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.components;
016    
017    import org.apache.hivemind.HiveMind;
018    import org.apache.tapestry.AbstractComponent;
019    import org.apache.tapestry.IMarkupWriter;
020    import org.apache.tapestry.IRequestCycle;
021    
022    /**
023     * A conditional element on a page which will render its wrapped elements zero or one times.
024     * 
025     * @author Howard Lewis Ship, David Solis
026     */
027    
028    public abstract class Conditional extends AbstractComponent
029    {
030        /**
031         * Renders its wrapped components only if the condition is true (technically, if condition
032         * matches invert). Additionally, if element is specified, can emulate that HTML element if
033         * condition is met
034         */
035    
036        protected void renderComponent(IMarkupWriter writer, IRequestCycle cycle)
037        {
038            if (evaluateCondition())
039            {
040                String element = getElement();
041    
042                boolean render = !cycle.isRewinding() && HiveMind.isNonBlank(element);
043    
044                if (render)
045                {
046                    writer.begin(element);
047                    renderInformalParameters(writer, cycle);
048                }
049    
050                renderBody(writer, cycle);
051    
052                if (render)
053                    writer.end(element);
054            }
055        }
056    
057        protected boolean evaluateCondition()
058        {
059            return getCondition() != getInvert();
060        }
061    
062        public abstract boolean getCondition();
063    
064        public abstract boolean getInvert();
065    
066        public abstract String getElement();
067    }