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    }