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
015 package org.apache.tapestry5.ioc.internal;
016
017 import java.util.Collections;
018 import java.util.List;
019
020 import org.apache.tapestry5.ioc.Invokable;
021 import org.apache.tapestry5.ioc.ObjectCreator;
022 import org.apache.tapestry5.ioc.ServiceDecorator;
023 import 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 */
029 public 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 public Object createObject()
053 {
054 Object current = delegate.createObject();
055
056 List<ServiceDecorator> decorators = registry.findDecoratorsForService(serviceDef);
057
058 // We get the decorators ordered according to their dependencies. However, we want to
059 // process from the last interceptor to the first, so we reverse the list.
060
061 Collections.reverse(decorators);
062
063 for (final ServiceDecorator decorator : decorators)
064 {
065 final Object delegate = current;
066
067 Object interceptor = registry.invoke("Invoking " + decorator, new Invokable<Object>()
068 {
069 public Object invoke()
070 {
071 return decorator.createInterceptor(delegate);
072 }
073 });
074
075 // Decorator methods may return null; this indicates that the decorator chose not to
076 // decorate.
077
078 if (interceptor != null)
079 current = interceptor;
080 }
081
082 // The stack of interceptors (plus the core service implementation) are "represented" to the
083 // outside world
084 // as the outermost interceptor. That will still be buried inside the service proxy.
085
086 return current;
087 }
088 }