001    package org.apache.tapestry.annotations;
002    
003    import java.util.ArrayList;
004    import java.util.Collections;
005    import java.util.List;
006    
007    import org.apache.hivemind.ApplicationRuntimeException;
008    import org.apache.hivemind.Location;
009    import org.apache.tapestry.enhance.EnhancementOperation;
010    import org.apache.tapestry.spec.IComponentSpecification;
011    
012    /**
013     * Recognizes the {@link org.apache.tapestry.annotations.Meta} annotation, and converts it into
014     * properties on the specification. It is desirable to have meta data in base classes be "merged"
015     * with meta data from sub classes, with the sub classes overriding any conflicting elements from
016     * the base class. What we do is work our way up the inheritance tree to java.lang.Object and work
017     * with each Meta annotation we find.
018     * 
019     * @author Howard M. Lewis Ship
020     * @since 4.0
021     */
022    public class MetaAnnotationWorker implements ClassAnnotationEnhancementWorker
023    {
024    
025        public void performEnhancement(EnhancementOperation op, IComponentSpecification spec,
026                Class baseClass, Location location)
027        {
028            List<Meta> metas = assembleMetas(baseClass);
029    
030            for (Meta meta : metas)
031                applyPropertiesFromMeta(meta, spec, location);
032        }
033    
034        private List<Meta> assembleMetas(Class baseClass)
035        {
036            Class searchClass = baseClass;
037            List<Meta> result = new ArrayList<Meta>();
038            Meta lastMeta = null;
039    
040            while (true)
041            {
042                Meta meta = (Meta) searchClass.getAnnotation(Meta.class);
043    
044                // When reach a class that doesn't define or inherit a @Meta, we're done
045                if (meta == null)
046                    break;
047    
048                // Cheap approach, based on annotation inheritance, for determining
049                // whether a meta is already in the result list
050    
051                if (meta != lastMeta)
052                    result.add(meta);
053    
054                searchClass = searchClass.getSuperclass();
055            }
056    
057            Collections.reverse(result);
058    
059            return result;
060        }
061    
062        private void applyPropertiesFromMeta(Meta meta, IComponentSpecification spec, Location location)
063        {
064            String[] pairs = meta.value();
065    
066            for (String pair : pairs)
067            {
068                int equalx = pair.indexOf('=');
069    
070                // The only big problem is that the location will be the location of the @Meta in
071                // the subclass, even if the @Meta with a problem is from a base class.
072    
073                if (equalx < 0)
074                    throw new ApplicationRuntimeException(AnnotationMessages.missingEqualsInMeta(pair),
075                            location, null);
076    
077                String key = pair.substring(0, equalx);
078                String value = pair.substring(equalx + 1);
079    
080                spec.setProperty(key, value);
081            }
082        }
083    }