001    // Copyright 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.annotations;
016    
017    import java.util.ArrayList;
018    import java.util.Collections;
019    import java.util.List;
020    
021    import org.apache.hivemind.ApplicationRuntimeException;
022    import org.apache.hivemind.Location;
023    import org.apache.tapestry.enhance.EnhancementOperation;
024    import org.apache.tapestry.spec.IComponentSpecification;
025    
026    /**
027     * Recognizes the {@link org.apache.tapestry.annotations.Meta} annotation, and converts it into
028     * properties on the specification. It is desirable to have meta data in base classes be "merged"
029     * with meta data from sub classes, with the sub classes overriding any conflicting elements from
030     * the base class. What we do is work our way up the inheritance tree to java.lang.Object and work
031     * with each Meta annotation we find.
032     * 
033     * @author Howard M. Lewis Ship
034     * @since 4.0
035     */
036    public class MetaAnnotationWorker implements ClassAnnotationEnhancementWorker
037    {
038    
039        public void performEnhancement(EnhancementOperation op, IComponentSpecification spec,
040                Class baseClass, Location location)
041        {
042            List<Meta> metas = assembleMetas(baseClass);
043    
044            for (Meta meta : metas)
045                applyPropertiesFromMeta(meta, spec, location);
046        }
047    
048        private List<Meta> assembleMetas(Class baseClass)
049        {
050            Class searchClass = baseClass;
051            List<Meta> result = new ArrayList<Meta>();
052            Meta lastMeta = null;
053    
054            while (true)
055            {
056                Meta meta = (Meta) searchClass.getAnnotation(Meta.class);
057    
058                // When reach a class that doesn't define or inherit a @Meta, we're done
059                if (meta == null)
060                    break;
061    
062                // Cheap approach, based on annotation inheritance, for determining
063                // whether a meta is already in the result list
064    
065                if (meta != lastMeta)
066                    result.add(meta);
067    
068                searchClass = searchClass.getSuperclass();
069            }
070    
071            Collections.reverse(result);
072    
073            return result;
074        }
075    
076        private void applyPropertiesFromMeta(Meta meta, IComponentSpecification spec, Location location)
077        {
078            String[] pairs = meta.value();
079    
080            for (String pair : pairs)
081            {
082                int equalx = pair.indexOf('=');
083    
084                // The only big problem is that the location will be the location of the @Meta in
085                // the subclass, even if the @Meta with a problem is from a base class.
086    
087                if (equalx < 0)
088                    throw new ApplicationRuntimeException(AnnotationMessages.missingEqualsInMeta(pair),
089                            location, null);
090    
091                String key = pair.substring(0, equalx);
092                String value = pair.substring(equalx + 1);
093    
094                spec.setProperty(key, value);
095            }
096        }
097    }