    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    /**
    097     * Returns the {@code InMemoryNodeModelSupport} object which is used to gain access to the underlying node model.
    098     *
    099     * @return the associated {@code InMemoryNodeModelSupport} object
    100     */
    101    public InMemoryNodeModelSupport getParentModelSupport() {
    102        return parentModelSupport;
    103    }
    104
    105    /**
    106     * Returns the parent model. Operations on this model are delegated to this parent model specifying the selector to the
    107     * tracked node.
    108     *
    109     * @return the parent model
    110     */
    111    public InMemoryNodeModel getParentModel() {
    112        return getParentModelSupport().getNodeModel();
    113    }
    114
    115    /**
    116     * Returns the {@code NodeSelector} pointing to the tracked node managed by this model.
    117     *
    118     * @return the tracked node selector
    119     */
    120    public NodeSelector getSelector() {
    121        return selector;
    122    }
    123
    124    /**
    125     * Returns the flag whether the managed tracked node is to be released when this object gets finalized. This method
    126     * returns the value of the corresponding flag passed to the constructor. If result is true, the underlying model is
    127     * asked to untrack the managed node when this object is claimed by the GC.
    128     *
    129     * @return a flag whether the managed tracked node should be released when this object dies
    130     * @see InMemoryNodeModel#untrackNode(NodeSelector)
    131     */
    132    public boolean isReleaseTrackedNodeOnFinalize() {
    133        return releaseTrackedNodeOnFinalize;
    134    }
    135
    136    @Override
    137    public void setRootNode(final ImmutableNode newRoot) {
    138        getParentModel().replaceTrackedNode(getSelector(), newRoot);
    139    }
    140
    141    @Override
    142    public NodeHandler<ImmutableNode> getNodeHandler() {
    143        return getParentModel().getTrackedNodeHandler(getSelector());
    144    }
    145
    146    @Override
    147    public void addProperty(final String key, final Iterable<?> values, final NodeKeyResolver<ImmutableNode> resolver) {
    148        getParentModel().addProperty(key, getSelector(), values, resolver);
    149    }
    150
    151    @Override
    152    public void addNodes(final String key, final Collection<? extends ImmutableNode> nodes, final NodeKeyResolver<ImmutableNode> resolver) {
    153        getParentModel().addNodes(key, getSelector(), nodes, resolver);
    154    }
    155
    156    @Override
    157    public void setProperty(final String key, final Object value, final NodeKeyResolver<ImmutableNode> resolver) {
    158        getParentModel().setProperty(key, getSelector(), value, resolver);
    159    }
    160
    161    @Override
    162    public List<QueryResult<ImmutableNode>> clearTree(final String key, final NodeKeyResolver<ImmutableNode> resolver) {
    163        return getParentModel().clearTree(key, getSelector(), resolver);
    164    }
    165
    166    @Override
    167    public void clearProperty(final String key, final NodeKeyResolver<ImmutableNode> resolver) {
    168        getParentModel().clearProperty(key, getSelector(), resolver);
    169    }
    170
    171    /**
    172     * {@inheritDoc} This implementation clears the sub tree spanned by the associate tracked node. This has the side effect
    173     * that this in any case becomes detached.
    174     *
    175     * @param resolver the {@code NodeKeyResolver}.
    176     */
    177    @Override
    178    public void clear(final NodeKeyResolver<ImmutableNode> resolver) {
    179        getParentModel().clearTree(null, getSelector(), resolver);
    180    }
    181
    182    /**
    183     * {@inheritDoc} This implementation returns the tracked node instance acting as root node of this model.
    184     */
    185    @Override
    186    public ImmutableNode getInMemoryRepresentation() {
    187        return getNodeHandler().getRootNode();
    188    }
    189
    190    /**
    191     * Closes this model. This causes the tracked node this model is based upon to be released (i.e.
    192     * {@link InMemoryNodeModel#untrackNode(NodeSelector)} is called). This method should be called when this model is no
    193     * longer needed. This implementation is idempotent; it is safe to call {@code close()} multiple times - only the first
    194     * invocation has an effect. After this method has been called this model can no longer be used because there is no
    195     * guarantee that the node can still be accessed from the parent model.
    196     */
    197    public void close() {
    198        if (closed.compareAndSet(false, true)) {
    199            getParentModel().untrackNode(getSelector());
    200        }
    201    }
    202
    203    /**
    204     * {@inheritDoc} This implementation calls {@code close()} if the {@code untrackOnFinalize} flag was set when this
    205     * instance was constructed. While this is not 100 percent reliable, it is better than keeping the tracked node hanging
    206     * around. Note that it is not a problem if {@code close()} already had been invoked manually because this method is
    207     * idempotent.
    208     *
    209     * @see #close()
    210     */
    211    @Override
    212    protected void finalize() throws Throwable {
    213        if (isReleaseTrackedNodeOnFinalize()) {
    214            close();
    215        }
    216        super.finalize();
    217    }
    218}