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.hivemind.impl;
016
017import org.apache.commons.logging.Log;
018import org.apache.hivemind.ApplicationRuntimeException;
019import org.apache.hivemind.InterceptorStack;
020import org.apache.hivemind.internal.Module;
021import org.apache.hivemind.internal.ServiceInterceptorContribution;
022import org.apache.hivemind.internal.ServicePoint;
023import org.apache.hivemind.util.ToStringBuilder;
024
025/**
026 * Implementation of the {@link org.apache.hivemind.InterceptorStack} interface; localizes
027 * error checking in one place.
028 *
029 * @author Howard Lewis Ship
030 */
031public final class InterceptorStackImpl implements InterceptorStack
032{
033    private final Log _log;
034
035    private ServiceInterceptorContribution _contribution;
036    private ServicePoint _sep;
037    private Class _interfaceClass;
038    private Object _top;
039
040    public InterceptorStackImpl(Log log, ServicePoint sep, Object root)
041    {
042        _log = log;
043        _sep = sep;
044        _top = root;
045        _interfaceClass = sep.getServiceInterface();
046    }
047
048    public String toString()
049    {
050        ToStringBuilder builder = new ToStringBuilder(this);
051        builder.append("contribution", _contribution);
052        builder.append("interfaceClass", _interfaceClass);
053        builder.append("top", _top);
054
055        return builder.toString();
056    }
057
058    public String getServiceExtensionPointId()
059    {
060        return _sep.getExtensionPointId();
061    }
062
063    public Module getServiceModule()
064    {
065        return _sep.getModule();
066    }
067
068    public Class getServiceInterface()
069    {
070        return _interfaceClass;
071    }
072
073    public Object peek()
074    {
075        return _top;
076    }
077
078    public void push(Object interceptor)
079    {
080        if (interceptor == null)
081            throw new ApplicationRuntimeException(
082                ImplMessages.nullInterceptor(_contribution, _sep),
083                _contribution.getLocation(),
084                null);
085
086        if (!_interfaceClass.isAssignableFrom(interceptor.getClass()))
087            throw new ApplicationRuntimeException(
088                ImplMessages.interceptorDoesNotImplementInterface(
089                    interceptor,
090                    _contribution,
091                    _sep,
092                    _interfaceClass),
093                _contribution.getLocation(),
094                null);
095
096        _top = interceptor;
097    }
098
099    /**
100     * Invoked to process the next interceptor contribution; these should
101     * be processed in ascending order.
102     * 
103     */
104
105    public void process(ServiceInterceptorContribution contribution)
106    {
107        if (_log.isDebugEnabled())
108            _log.debug("Applying interceptor factory " + contribution.getFactoryServiceId());
109
110        // And now we can finally do this!
111
112        try
113        {
114            _contribution = contribution;
115
116            contribution.createInterceptor(this);
117        }
118        finally
119        {
120            _contribution = null;
121        }
122    }
123
124        public Log getServiceLog()
125        {
126                return _log;
127        }
128}