SubnodeConfiguration.java
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* 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
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*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
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package org.apache.commons.configuration2;
import org.apache.commons.configuration2.tree.ImmutableNode;
import org.apache.commons.configuration2.tree.InMemoryNodeModel;
import org.apache.commons.configuration2.tree.InMemoryNodeModelSupport;
import org.apache.commons.configuration2.tree.NodeModel;
import org.apache.commons.configuration2.tree.NodeSelector;
import org.apache.commons.configuration2.tree.TrackedNodeModel;
/**
* <p>
* A specialized hierarchical configuration class with a node model that uses a tracked node of another node model as
* its root node.
* </p>
* <p>
* Configurations of this type are initialized with a special {@link NodeModel} operating on a specific tracked node of
* the parent configuration and the corresponding {@link NodeSelector}. All property accessor methods are evaluated
* relative to this root node. A good use case for a {@code SubnodeConfiguration} is when multiple properties from a
* specific sub tree of the whole configuration need to be accessed. Then a {@code SubnodeConfiguration} can be created
* with the parent node of the affected sub tree as root node. This allows for simpler property keys and is also more
* efficient.
* </p>
* <p>
* By making use of a tracked node as root node, a {@code SubnodeConfiguration} and its parent configuration initially
* operate on the same hierarchy of configuration nodes. So if modifications are performed at the subnode configuration,
* these changes are immediately visible in the parent configuration. Analogously will updates of the parent
* configuration affect the {@code SubnodeConfiguration} if the sub tree spanned by the {@code SubnodeConfiguration}'s
* root node is involved.
* </p>
* <p>
* Note that by making use of a {@code NodeSelector} the {@code SubnodeConfiguration} is not associated with a physical
* node instance, but the selection criteria stored in the selector are evaluated after each change of the nodes
* structure. As an example consider that the selector uses a key with an index into a list element, say index 2. Now if
* an update occurs on the underlying nodes structure which removes the first element in this list structure, the
* {@code SubnodeConfiguration} still references the element with index 2 which is now another one.
* </p>
* <p>
* There are also possible changes of the underlying nodes structure which completely detach the
* {@code SubnodeConfiguration} from its parent configuration. For instance, the key referenced by the
* {@code SubnodeConfiguration} could be removed in the parent configuration. If this happens, the
* {@code SubnodeConfiguration} stays functional; however, it now operates on a separate node model than its parent
* configuration. Changes made by one configuration are no longer visible for the other one (as the node models have no
* longer overlapping nodes, there is no way to have a synchronization here).
* </p>
* <p>
* When a subnode configuration is created, it inherits the settings of its parent configuration, e.g. some flags like
* the {@code throwExceptionOnMissing} flag or the settings for handling list delimiters) or the expression engine. If
* these settings are changed later in either the subnode or the parent configuration, the changes are not visible for
* each other. So you could create a subnode configuration, and change its expression engine without affecting the
* parent configuration.
* </p>
* <p>
* Because the {@code SubnodeConfiguration} operates on the same nodes structure as its parent it uses the same
* {@code Synchronizer} instance per default. This means that locks held on one {@code SubnodeConfiguration} also impact
* the parent configuration and all of its other {@code SubnodeConfiguration} objects. You should not change this
* without a good reason! Otherwise, there is the risk of data corruption when multiple threads access these
* configuration concurrently.
* </p>
* <p>
* From its purpose this class is quite similar to {@link SubsetConfiguration}. The difference is that a subset
* configuration of a hierarchical configuration may combine multiple configuration nodes from different sub trees of
* the configuration, while all nodes in a subnode configuration belong to the same sub tree. If an application can live
* with this limitation, it is recommended to use this class instead of {@code SubsetConfiguration} because creating a
* subset configuration is more expensive than creating a subnode configuration.
* </p>
* <p>
* It is strongly recommended to create {@code SubnodeConfiguration} instances only through the
* {@code configurationAt()} methods of a hierarchical configuration. These methods ensure that all necessary
* initializations are done. Creating instances manually without doing proper initialization may break some of the
* functionality provided by this class.
