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
015package org.apache.tapestry.services.impl;
016
017import org.apache.hivemind.ApplicationRuntimeException;
018import org.apache.hivemind.ServiceImplementationFactory;
019import org.apache.hivemind.ServiceImplementationFactoryParameters;
020import org.apache.hivemind.lib.DefaultImplementationBuilder;
021import org.apache.tapestry.spec.IApplicationSpecification;
022
023/**
024 * An implementation of {@link org.apache.hivemind.ServiceImplementationFactory}that looks for a
025 * service implementation provided as an
026 * {@link org.apache.tapestry.spec.ILibrarySpecification#getExtension(String) application
027 * extension}. If no such extension exists, then a
028 * {@link org.apache.hivemind.lib.DefaultImplementationBuilder default implementation}is
029 * constructed and returned instead. This allows compatibility with Tapestry 3.0 and earlier
030 * application extensions (though those will be phased out in the future).
031 * 
032 * @author Howard Lewis Ship
033 * @since 4.0
034 */
035public class ExtensionLookupFactory implements ServiceImplementationFactory
036{
037    private IApplicationSpecification _specification;
038
039    private DefaultImplementationBuilder _defaultBuilder;
040
041    public Object createCoreServiceImplementation(
042            ServiceImplementationFactoryParameters factorParameters)
043    {
044        ExtensionLookupParameter p = (ExtensionLookupParameter) factorParameters.getParameters()
045                .get(0);
046
047        String extensionName = p.getExtensionName();
048
049        Class serviceInterface = factorParameters.getServiceInterface();
050
051        try
052        {
053            if (_specification.checkExtension(extensionName))
054                return _specification.getExtension(extensionName, serviceInterface);
055
056            if (p.getDefault() != null)
057                return p.getDefault();
058
059            return _defaultBuilder.buildDefaultImplementation(serviceInterface);
060        }
061        catch (Exception ex)
062        {
063            throw new ApplicationRuntimeException(ex.getMessage(), p.getLocation(), ex);
064        }
065    }
066
067    public void setDefaultBuilder(DefaultImplementationBuilder builder)
068    {
069        _defaultBuilder = builder;
070    }
071
072    public void setSpecification(IApplicationSpecification specification)
073    {
074        _specification = specification;
075    }
076
077}