001    // Copyright 2004, 2005 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.tapestry.html;
016    
017    import org.apache.tapestry.AbstractComponent;
018    import org.apache.tapestry.IAsset;
019    import org.apache.tapestry.IMarkupWriter;
020    import org.apache.tapestry.IRequestCycle;
021    import org.apache.tapestry.Tapestry;
022    
023    /**
024     * Used to insert an image. To create a rollover image, use the {@link Rollover}
025     * class, which integrates a link with the image assets used with the button. [<a
026     * href="../../../../../ComponentReference/Image.html">Component Reference</a>]
027     * 
028     * @author Howard Lewis Ship
029     */
030    
031    public abstract class Image extends AbstractComponent
032    {
033    
034        /**
035         * Renders the &lt;img&gt; element.
036         */
037    
038        protected void renderComponent(IMarkupWriter writer, IRequestCycle cycle)
039        {
040            // Doesn't contain a body so no need to do anything on rewind (assumes
041            // no
042            // sideffects to accessor methods via bindings).
043    
044            if (cycle.isRewinding()) return;
045    
046            IAsset imageAsset = getImage();
047    
048            if (imageAsset == null)
049                throw Tapestry.createRequiredParameterException(this, "image");
050    
051            String imageURL = imageAsset.buildURL();
052    
053            writer.beginEmpty("img");
054    
055            writer.attribute("src", imageURL);
056    
057            renderInformalParameters(writer, cycle);
058    
059            writer.closeTag();
060        }
061    
062        public abstract IAsset getImage();
063    }