    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}