org.apache.commons.configuration

Class HierarchicalConfiguration

public class HierarchicalConfiguration extends AbstractConfiguration implements Serializable, Cloneable

A specialized configuration class that extends its base class by the ability of keeping more structure in the stored properties.

There are some sources of configuration data that cannot be stored very well in a BaseConfiguration object because then their structure is lost. This is especially true for XML documents. This class can deal with such structured configuration sources by storing the properties in a tree-like organization.

The internal used storage form allows for a more sophisticated access to single properties. As an example consider the following XML document:

 <database>
   <tables>
     <table>
       <name>users</name>
       <fields>
         <field>
           <name>lid</name>
           <type>long</name>
         </field>
         <field>
           <name>usrName</name>
           <type>java.lang.String</type>
         </field>
        ...
       </fields>
     </table>
     <table>
       <name>documents</name>
       <fields>
         <field>
           <name>docid</name>
           <type>long</type>
         </field>
         ...
       </fields>
     </table>
     ...
   </tables>
 </database>
 

If this document is parsed and stored in a HierarchicalConfiguration object (which can be done by one of the sub classes), there are enhanced possibilities of accessing properties. The keys for querying information can contain indices that select a certain element if there are multiple hits.

For instance the key tables.table(0).name can be used to find out the name of the first table. In opposite tables.table.name would return a collection with the names of all available tables. Similarily the key tables.table(1).fields.field.name returns a collection with the names of all fields of the second table. If another index is added after the field element, a single field can be accessed: tables.table(1).fields.field(0).name.

There is a getMaxIndex() method that returns the maximum allowed index that can be added to a given property key. This method can be used to iterate over all values defined for a certain property.

Version: $Id: HierarchicalConfiguration.java,v 1.14 2004/12/02 22:05:52 ebourg Exp $

Author: Oliver Heger

Nested Class Summary
protected abstract static classHierarchicalConfiguration.BuilderVisitor
A specialized visitor base class that can be used for storing the tree of configuration nodes.
static classHierarchicalConfiguration.CloneVisitor
A specialized visitor that is able to create a deep copy of a node hierarchy.
classHierarchicalConfiguration.DefinedKeysVisitor
A specialized visitor that fills a list with keys that are defined in a node hierarchy.
static classHierarchicalConfiguration.DefinedVisitor
A specialized visitor that checks if a node is defined.
static classHierarchicalConfiguration.Node
A data class for storing (hierarchical) property information.
static classHierarchicalConfiguration.NodeVisitor

Definition of a visitor class for traversing a node and all of its children.

This class defines the interface of a visitor for Node objects and provides a default implementation.

Field Summary
static ExpressionEnginedefaultExpressionEngine
Stores the default expression engine to be used for new objects.
ExpressionEngineexpressionEngine
Stores the expression engine for this instance.
static intEVENT_ADD_NODES
Constant for the add nodes event.
static intEVENT_CLEAR_TREE
Constant for the clear tree event.
HierarchicalConfiguration.Noderoot
Stores the root node of this configuration.
ConfigurationNoderootNode
Stores the root configuration node.
static longserialVersionUID
The serial version UID.
Constructor Summary
HierarchicalConfiguration()
Creates a new instance of HierarchicalConfiguration.
HierarchicalConfiguration(HierarchicalConfiguration c)
Creates a new instance of HierarchicalConfiguration and copies all data contained in the specified configuration into the new one.
Method Summary
voidaddNodes(String key, Collection nodes)
Adds a collection of nodes at the specified position of the configuration tree.
protected voidaddPropertyDirect(String key, Object obj)
Adds the property with the specified key.
protected voidclearNode(HierarchicalConfiguration.Node node)
Clears the value of the specified node.
protected voidclearNode(ConfigurationNode node)
Clears the value of the specified node.
voidclearProperty(String key)
Removes the property with the given key.
protected static voidclearReferences(ConfigurationNode node)
Clears all reference fields in a node structure.
voidclearTree(String key)
Removes all values of the property with the given name and of keys that start with this name.
Objectclone()
Creates a copy of this object.
SubnodeConfigurationconfigurationAt(String key)

Returns a hierarchical subnode configuration object that wraps the configuration node specified by the given key.

