                {
    051                    hiddenFieldElement = element.element(ELEMENT);
    052                    writer.removeListener(this);
    053                }
    054            }
    055
    056            public void elementDidEnd(Element element)
    057            {
    058                if (rules.placeHiddenFieldAfter(element))
    059                {
    060                    hiddenFieldElement = element.getContainer().element(ELEMENT);
    061                    writer.removeListener(this);
    062                }
    063            }
    064        };
    065
    066        public HiddenFieldPositioner(MarkupWriter writer, HiddenFieldLocationRules rules)
    067        {
    068            this.writer = writer;
    069            this.rules = rules;
    070
    071            this.writer.addListener(listener);
    072        }
    073
    074        /**
    075         * Returns the hidden field element, which can have its attributes filled in.
    076         *
    077         * @return the element
    078         * @throws IllegalStateException
    079         *             if the element was not positioned
    080         */
    081        public Element getElement()
    082        {
    083            lock.lock();
    084
    085            // Remove the listener if it hasn't been removed already.
    086
    087            writer.removeListener(listener);
    088
    089            if (hiddenFieldElement == null)
    090                throw new IllegalStateException(
    091                        "The rendered content did not include any elements that allow for the positioning of the hidden form field's element.");
    092
    093            return hiddenFieldElement;
    094        }
    095
    096        /**
    097         * Discard this positioner (an alternative to invoking {@link #getElement()}).
    098         * If an {@link Element} has been created for the hidden field, that
    099         * element is removed.
    100         *
    101         * @since 5.2.0
    102         */
    103        public void discard()
    104        {
    105            lock.lock();
    106
    107            if (hiddenFieldElement != null)
    108                hiddenFieldElement.remove();
    109
    110            writer.removeListener(listener);
    111        }
    112
    113    }