001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.commons.configuration2.tree; 018 019import java.util.Collection; 020import java.util.List; 021import java.util.concurrent.atomic.AtomicBoolean; 022 023/** 024 * <p> 025 * A specialized {@code NodeModel} implementation that uses a tracked node 026 * managed by an {@link InMemoryNodeModel} object as root node. 027 * </p> 028 * <p> 029 * Models of this type are useful when working on specific sub trees of a nodes 030 * structure. This is the case for instance for a {@code SubnodeConfiguration}. 031 * </p> 032 * <p> 033 * An instance of this class is constructed with an 034 * {@link InMemoryNodeModelSupport} object providing a reference to the 035 * underlying {@code InMemoryNodeModel} and the {@link NodeSelector} pointing to 036 * the tracked node acting as this model's root node. The {@code NodeModel} 037 * operations are implemented by delegating to the wrapped 038 * {@code InMemoryNodeModel} object specifying the selector to the tracked node 039 * as target root node for the update transaction. Note that the tracked node 040 * can become detached at any time. This situation is handled transparently by 041 * the implementation of {@code InMemoryNodeModel}. The reason for using an 042 * {@code InMemoryNodeModelSupport} object rather than an 043 * {@code InMemoryNodeModel} directly is that this additional layer of 044 * indirection can be used for performing special initializations on the model 045 * before it is returned to the {@code TrackedNodeModel} object. This is needed 046 * by some dynamic configuration implementations, e.g. by 047 * {@code CombinedConfiguration}. 048 * </p> 049 * <p> 050 * If the tracked node acting as root node is exclusively used by this model, it 051 * should be released when this model is no longer needed. This can be done 052 * manually by calling the {@link #close()} method. It is also possible to pass 053 * a value of <strong>true</strong> to the {@code untrackOnFinalize} argument of 054 * the constructor. This causes {@code close()} to be called automatically if 055 * this object gets claimed by the garbage collector. 056 * </p> 057 * <p> 058 * As {@code InMemoryNodeModel}, this class is thread-safe. 059 * </p> 060 * 061 * @since 2.0 062 */ 063public class TrackedNodeModel implements NodeModel<ImmutableNode> 064{ 065 /** Stores the underlying parent model. */ 066 private final InMemoryNodeModelSupport parentModelSupport; 067 068 /** The selector for the managed tracked node. */ 069 private final NodeSelector selector; 070 071 /** 072 * A flag whether the tracked not should be released when this object is 073 * finalized. 074 */ 075 private final boolean releaseTrackedNodeOnFinalize; 076 077 /** A flag whether this model has already been closed. */ 078 private final AtomicBoolean closed; 079 080 /** 081 * Creates a new instance of {@code TrackedNodeModel} and initializes it 082 * with the given underlying model and the selector to the root node. The 083 * boolean argument controls whether the associated tracked node should be 084 * released when this object gets finalized. This allows the underlying 085 * model to free some resources. If used as model within a 086 * {@code SubnodeConfiguration}, there is typically no way to discard the 087 * model explicitly. Therefore, it makes sense to do this automatically on 088 * finalization. 089 * 090 * @param modelSupport the underlying {@code InMemoryNodeModelSupport} (must not be 091 * <b>null</b>) 092 * @param sel the selector to the root node of this model (must not be 093 * <b>null</b>) 094 * @param untrackOnFinalize a flag whether the tracked node should be 095 * released on finalization 096 * @throws IllegalArgumentException if a required parameter is missing 097 */ 098 public TrackedNodeModel(final InMemoryNodeModelSupport modelSupport, final NodeSelector sel, 099 final boolean untrackOnFinalize) 100 { 101 if (modelSupport == null) 102 { 103 throw new IllegalArgumentException( 104 "Underlying model support must not be null!"); 105 } 106 if (sel == null) 107 { 108 throw new IllegalArgumentException("Selector must not be null!"); 109 } 110 111 parentModelSupport = modelSupport; 112 selector = sel; 113 releaseTrackedNodeOnFinalize = untrackOnFinalize; 114 closed = new AtomicBoolean(); 115 } 116 117 /** 118 * Returns the {@code InMemoryNodeModelSupport} object which is used to gain 119 * access to the underlying node model. 