ListconfigurationsAt(String key)
Returns a list of sub configurations for all configuration nodes selected by the given key.
booleancontainsKey(String key)
Checks if the specified key is contained in this configuration.
protected HierarchicalConfiguration.NodecreateAddPath(ConfigurationKey.KeyIterator keyIt, HierarchicalConfiguration.Node root)
Creates the missing nodes for adding a new property.
protected HierarchicalConfiguration.NodecreateNode(String name)
Creates a new Node object with the specified name.
protected SubnodeConfigurationcreateSubnodeConfiguration(ConfigurationNode node)
Creates a subnode configuration for the specified node.
protected HierarchicalConfiguration.NodefetchAddNode(ConfigurationKey.KeyIterator keyIt, HierarchicalConfiguration.Node startNode)
Returns a reference to the parent node of an add operation.
protected ListfetchNodeList(String key)
Helper method for fetching a list of all nodes that are addressed by the specified key.
protected HierarchicalConfiguration.NodefindLastPathNode(ConfigurationKey.KeyIterator keyIt, HierarchicalConfiguration.Node node)
Finds the last existing node for an add operation.
protected voidfindPropertyNodes(ConfigurationKey.KeyIterator keyPart, HierarchicalConfiguration.Node node, Collection nodes)
Recursive helper method for fetching a property.
static ExpressionEnginegetDefaultExpressionEngine()
Returns the default expression engine.
ExpressionEnginegetExpressionEngine()
Returns the expression engine used by this configuration.
IteratorgetKeys()
Returns an iterator with all keys defined in this configuration.
IteratorgetKeys(String prefix)
Returns an iterator with all keys defined in this configuration that start with the given prefix.
intgetMaxIndex(String key)
Returns the maximum defined index for the given key.
ObjectgetProperty(String key)
Fetches the specified property.
HierarchicalConfiguration.NodegetRoot()
Returns the root node of this hierarchical configuration.
ConfigurationNodegetRootNode()
Returns the root node of this hierarchical configuration.
booleanisEmpty()
Checks if this configuration is empty.
protected booleannodeDefined(HierarchicalConfiguration.Node node)
Checks if the specified node is defined.
protected booleannodeDefined(ConfigurationNode node)
Checks if the specified node is defined.
ConfigurationNodeprocessNodeAddData(NodeAddData data)
Helper method for processing a node add data object obtained from the expression engine.
protected voidremoveNode(HierarchicalConfiguration.Node node)
Removes the specified node from this configuration.
protected voidremoveNode(ConfigurationNode node)
Removes the specified node from this configuration.
static voidsetDefaultExpressionEngine(ExpressionEngine engine)
Sets the default expression engine.
voidsetExpressionEngine(ExpressionEngine expressionEngine)
Sets the expression engine to be used by this configuration.
voidsetProperty(String key, Object value)
Sets the value of the specified property.
voidsetRoot(HierarchicalConfiguration.Node node)
Sets the root node of this hierarchical configuration.
voidsetRootNode(ConfigurationNode rootNode)
Sets the root node of this hierarchical configuration.
Configurationsubset(String prefix)
Creates a new Configuration object containing all keys that start with the specified prefix.

Field Detail

defaultExpressionEngine

private static ExpressionEngine defaultExpressionEngine
Stores the default expression engine to be used for new objects.

expressionEngine

private ExpressionEngine expressionEngine
Stores the expression engine for this instance.

EVENT_ADD_NODES

public static final int EVENT_ADD_NODES
Constant for the add nodes event.

EVENT_CLEAR_TREE

public static final int EVENT_CLEAR_TREE
Constant for the clear tree event.

root

private HierarchicalConfiguration.Node root
Stores the root node of this configuration. This field is required for backwards compatibility only.

rootNode

private ConfigurationNode rootNode
Stores the root configuration node.

serialVersionUID

private static final long serialVersionUID
The serial version UID.

Constructor Detail

HierarchicalConfiguration

public HierarchicalConfiguration()
Creates a new instance of HierarchicalConfiguration.

