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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();
}
/**
* Returns 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;
}
/**
* Returns 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();
}
/**
* Returns 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 setRootNode(final ImmutableNode newRoot)
{
getParentModel().replaceTrackedNode(getSelector(), newRoot);
}
@Override
public NodeHandler getNodeHandler()
{
return getParentModel().getTrackedNodeHandler(getSelector());
}
@Override
public void addProperty(final String key, final Iterable values,
final NodeKeyResolver resolver)
{
getParentModel().addProperty(key, getSelector(), values, resolver);
}
@Override
public void addNodes(final String key, final Collection nodes,
final NodeKeyResolver resolver)
{
getParentModel().addNodes(key, getSelector(), nodes, resolver);
}
@Override
public void setProperty(final String key, final Object value,
final NodeKeyResolver resolver)
{
getParentModel().setProperty(key, getSelector(), value, resolver);
}
@Override
public List> clearTree(final String key,
final NodeKeyResolver resolver)
{
return getParentModel().clearTree(key, getSelector(), resolver);
}
@Override
public void clearProperty(final String key,
final NodeKeyResolver resolver)
{
getParentModel().clearProperty(key, getSelector(), 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
*/
@Override
public void clear(final NodeKeyResolver resolver)
{
getParentModel().clearTree(null, getSelector(), resolver);
}
/**
* {@inheritDoc} This implementation returns the tracked node instance
* acting as root node of this model.
*/
@Override
public ImmutableNode getInMemoryRepresentation()
{
return getNodeHandler().getRootNode();
}
/**
* 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();
}
}