Package org.apache.commons.configuration2

Class SubnodeConfiguration

java.lang.Object
org.apache.commons.configuration2.event.BaseEventSource
org.apache.commons.configuration2.AbstractConfiguration
org.apache.commons.configuration2.AbstractHierarchicalConfiguration<ImmutableNode>
org.apache.commons.configuration2.BaseHierarchicalConfiguration
org.apache.commons.configuration2.SubnodeConfiguration
All Implemented Interfaces:
Cloneable, Configuration, EventSource, HierarchicalConfiguration<ImmutableNode>, ImmutableConfiguration, ImmutableHierarchicalConfiguration, SynchronizerSupport, InMemoryNodeModelSupport, NodeKeyResolver<ImmutableNode>, NodeModelSupport<ImmutableNode>
public class SubnodeConfiguration extends BaseHierarchicalConfiguration

A specialized hierarchical configuration class with a node model that uses a tracked node of another node model as its root node.

Configurations of this type are initialized with a special NodeModel operating on a specific tracked node of the parent configuration and the corresponding NodeSelector. All property accessor methods are evaluated relative to this root node. A good use case for a SubnodeConfiguration is when multiple properties from a specific sub tree of the whole configuration need to be accessed. Then a 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.

By making use of a tracked node as root node, a 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 SubnodeConfiguration if the sub tree spanned by the SubnodeConfiguration's root node is involved.

Note that by making use of a NodeSelector the 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 SubnodeConfiguration still references the element with index 2 which is now another one.

There are also possible changes of the underlying nodes structure which completely detach the SubnodeConfiguration from its parent configuration. For instance, the key referenced by the SubnodeConfiguration could be removed in the parent configuration. If this happens, the 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).

When a subnode configuration is created, it inherits the settings of its parent configuration, e.g. some flags like the 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.

Because the SubnodeConfiguration operates on the same nodes structure as its parent it uses the same Synchronizer instance per default. This means that locks held on one SubnodeConfiguration also impact the parent configuration and all of its other 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.

From its purpose this class is quite similar to 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 SubsetConfiguration because creating a subset configuration is more expensive than creating a subnode configuration.

It is strongly recommended to create SubnodeConfiguration instances only through the 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.

Since:
1.3

  • Constructor Details

  • Method Details

    • cloneNodeModel

      protected NodeModel<ImmutableNode> cloneNodeModel()
      Creates a clone of the node model. This method is called by clone(). This implementation creates a new instance of InMemoryNodeModel, initialized with this configuration's root node. This has the effect that although the same nodes are used, the original and copied configurations are independent on each other. 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.
      Overrides:
      cloneNodeModel in class BaseHierarchicalConfiguration
      Returns:
      the node model for the clone

    • close

      public void close()
      Closes this sub configuration. This method closes the underlying 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.

    • createSubConfigurationForTrackedNode

      protected SubnodeConfiguration createSubConfigurationForTrackedNode(NodeSelector selector, InMemoryNodeModelSupport parentModelSupport)
      Creates a connected sub configuration based on a selector for a tracked node. This implementation makes sure that the correct node model (the one of the parent) is used for the new sub configuration.
      Overrides:
      createSubConfigurationForTrackedNode in class BaseHierarchicalConfiguration
      Parameters:
      selector - the NodeSelector
      parentModelSupport - the InMemoryNodeModelSupport object for the parent node model
      Returns:
      the newly created sub configuration

    • getNodeModel

      public InMemoryNodeModel getNodeModel()
      Gets the NodeModel supported by this object. This implementation returns the configuration's NodeModel. It is guarded by the current Synchronizer. This implementation returns the InMemoryNodeModel used by this configuration. 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 SubnodeConfiguration. Be aware that the implementation of this method is not very efficient.
      Specified by:
      getNodeModel in interface InMemoryNodeModelSupport
      Specified by:
      getNodeModel in interface NodeModelSupport<ImmutableNode>
      Overrides:
      getNodeModel in class BaseHierarchicalConfiguration
      Returns:
      the NodeModel

    • getParent

      public BaseHierarchicalConfiguration getParent()
      Gets the parent configuration of this subnode configuration.
      Returns:
      the parent configuration

    • getRootNodeModel

      public InMemoryNodeModel getRootNodeModel()
      Gets the node model of the root configuration. 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 SubnodeConfiguration has been created from another SubnodeConfiguration.
      Returns:
      the root node model
      Since:
      2.2

    • getRootSelector

      public NodeSelector getRootSelector()
      Gets the selector to the root node of this configuration.
      Returns:
      the NodeSelector to the root node

    • getSubConfigurationNodeSelector

      protected NodeSelector getSubConfigurationNodeSelector(String key)
      Gets the NodeSelector to be used for a sub configuration based on the passed in key. This method is called whenever a sub configuration is to be created. This base implementation returns a new NodeSelector initialized with the passed in key. Sub classes may override this method if they have a different strategy for creating a selector. This implementation returns a sub selector of the selector of this configuration.
      Overrides:
      getSubConfigurationNodeSelector in class BaseHierarchicalConfiguration
      Parameters:
      key - the key of the sub configuration
      Returns:
      a NodeSelector for initializing a sub configuration

    • getSubConfigurationParentModel

      protected InMemoryNodeModel getSubConfigurationParentModel()
      Gets the InMemoryNodeModel to be used as parent model for a new sub configuration. This method is called whenever a sub configuration is to be created. This base implementation returns the model of this configuration. Sub classes with different requirements for the parent models of sub configurations have to override it. This implementation returns the parent model of the TrackedNodeModel used by this configuration.
      Overrides:
      getSubConfigurationParentModel in class BaseHierarchicalConfiguration
      Returns:
      the parent model for a new sub configuration