HierarchicalConfiguration

public HierarchicalConfiguration(HierarchicalConfiguration c)
Creates a new instance of HierarchicalConfiguration and copies all data contained in the specified configuration into the new one.

Parameters: c the configuration that is to be copied (if null, this constructor will behave like the standard constructor)

Since: 1.4

Method Detail

addNodes

public void addNodes(String key, Collection nodes)
Adds a collection of nodes at the specified position of the configuration tree. This method works similar to addProperty(), but instead of a single property a whole collection of nodes can be added - and thus complete configuration sub trees. E.g. with this method it is possible to add parts of another HierarchicalConfiguration object to this object. If the passed in key refers to an existing and unique node, the new nodes are added to this node. Otherwise a new node will be created at the specified position in the hierarchy.

Parameters: key the key where the nodes are to be added; can be null , then they are added to the root node nodes a collection with the Node objects to be added

addPropertyDirect

protected void addPropertyDirect(String key, Object obj)
Adds the property with the specified key. This task will be delegated to the associated ExpressionEngine, so the passed in key must match the requirements of this implementation.

Parameters: key the key of the new property obj the value of the new property

clearNode

protected void clearNode(HierarchicalConfiguration.Node node)

Deprecated: Use the method clearNode instead

Clears the value of the specified node. If the node becomes undefined by this operation, it is removed from the hierarchy.

Parameters: node the node to be cleard

clearNode

protected void clearNode(ConfigurationNode node)
Clears the value of the specified node. If the node becomes undefined by this operation, it is removed from the hierarchy.

Parameters: node the node to be cleard

clearProperty

public void clearProperty(String key)
Removes the property with the given key. Properties with names that start with the given key (i.e. properties below the specified key in the hierarchy) won't be affected.

Parameters: key the key of the property to be removed

clearReferences

protected static void clearReferences(ConfigurationNode node)
Clears all reference fields in a node structure. A configuration node can store a so-called "reference". The meaning of this data is determined by a concrete sub class. Typically such references are specific for a configuration instance. If this instance is cloned or copied, they must be cleared. This can be done using this method.

Parameters: node the root node of the node hierarchy, in which the references are to be cleared

Since: 1.4

clearTree

public void clearTree(String key)
Removes all values of the property with the given name and of keys that start with this name. So if there is a property with the key "foo" and a property with the key "foo.bar", a call of clearTree("foo") would remove both properties.

Parameters: key the key of the property to be removed

clone

public Object clone()
Creates a copy of this object. This new configuration object will contain copies of all nodes in the same structure. Registered event listeners won't be cloned; so they are not registered at the returned copy.

Returns: the copy

Since: 1.2

configurationAt

public SubnodeConfiguration configurationAt(String key)

Returns a hierarchical subnode configuration object that wraps the configuration node specified by the given key. This method provides an easy means of accessing sub trees of a hierarchical configuration. In the returned configuration the sub tree can directly be accessed, it becomes the root node of this configuration. Because of this the passed in key must select exactly one configuration node; otherwise an IllegalArgumentException will be thrown.

The difference between this method and the subset method is that subset() supports arbitrary subsets of configuration nodes while configurationAt() only returns a single sub tree. Please refer to the documentation of the SubnodeConfiguration class to obtain further information about subnode configurations and when they should be used.

Parameters: key the key that selects the sub tree

Returns: a hierarchical configuration that contains this sub tree

Since: 1.3

See Also: SubnodeConfiguration

configurationsAt

public List configurationsAt(String key)
Returns a list of sub configurations for all configuration nodes selected by the given key. This method will evaluate the passed in key (using the current ExpressionEngine) and then create a subnode configuration for each returned node (like configurationAt}). This is especially useful when dealing with list-like structures. As an example consider the configuration that contains data about database tables and their fields. If you need access to all fields of a certain table, you can simply do
 List fields = config.configurationsAt("tables.table(0).fields.field");
 for(Iterator it = fields.iterator(); it.hasNext();)
 {
     HierarchicalConfiguration sub = (HierarchicalConfiguration) it.next();
     // now the children and attributes of the field node can be
     // directly accessed
     String fieldName = sub.getString("name");
     String fieldType = sub.getString("type");
     ...
 

