    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.commons.ObjectCreator;
    021import org.apache.tapestry5.ioc.Invokable;
    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}