* </p>
*
* @since 1.3
*/
public class SubnodeConfiguration extends BaseHierarchicalConfiguration {
/** Stores the parent configuration. */
private final BaseHierarchicalConfiguration parent;
/** The node selector selecting the root node of this configuration. */
private final NodeSelector rootSelector;
/**
* Creates a new instance of {@code SubnodeConfiguration} and initializes it with all relevant properties.
*
* @param parent the parent configuration
* @param model the {@code TrackedNodeModel} to be used for this configuration
* @throws IllegalArgumentException if a required argument is missing
*/
public SubnodeConfiguration(final BaseHierarchicalConfiguration parent, final TrackedNodeModel model) {
super(model);
if (parent == null) {
throw new IllegalArgumentException("Parent configuration must not be null!");
}
if (model == null) {
throw new IllegalArgumentException("Node model must not be null!");
}
this.parent = parent;
rootSelector = model.getSelector();
}
/**
* {@inheritDoc} This implementation returns a copy of the current node model with the same settings. However, it has to
* be ensured that the track count for the node selector is increased.
*
* @return the node model for the clone
*/
@Override
protected NodeModel<ImmutableNode> cloneNodeModel() {
final InMemoryNodeModel parentModel = (InMemoryNodeModel) getParent().getModel();
parentModel.trackNode(getRootSelector(), getParent());
return new TrackedNodeModel(getParent(), getRootSelector(), true);
}
/**
* Closes this sub configuration. This method closes the underlying {@link TrackedNodeModel}, thus causing the tracked
* node acting as root node to be released. Per default, this happens automatically when the model is claimed by the
* garbage collector. By calling this method explicitly, it can be indicated that this configuration is no longer used
* and that resources used by it can be freed immediately.
*/
public void close() {
getTrackedModel().close();
}
/**
* {@inheritDoc} This implementation makes sure that the correct node model (the one of the parent) is used for the new
* sub configuration.
*/
@Override
protected SubnodeConfiguration createSubConfigurationForTrackedNode(final NodeSelector selector, final InMemoryNodeModelSupport parentModelSupport) {
return super.createSubConfigurationForTrackedNode(selector, getParent());
}
/**
* {@inheritDoc} This implementation returns a newly created node model with the correct root node set. Note that this
* model is not used for property access, but only made available to clients that need to operate on the node structure
* of this {@code SubnodeConfiguration}. Be aware that the implementation of this method is not very efficient.
*/
@Override
public InMemoryNodeModel getNodeModel() {
final ImmutableNode root = getParent().getNodeModel().getTrackedNode(getRootSelector());
return new InMemoryNodeModel(root);
}
/**
* Gets the parent configuration of this subnode configuration.
*
* @return the parent configuration
*/
public BaseHierarchicalConfiguration getParent() {
return parent;
}
/**
* Gets the node model of the root configuration. {@code SubnodeConfiguration} instances created from a hierarchical
* configuration operate on the same node model, using different nodes as their local root nodes. With this method the
* top-level node model can be obtained. It works even in constellations where a {@code SubnodeConfiguration} has been
* created from another {@code SubnodeConfiguration}.
*
* @return the root node model
* @since 2.2
*/
public InMemoryNodeModel getRootNodeModel() {
if (getParent() instanceof SubnodeConfiguration) {
return ((SubnodeConfiguration) getParent()).getRootNodeModel();
}
return getParent().getNodeModel();
}
/**
* Gets the selector to the root node of this configuration.
*
* @return the {@code NodeSelector} to the root node
*/
public NodeSelector getRootSelector() {
return rootSelector;
}
/**
* {@inheritDoc} This implementation returns a sub selector of the selector of this configuration.
*/
@Override
protected NodeSelector getSubConfigurationNodeSelector(final String key) {
return getRootSelector().subSelector(key);
}
/**
* {@inheritDoc} This implementation returns the parent model of the {@link TrackedNodeModel} used by this
* configuration.
*/
@Override
protected InMemoryNodeModel getSubConfigurationParentModel() {
return getTrackedModel().getParentModel();
}
/**
* Convenience method that returns the tracked model used by this sub configuration.
*
* @return the {@code TrackedNodeModel}
*/
private TrackedNodeModel getTrackedModel() {
return (TrackedNodeModel) getModel();
}
}