Parameters: key the key for selecting the desired nodes

Returns: a list with hierarchical configuration objects; each configuration represents one of the nodes selected by the passed in key

Since: 1.3

containsKey

public boolean containsKey(String key)
Checks if the specified key is contained in this configuration. Note that for this configuration the term "contained" means that the key has an associated value. If there is a node for this key that has no value but children (either defined or undefined), this method will still return false .

Parameters: key the key to be chekced

Returns: a flag if this key is contained in this configuration

createAddPath

protected HierarchicalConfiguration.Node createAddPath(ConfigurationKey.KeyIterator keyIt, HierarchicalConfiguration.Node root)

Deprecated: Adding new properties is now to a major part delegated to the ExpressionEngine associated with this configuration instance. This method will no longer be called. Developers who want to modify the process of adding new properties should consider implementing their own expression engine.

Creates the missing nodes for adding a new property. This method ensures that there are corresponding nodes for all components of the specified configuration key.

Parameters: keyIt the key iterator root the base node of the path to be created

Returns: the last node of the path

createNode

protected HierarchicalConfiguration.Node createNode(String name)
Creates a new Node object with the specified name. This method can be overloaded in derived classes if a specific node type is needed. This base implementation always returns a new object of the Node class.

Parameters: name the name of the new node

Returns: the new node

createSubnodeConfiguration

protected SubnodeConfiguration createSubnodeConfiguration(ConfigurationNode node)
Creates a subnode configuration for the specified node. This method is called by configurationAt() and configurationsAt().

Parameters: node the node, for which a subnode configuration is to be created

Returns: the configuration for the given node

Since: 1.3

fetchAddNode

protected HierarchicalConfiguration.Node fetchAddNode(ConfigurationKey.KeyIterator keyIt, HierarchicalConfiguration.Node startNode)

Deprecated: Adding new properties is now to a major part delegated to the ExpressionEngine associated with this configuration instance. This method will no longer be called. Developers who want to modify the process of adding new properties should consider implementing their own expression engine.

Returns a reference to the parent node of an add operation. Nodes for new properties can be added as children of this node. If the path for the specified key does not exist so far, it is created now.

Parameters: keyIt the iterator for the key of the new property startNode the node to start the search with

Returns: the parent node for the add operation

fetchNodeList

protected List fetchNodeList(String key)
Helper method for fetching a list of all nodes that are addressed by the specified key.

Parameters: key the key

Returns: a list with all affected nodes (never null )

findLastPathNode

protected HierarchicalConfiguration.Node findLastPathNode(ConfigurationKey.KeyIterator keyIt, HierarchicalConfiguration.Node node)

Deprecated: Adding new properties is now to a major part delegated to the ExpressionEngine associated with this configuration instance. This method will no longer be called. Developers who want to modify the process of adding new properties should consider implementing their own expression engine.

Finds the last existing node for an add operation. This method traverses the configuration tree along the specified key. The last existing node on this path is returned.

Parameters: keyIt the key iterator node the actual node

Returns: the last existing node on the given path

findPropertyNodes

protected void findPropertyNodes(ConfigurationKey.KeyIterator keyPart, HierarchicalConfiguration.Node node, Collection nodes)

Deprecated: Property keys are now evaluated by the expression engine associated with the configuration; this method will no longer be called. If you want to modify the way properties are looked up, consider implementing you own ExpressionEngine implementation.

Recursive helper method for fetching a property. This method processes all facets of a configuration key, traverses the tree of properties and fetches the the nodes of all matching properties.

Parameters: keyPart the configuration key iterator node the actual node nodes here the found nodes are stored

getDefaultExpressionEngine

public static ExpressionEngine getDefaultExpressionEngine()
Returns the default expression engine.

Returns: the default expression engine

Since: 1.3

getExpressionEngine

public ExpressionEngine getExpressionEngine()
Returns the expression engine used by this configuration. This method will never return null; if no specific expression engine was set, the default expression engine will be returned.