120 * 121 * @return the associated {@code InMemoryNodeModelSupport} object 122 */ 123 public InMemoryNodeModelSupport getParentModelSupport() 124 { 125 return parentModelSupport; 126 } 127 128 /** 129 * Returns the parent model. Operations on this model are delegated to this 130 * parent model specifying the selector to the tracked node. 131 * 132 * @return the parent model 133 */ 134 public InMemoryNodeModel getParentModel() 135 { 136 return getParentModelSupport().getNodeModel(); 137 } 138 139 /** 140 * Returns the {@code NodeSelector} pointing to the tracked node managed by 141 * this model. 142 * 143 * @return the tracked node selector 144 */ 145 public NodeSelector getSelector() 146 { 147 return selector; 148 } 149 150 /** 151 * Returns the flag whether the managed tracked node is to be released when 152 * this object gets finalized. This method returns the value of the 153 * corresponding flag passed to the constructor. If result is true, the 154 * underlying model is asked to untrack the managed node when this object is 155 * claimed by the GC. 156 * 157 * @return a flag whether the managed tracked node should be released when 158 * this object dies 159 * @see InMemoryNodeModel#untrackNode(NodeSelector) 160 */ 161 public boolean isReleaseTrackedNodeOnFinalize() 162 { 163 return releaseTrackedNodeOnFinalize; 164 } 165 166 @Override 167 public void setRootNode(final ImmutableNode newRoot) 168 { 169 getParentModel().replaceTrackedNode(getSelector(), newRoot); 170 } 171 172 @Override 173 public NodeHandler<ImmutableNode> getNodeHandler() 174 { 175 return getParentModel().getTrackedNodeHandler(getSelector()); 176 } 177 178 @Override 179 public void addProperty(final String key, final Iterable<?> values, 180 final NodeKeyResolver<ImmutableNode> resolver) 181 { 182 getParentModel().addProperty(key, getSelector(), values, resolver); 183 } 184 185 @Override 186 public void addNodes(final String key, final Collection<? extends ImmutableNode> nodes, 187 final NodeKeyResolver<ImmutableNode> resolver) 188 { 189 getParentModel().addNodes(key, getSelector(), nodes, resolver); 190 } 191 192 @Override 193 public void setProperty(final String key, final Object value, 194 final NodeKeyResolver<ImmutableNode> resolver) 195 { 196 getParentModel().setProperty(key, getSelector(), value, resolver); 197 } 198 199 @Override 200 public List<QueryResult<ImmutableNode>> clearTree(final String key, 201 final NodeKeyResolver<ImmutableNode> resolver) 202 { 203 return getParentModel().clearTree(key, getSelector(), resolver); 204 } 205 206 @Override 207 public void clearProperty(final String key, 208 final NodeKeyResolver<ImmutableNode> resolver) 209 { 210 getParentModel().clearProperty(key, getSelector(), resolver); 211 } 212 213 /** 214 * {@inheritDoc} This implementation clears the sub tree spanned by the 215 * associate tracked node. This has the side effect that this in any case 216 * becomes detached. 217 * 218 * @param resolver the {@code NodeKeyResolver}. 219 */ 220 @Override 221 public void clear(final NodeKeyResolver<ImmutableNode> resolver) 222 { 223 getParentModel().clearTree(null, getSelector(), resolver); 224 } 225 226 /** 227 * {@inheritDoc} This implementation returns the tracked node instance 228 * acting as root node of this model. 229 */ 230 @Override 231 public ImmutableNode getInMemoryRepresentation() 232 { 233 return getNodeHandler().getRootNode(); 234 } 235 236 /** 237 * Closes this model. This causes the tracked node this model is based upon 238 * to be released (i.e. {@link InMemoryNodeModel#untrackNode(NodeSelector)} 239 * is called). This method should be called when this model is no longer 240 * needed. This implementation is idempotent; it is safe to call 241 * {@code close()} multiple times - only the first invocation has an effect. 242 * After this method has been called this model can no longer be used 243 * because there is no guarantee that the node can still be accessed from 244 * the parent model. 245 */ 246 public void close() 247 { 248 if (closed.compareAndSet(false, true)) 249 { 250 getParentModel().untrackNode(getSelector()); 251 } 252 } 253 254 /** 255 * {@inheritDoc} This implementation calls {@code close()} if the 256 * {@code untrackOnFinalize} flag was set when this instance was 257 * constructed. While this is not 100 percent reliable, it is better than 258 * keeping the tracked node hanging around. Note that it is not a problem if 259 * {@code close()} already had been invoked manually because this method is 260 * idempotent. 261 * 262 * @see #close() 263 */ 264 @Override 265 protected void finalize() throws Throwable 266 { 267 if (isReleaseTrackedNodeOnFinalize()) 268 { 269 close(); 270 } 271 super.finalize(); 272 } 273}