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 managed by an {@link InMemoryNodeModel} 026 * object as root node. 027 * </p> 028 * <p> 029 * Models of this type are useful when working on specific sub trees of a nodes structure. This is the case for instance 030 * for a {@code SubnodeConfiguration}. 031 * </p> 032 * <p> 033 * An instance of this class is constructed with an {@link InMemoryNodeModelSupport} object providing a reference to the 034 * underlying {@code InMemoryNodeModel} and the {@link NodeSelector} pointing to the tracked node acting as this model's 035 * root node. The {@code NodeModel} operations are implemented by delegating to the wrapped {@code InMemoryNodeModel} 036 * object specifying the selector to the tracked node as target root node for the update transaction. Note that the 037 * tracked node can become detached at any time. This situation is handled transparently by the implementation of 038 * {@code InMemoryNodeModel}. The reason for using an {@code InMemoryNodeModelSupport} object rather than an 039 * {@code InMemoryNodeModel} directly is that this additional layer of indirection can be used for performing special 040 * initializations on the model before it is returned to the {@code TrackedNodeModel} object. This is needed by some 041 * dynamic configuration implementations, e.g. by {@code CombinedConfiguration}. 042 * </p> 043 * <p> 044 * If the tracked node acting as root node is exclusively used by this model, it should be released when this model is 045 * no longer needed. This can be done manually by calling the {@link #close()} method. It is also possible to pass a 046 * value of <strong>true</strong> to the {@code untrackOnFinalize} argument of the constructor. This causes 047 * {@code close()} to be called automatically if this object gets claimed by the garbage collector. 048 * </p> 049 * <p> 050 * As {@code InMemoryNodeModel}, this class is thread-safe. 051 * </p> 052 * 053 * @since 2.0 054 */ 055public class TrackedNodeModel implements NodeModel<ImmutableNode> { 056 /** Stores the underlying parent model. */ 057 private final InMemoryNodeModelSupport parentModelSupport; 058 059 /** The selector for the managed tracked node. */ 060 private final NodeSelector selector; 061 062 /** 063 * A flag whether the tracked not should be released when this object is finalized. 064 */ 065 private final boolean releaseTrackedNodeOnFinalize; 066 067 /** A flag whether this model has already been closed. */ 068 private final AtomicBoolean closed; 069 070 /** 071 * Creates a new instance of {@code TrackedNodeModel} and initializes it with the given underlying model and the 072 * selector to the root node. The boolean argument controls whether the associated tracked node should be released when 073 * this object gets finalized. This allows the underlying model to free some resources. If used as model within a 074 * {@code SubnodeConfiguration}, there is typically no way to discard the model explicitly. Therefore, it makes sense to 075 * do this automatically on finalization. 076 * 077 * @param modelSupport the underlying {@code InMemoryNodeModelSupport} (must not be <b>null</b>) 078 * @param sel the selector to the root node of this model (must not be <b>null</b>) 079 * @param untrackOnFinalize a flag whether the tracked node should be released on finalization 080 * @throws IllegalArgumentException if a required parameter is missing 081 */ 082 public TrackedNodeModel(final InMemoryNodeModelSupport modelSupport, final NodeSelector sel, final boolean untrackOnFinalize) { 083 if (modelSupport == null) { 084 throw new IllegalArgumentException("Underlying model support must not be null!"); 085 } 086 if (sel == null) { 087 throw new IllegalArgumentException("Selector must not be null!"); 088 } 089 090 parentModelSupport = modelSupport; 091 selector = sel; 092 releaseTrackedNodeOnFinalize = untrackOnFinalize; 093 closed = new AtomicBoolean(); 094 } 095 096 @Override 097 public void addNodes(final String key, final Collection<? extends ImmutableNode> nodes, final NodeKeyResolver<ImmutableNode> resolver) { 098 getParentModel().addNodes(key, getSelector(), nodes, resolver); 099 } 100 101 @Override 102 public void addProperty(final String key, final Iterable<?