Returns: the current expression engine

Since: 1.3

getKeys

public Iterator getKeys()
Returns an iterator with all keys defined in this configuration. Note that the keys returned by this method will not contain any indices. This means that some structure will be lost.

Returns: an iterator with the defined keys in this configuration

getKeys

public Iterator getKeys(String prefix)
Returns an iterator with all keys defined in this configuration that start with the given prefix. The returned keys will not contain any indices.

Parameters: prefix the prefix of the keys to start with

Returns: an iterator with the found keys

getMaxIndex

public int getMaxIndex(String key)
Returns the maximum defined index for the given key. This is useful if there are multiple values for this key. They can then be addressed separately by specifying indices from 0 to the return value of this method.

Parameters: key the key to be checked

Returns: the maximum defined index for this key

getProperty

public Object getProperty(String key)
Fetches the specified property. This task is delegated to the associated expression engine.

Parameters: key the key to be looked up

Returns: the found value

getRoot

public HierarchicalConfiguration.Node getRoot()
Returns the root node of this hierarchical configuration. This method exists for backwards compatibility only. New code should use the getRootNode method instead, which operates on the preferred data type ConfigurationNode.

Returns: the root node

getRootNode

public ConfigurationNode getRootNode()
Returns the root node of this hierarchical configuration.

Returns: the root node

Since: 1.3

isEmpty

public boolean isEmpty()
Checks if this configuration is empty. Empty means that there are no keys with any values, though there can be some (empty) nodes.

Returns: a flag if this configuration is empty

nodeDefined

protected boolean nodeDefined(HierarchicalConfiguration.Node node)

Deprecated: Use the method nodeDefined instead.

Checks if the specified node is defined.

Parameters: node the node to be checked

Returns: a flag if this node is defined

nodeDefined

protected boolean nodeDefined(ConfigurationNode node)
Checks if the specified node is defined.

Parameters: node the node to be checked

Returns: a flag if this node is defined

processNodeAddData

private ConfigurationNode processNodeAddData(NodeAddData data)
Helper method for processing a node add data object obtained from the expression engine. This method will create all new nodes.

Parameters: data the data object

Returns: the new node

Since: 1.3

removeNode

protected void removeNode(HierarchicalConfiguration.Node node)

Deprecated: Use the method removeNode instead.

Removes the specified node from this configuration. This method ensures that parent nodes that become undefined by this operation are also removed.

Parameters: node the node to be removed

removeNode

protected void removeNode(ConfigurationNode node)
Removes the specified node from this configuration. This method ensures that parent nodes that become undefined by this operation are also removed.

Parameters: node the node to be removed

setDefaultExpressionEngine

public static void setDefaultExpressionEngine(ExpressionEngine engine)
Sets the default expression engine. This expression engine will be used if no specific engine was set for an instance. It is shared between all hierarchical configuration instances. So modifying its properties will impact all instances, for which no specific engine is set.

Parameters: engine the new default expression engine

Since: 1.3

setExpressionEngine

public void setExpressionEngine(ExpressionEngine expressionEngine)
Sets the expression engine to be used by this configuration. All property keys this configuration has to deal with will be interpreted by this engine.

Parameters: expressionEngine the new expression engine; can be null, then the default expression engine will be used

Since: 1.3

setProperty

public void setProperty(String key, Object value)
Sets the value of the specified property.

Parameters: key the key of the property to set value the new value of this property

setRoot

public void setRoot(HierarchicalConfiguration.Node node)
Sets the root node of this hierarchical configuration. This method exists for backwards compatibility only. New code should use the setRootNode method instead, which operates on the preferred data type ConfigurationNode.

Parameters: node the root node

setRootNode

public void setRootNode(ConfigurationNode rootNode)
Sets the root node of this hierarchical configuration.

Parameters: rootNode the root node

Since: 1.3

subset

public Configuration subset(String prefix)
Creates a new Configuration object containing all keys that start with the specified prefix. This implementation will return a HierarchicalConfiguration object so that the structure of the keys will be saved.

Parameters: prefix the prefix of the keys for the subset

Returns: a new configuration object representing the selected subset