001// Copyright 2006, 2007, 2008, 2009, 2011 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.tapestry5.ioc.internal;
016
017import java.util.Collections;
018import java.util.List;
019
020import org.apache.tapestry5.ioc.Invokable;
021import org.apache.tapestry5.ioc.ObjectCreator;
022import org.apache.tapestry5.ioc.ServiceDecorator;
023import org.apache.tapestry5.ioc.def.ServiceDef3;
024
025/**
026 * Responsible for constructing the interceptor stack, on demand, by invoking an ordered series of decorators (
027 * {@link org.apache.tapestry5.ioc.def.DecoratorDef} (which are converted into {@link ServiceDecorator}s).
028 */
029public class InterceptorStackBuilder implements ObjectCreator
030{
031    private final ServiceDef3 serviceDef;
032
033    private final ObjectCreator delegate;
034
035    private final InternalRegistry registry;
036
037    /**
038     * @param serviceDef
039     *            service begin decorated
040     * @param delegate
041     *            responsible for creating the object to be decorated
042     * @param registry
043     *            access to service decorators
044     */
045    public InterceptorStackBuilder(ServiceDef3 serviceDef, ObjectCreator delegate, InternalRegistry registry)
046    {
047        this.serviceDef = serviceDef;
048        this.delegate = delegate;
049        this.registry = registry;
050    }
051
052    @Override
053    public Object createObject()
054    {
055        Object current = delegate.createObject();
056
057        List<ServiceDecorator> decorators = registry.findDecoratorsForService(serviceDef);
058
059        // We get the decorators ordered according to their dependencies. However, we want to
060        // process from the last interceptor to the first, so we reverse the list.
061
062        Collections.reverse(decorators);
063
064        for (final ServiceDecorator decorator : decorators)
065        {
066            final Object delegate = current;
067
068            Object interceptor = registry.invoke("Invoking " + decorator, new Invokable<Object>()
069            {
070                @Override
071                public Object invoke()
072                {
073                    return decorator.createInterceptor(delegate);
074                }
075            });
076
077            // Decorator methods may return null; this indicates that the decorator chose not to
078            // decorate.
079
080            if (interceptor != null)
081                current = interceptor;
082        }
083
084        // The stack of interceptors (plus the core service implementation) are "represented" to the
085        // outside world
086        // as the outermost interceptor. That will still be buried inside the service proxy.
087
088        return current;
089    }
090}