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
015package org.apache.tapestry.annotations;
016
017import java.util.ArrayList;
018import java.util.Collections;
019import java.util.List;
020
021import org.apache.hivemind.ApplicationRuntimeException;
022import org.apache.hivemind.Location;
023import org.apache.tapestry.enhance.EnhancementOperation;
024import 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 */
036public 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}