> values, final NodeKeyResolver<ImmutableNode> resolver) { 103 getParentModel().addProperty(key, getSelector(), values, resolver); 104 } 105 106 /** 107 * {@inheritDoc} This implementation clears the sub tree spanned by the associate tracked node. This has the side effect 108 * that this in any case becomes detached. 109 * 110 * @param resolver the {@code NodeKeyResolver}. 111 */ 112 @Override 113 public void clear(final NodeKeyResolver<ImmutableNode> resolver) { 114 getParentModel().clearTree(null, getSelector(), resolver); 115 } 116 117 @Override 118 public void clearProperty(final String key, final NodeKeyResolver<ImmutableNode> resolver) { 119 getParentModel().clearProperty(key, getSelector(), resolver); 120 } 121 122 @Override 123 public List<QueryResult<ImmutableNode>> clearTree(final String key, final NodeKeyResolver<ImmutableNode> resolver) { 124 return getParentModel().clearTree(key, getSelector(), resolver); 125 } 126 127 /** 128 * Closes this model. This causes the tracked node this model is based upon to be released (i.e. 129 * {@link InMemoryNodeModel#untrackNode(NodeSelector)} is called). This method should be called when this model is no 130 * longer needed. This implementation is idempotent; it is safe to call {@code close()} multiple times - only the first 131 * invocation has an effect. After this method has been called this model can no longer be used because there is no 132 * guarantee that the node can still be accessed from the parent model. 133 */ 134 public void close() { 135 if (closed.compareAndSet(false, true)) { 136 getParentModel().untrackNode(getSelector()); 137 } 138 } 139 140 /** 141 * {@inheritDoc} This implementation calls {@code close()} if the {@code untrackOnFinalize} flag was set when this 142 * instance was constructed. While this is not 100 percent reliable, it is better than keeping the tracked node hanging 143 * around. Note that it is not a problem if {@code close()} already had been invoked manually because this method is 144 * idempotent. 145 * 146 * @see #close() 147 */ 148 @Override 149 protected void finalize() throws Throwable { 150 if (isReleaseTrackedNodeOnFinalize()) { 151 close(); 152 } 153 super.finalize(); 154 } 155 156 /** 157 * {@inheritDoc} This implementation returns the tracked node instance acting as root node of this model. 158 */ 159 @Override 160 public ImmutableNode getInMemoryRepresentation() { 161 return getNodeHandler().getRootNode(); 162 } 163 164 @Override 165 public NodeHandler<ImmutableNode> getNodeHandler() { 166 return getParentModel().getTrackedNodeHandler(getSelector()); 167 } 168 169 /** 170 * Gets the parent model. Operations on this model are delegated to this parent model specifying the selector to the 171 * tracked node. 172 * 173 * @return the parent model 174 */ 175 public InMemoryNodeModel getParentModel() { 176 return getParentModelSupport().getNodeModel(); 177 } 178 179 /** 180 * Gets the {@code InMemoryNodeModelSupport} object which is used to gain access to the underlying node model. 181 * 182 * @return the associated {@code InMemoryNodeModelSupport} object 183 */ 184 public InMemoryNodeModelSupport getParentModelSupport() { 185 return parentModelSupport; 186 } 187 188 /** 189 * Gets the {@code NodeSelector} pointing to the tracked node managed by this model. 190 * 191 * @return the tracked node selector 192 */ 193 public NodeSelector getSelector() { 194 return selector; 195 } 196 197 /** 198 * Returns the flag whether the managed tracked node is to be released when this object gets finalized. This method 199 * returns the value of the corresponding flag passed to the constructor. If result is true, the underlying model is 200 * asked to untrack the managed node when this object is claimed by the GC. 201 * 202 * @return a flag whether the managed tracked node should be released when this object dies 203 * @see InMemoryNodeModel#untrackNode(NodeSelector) 204 */ 205 public boolean isReleaseTrackedNodeOnFinalize() { 206 return releaseTrackedNodeOnFinalize; 207 } 208 209 @Override 210 public void setProperty(final String key, final Object value, final NodeKeyResolver<ImmutableNode> resolver) { 211 getParentModel().setProperty(key, getSelector(), value, resolver); 212 } 213 214 @Override 215 public void setRootNode(final ImmutableNode newRoot) { 216 getParentModel().replaceTrackedNode(getSelector(), newRoot); 217 } 218}