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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.configuration2.tree;
import java.util.Collection;
import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;
/**
*
* A specialized {@code NodeModel} implementation that uses a tracked node managed by an {@link InMemoryNodeModel}
* object as root node.
*
*
* Models of this type are useful when working on specific sub trees of a nodes structure. This is the case for instance
* for a {@code SubnodeConfiguration}.
*
*
* An instance of this class is constructed with an {@link InMemoryNodeModelSupport} object providing a reference to the
* underlying {@code InMemoryNodeModel} and the {@link NodeSelector} pointing to the tracked node acting as this model's
* root node. The {@code NodeModel} operations are implemented by delegating to the wrapped {@code InMemoryNodeModel}
* object specifying the selector to the tracked node as target root node for the update transaction. Note that the
* tracked node can become detached at any time. This situation is handled transparently by the implementation of
* {@code InMemoryNodeModel}. The reason for using an {@code InMemoryNodeModelSupport} object rather than an
* {@code InMemoryNodeModel} directly is that this additional layer of indirection can be used for performing special
* initializations on the model before it is returned to the {@code TrackedNodeModel} object. This is needed by some
* dynamic configuration implementations, e.g. by {@code CombinedConfiguration}.
*
*
* If the tracked node acting as root node is exclusively used by this model, it should be released when this model is
* no longer needed. This can be done manually by calling the {@link #close()} method. It is also possible to pass a
* value of true to the {@code untrackOnFinalize} argument of the constructor. This causes
* {@code close()} to be called automatically if this object gets claimed by the garbage collector.
*
*
* As {@code InMemoryNodeModel}, this class is thread-safe.
*
*
* @since 2.0
*/
public class TrackedNodeModel implements NodeModel {
/** Stores the underlying parent model. */
private final InMemoryNodeModelSupport parentModelSupport;
/** The selector for the managed tracked node. */
private final NodeSelector selector;
/**
* A flag whether the tracked not should be released when this object is finalized.
*/
private final boolean releaseTrackedNodeOnFinalize;
/** A flag whether this model has already been closed. */
private final AtomicBoolean closed;
/**
* Creates a new instance of {@code TrackedNodeModel} and initializes it with the given underlying model and the
* selector to the root node. The boolean argument controls whether the associated tracked node should be released when
* this object gets finalized. This allows the underlying model to free some resources. If used as model within a
* {@code SubnodeConfiguration}, there is typically no way to discard the model explicitly. Therefore, it makes sense to
* do this automatically on finalization.
*
* @param modelSupport the underlying {@code InMemoryNodeModelSupport} (must not be null)
* @param sel the selector to the root node of this model (must not be null)
* @param untrackOnFinalize a flag whether the tracked node should be released on finalization
* @throws IllegalArgumentException if a required parameter is missing
*/
public TrackedNodeModel(final InMemoryNodeModelSupport modelSupport, final NodeSelector sel, final boolean untrackOnFinalize) {
if (modelSupport == null) {
throw new IllegalArgumentException("Underlying model support must not be null!");
}
if (sel == null) {
throw new IllegalArgumentException("Selector must not be null!");
}
parentModelSupport = modelSupport;
selector = sel;
releaseTrackedNodeOnFinalize = untrackOnFinalize;
closed = new AtomicBoolean();
}
@Override
public void addNodes(final String key, final Collection nodes, final NodeKeyResolver resolver) {
getParentModel().addNodes(key, getSelector(), nodes, resolver);
}
@Override
public void addProperty(final String key, final Iterable values, final NodeKeyResolver resolver) {
getParentModel().addProperty(key, getSelector(), values, resolver);
}
/**
* {@inheritDoc} This implementation clears the sub tree spanned by the associate tracked node. This has the side effect
* that this in any case becomes detached.
*
* @param resolver the {@code NodeKeyResolver}.
*/
@Override
public void clear(final NodeKeyResolver resolver) {
getParentModel().clearTree(null, getSelector(), resolver);
}
@Override
public void clearProperty(final String key, final NodeKeyResolver resolver) {
getParentModel().clearProperty(key, getSelector(), resolver);
}
@Override
public List> clearTree(final String key, final NodeKeyResolver resolver) {
return getParentModel().clearTree(key, getSelector(), resolver);
}
/**
* Closes this model. This causes the tracked node this model is based upon to be released (i.e.
* {@link InMemoryNodeModel#untrackNode(NodeSelector)} is called). This method should be called when this model is no
* longer needed. This implementation is idempotent; it is safe to call {@code close()} multiple times - only the first
* invocation has an effect. After this method has been called this model can no longer be used because there is no
* guarantee that the node can still be accessed from the parent model.
*/
public void close() {
if (closed.compareAndSet(false, true)) {
getParentModel().untrackNode(getSelector());
}
}
/**
* {@inheritDoc} This implementation calls {@code close()} if the {@code untrackOnFinalize} flag was set when this
* instance was constructed. While this is not 100 percent reliable, it is better than keeping the tracked node hanging
* around. Note that it is not a problem if {@code close()} already had been invoked manually because this method is
* idempotent.
*
* @see #close()
*/
@Override
protected void finalize() throws Throwable {
if (isReleaseTrackedNodeOnFinalize()) {
close();
}
super.finalize();
}
/**
* {@inheritDoc} This implementation returns the tracked node instance acting as root node of this model.
*/
@Override
public ImmutableNode getInMemoryRepresentation() {
return getNodeHandler().getRootNode();
}
@Override
public NodeHandler getNodeHandler() {
return getParentModel().getTrackedNodeHandler(getSelector());
}
/**
* Gets the parent model. Operations on this model are delegated to this parent model specifying the selector to the
* tracked node.
*
* @return the parent model
*/
public InMemoryNodeModel getParentModel() {
return getParentModelSupport().getNodeModel();
}
/**
* Gets the {@code InMemoryNodeModelSupport} object which is used to gain access to the underlying node model.
*
* @return the associated {@code InMemoryNodeModelSupport} object
*/
public InMemoryNodeModelSupport getParentModelSupport() {
return parentModelSupport;
}
/**
* Gets the {@code NodeSelector} pointing to the tracked node managed by this model.
*
* @return the tracked node selector
*/
public NodeSelector getSelector() {
return selector;
}
/**
* Returns the flag whether the managed tracked node is to be released when this object gets finalized. This method
* returns the value of the corresponding flag passed to the constructor. If result is true, the underlying model is
* asked to untrack the managed node when this object is claimed by the GC.
*
* @return a flag whether the managed tracked node should be released when this object dies
* @see InMemoryNodeModel#untrackNode(NodeSelector)
*/
public boolean isReleaseTrackedNodeOnFinalize() {
return releaseTrackedNodeOnFinalize;
}
@Override
public void setProperty(final String key, final Object value, final NodeKeyResolver resolver) {
getParentModel().setProperty(key, getSelector(), value, resolver);
}
@Override
public void setRootNode(final ImmutableNode newRoot) {
getParentModel().replaceTrackedNode(getSelector(), newRoot);
}
}