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 * @version $Id: TrackedNodeModel.java 1842194 2018-09-27 22:24:23Z ggregory $ 062 * @since 2.0 063 */ 064public class TrackedNodeModel implements NodeModel<ImmutableNode> 065{ 066 /** Stores the underlying parent model. */ 067 private final InMemoryNodeModelSupport parentModelSupport; 068 069 /** The selector for the managed tracked node. */ 070 private final NodeSelector selector; 071 072 /** 073 * A flag whether the tracked not should be released when this object is 074 * finalized. 075 */ 076 private final boolean releaseTrackedNodeOnFinalize; 077 078 /** A flag whether this model has already been closed. */ 079 private final AtomicBoolean closed; 080 081 /** 082 * Creates a new instance of {@code TrackedNodeModel} and initializes it 083 * with the given underlying model and the selector to the root node. The 084 * boolean argument controls whether the associated tracked node should be 085 * released when this object gets finalized. This allows the underlying 086 * model to free some resources. If used as model within a 087 * {@code SubnodeConfiguration}, there is typically no way to discard the 088 * model explicitly. Therefore, it makes sense to do this automatically on 089 * finalization. 090 * 091 * @param modelSupport the underlying {@code InMemoryNodeModelSupport} (must not be 092 * <b>null</b>) 093 * @param sel the selector to the root node of this model (must not be 094 * <b>null</b>) 095 * @param untrackOnFinalize a flag whether the tracked node should be 096 * released on finalization 097 * @throws IllegalArgumentException if a required parameter is missing 098 */ 099 public TrackedNodeModel(final InMemoryNodeModelSupport modelSupport, final NodeSelector sel, 100 final boolean untrackOnFinalize) 101 { 102 if (modelSupport == null) 103 { 104 throw new IllegalArgumentException( 105 "Underlying model support must not be null!"); 106 } 107 if (sel == null) 108 { 109 throw new IllegalArgumentException("Selector must not be null!"); 110 } 111 112 parentModelSupport = modelSupport; 113 selector = sel; 114 releaseTrackedNodeOnFinalize = untrackOnFinalize; 115 closed = new AtomicBoolean(); 116 } 117 118 /** 119 * Returns the {@code InMemoryNodeModelSupport} object which is used to gain 120 * access to the underlying node model. 121 * 122 * @return the associated {@code InMemoryNodeModelSupport} object 123 */ 124 public InMemoryNodeModelSupport getParentModelSupport() 125 { 126 return parentModelSupport; 127 } 128 129 /** 130 * Returns the parent model. Operations on this model are delegated to this 131 * parent model specifying the selector to the tracked node. 132 * 133 * @return the parent model 134 */ 135 public InMemoryNodeModel getParentModel() 136 { 137 return getParentModelSupport().getNodeModel(); 138 } 139 140 /** 141 * Returns the {@code NodeSelector} pointing to the tracked node managed by 142 * this model. 143 * 144 * @return the tracked node selector 145 */ 146 public NodeSelector getSelector() 147 { 148 return selector; 149 } 150 151 /** 152 * Returns the flag whether the managed tracked node is to be released when 153 * this object gets finalized. This method returns the value of the 154 * corresponding flag passed to the constructor. If result is true, the 155 * underlying model is asked to untrack the managed node when this object is 156 * claimed by the GC. 157 * 158 * @return a flag whether the managed tracked node should be released when 159 * this object dies 160 * @see InMemoryNodeModel#untrackNode(NodeSelector) 161 */ 162 public boolean isReleaseTrackedNodeOnFinalize() 163 { 164 return releaseTrackedNodeOnFinalize; 165 } 166 167 @Override 168 public void setRootNode(final ImmutableNode newRoot) 169 { 170 getParentModel().replaceTrackedNode(getSelector(), newRoot); 171 } 172 173 @Override 174 public NodeHandler<ImmutableNode> getNodeHandler() 175 { 176 return getParentModel().getTrackedNodeHandler(getSelector()); 177 } 178 179 @Override 180 public void addProperty(final String key, final Iterable<?> values, 181 final NodeKeyResolver<ImmutableNode> resolver) 182 { 183 getParentModel().addProperty(key, getSelector(), values, resolver); 184 } 185 186 @Override 187 public void addNodes(final String key, final Collection<? extends ImmutableNode> nodes, 188 final NodeKeyResolver<ImmutableNode> resolver) 189 { 190 getParentModel().addNodes(key, getSelector(), nodes, resolver); 191 } 192 193 @Override 194 public void setProperty(final String key, final Object value, 195 final NodeKeyResolver<ImmutableNode> resolver) 196 { 197 getParentModel().setProperty(key, getSelector(), value, resolver); 198 } 199 200 @Override 201 public List<QueryResult<ImmutableNode>> clearTree(final String key, 202 final NodeKeyResolver<ImmutableNode> resolver) 203 { 204 return getParentModel().clearTree(key, getSelector(), resolver); 205 } 206 207 @Override 208 public void clearProperty(final String key, 209 final NodeKeyResolver<ImmutableNode> resolver) 210 { 211 getParentModel().clearProperty(key, getSelector(), resolver); 212 } 213 214 /** 215 * {@inheritDoc} This implementation clears the sub tree spanned by the 216 * associate tracked node. This has the side effect that this in any case 217 * becomes detached. 218 * 219 * @param resolver 220 */ 221 @Override 222 public void clear(final NodeKeyResolver<ImmutableNode> resolver) 223 { 224 getParentModel().clearTree(null, getSelector(), resolver); 225 } 226 227 /** 228 * {@inheritDoc} This implementation returns the tracked node instance 229 * acting as root node of this model. 230 */ 231 @Override 232 public ImmutableNode getInMemoryRepresentation() 233 { 234 return getNodeHandler().getRootNode(); 235 } 236 237 /** 238 * Closes this model. This causes the tracked node this model is based upon 239 * to be released (i.e. {@link InMemoryNodeModel#untrackNode(NodeSelector)} 240 * is called). This method should be called when this model is no longer 241 * needed. This implementation is idempotent; it is safe to call 242 * {@code close()} multiple times - only the first invocation has an effect. 243 * After this method has been called this model can no longer be used 244 * because there is no guarantee that the node can still be accessed from 245 * the parent model. 246 */ 247 public void close() 248 { 249 if (closed.compareAndSet(false, true)) 250 { 251 getParentModel().untrackNode(getSelector()); 252 } 253 } 254 255 /** 256 * {@inheritDoc} This implementation calls {@code close()} if the 257 * {@code untrackOnFinalize} flag was set when this instance was 258 * constructed. While this is not 100 percent reliable, it is better than 259 * keeping the tracked node hanging around. Note that it is not a problem if 260 * {@code close()} already had been invoked manually because this method is 261 * idempotent. 262 * 263 * @see #close() 264 */ 265 @Override 266 protected void finalize() throws Throwable 267 { 268 if (isReleaseTrackedNodeOnFinalize()) 269 { 270 close(); 271 } 272 super.finalize(); 273 } 274}