org.apache.commons.configuration
Class HierarchicalConfiguration

java.lang.Object
  org.apache.commons.configuration.AbstractConfiguration
      org.apache.commons.configuration.HierarchicalConfiguration

All Implemented Interfaces:

Configuration

Direct Known Subclasses:

HierarchicalXMLConfiguration

public class HierarchicalConfiguration

extends AbstractConfiguration

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 1.11 2004/10/11 09:27:20 henning Exp $

Author:

Oliver Heger

Nested Class Summary

(package private) static class	HierarchicalConfiguration.CloneVisitor A specialized visitor that is able to create a deep copy of a node hierarchy.
(package private) static class	HierarchicalConfiguration.DefinedKeysVisitor A specialized visitor that fills a list with keys that are defined in a node hierarchy.
(package private) static class	HierarchicalConfiguration.DefinedVisitor A specialized visitor that checks if a node is defined.
static class	HierarchicalConfiguration.Node A data class for storing (hierarchical) property information.
static class	HierarchicalConfiguration.NodeVisitor Definition of a visitor class for traversing a node and all of its children.

Nested classes inherited from class org.apache.commons.configuration.AbstractConfiguration

AbstractConfiguration.PropertiesTokenizer

Field Summary

Fields inherited from class org.apache.commons.configuration.AbstractConfiguration

END_TOKEN, START_TOKEN

Constructor Summary

HierarchicalConfiguration()
Creates a new instance of HierarchicalConfiguration.

Method Summary

void	addNodes(String key, Collection nodes) Adds a collection of nodes at the specified position of the configuration tree.
protected void	addPropertyDirect(String key, Object obj) Adds the property with the specified key.
void	clearProperty(String key) Removes all values of the property with the given name.
boolean	containsKey(String key) Checks if the specified key is contained in this configuration.
protected HierarchicalConfiguration.Node	createAddPath(ConfigurationKey.KeyIterator keyIt, HierarchicalConfiguration.Node root) Creates the missing nodes for adding a new property.
protected HierarchicalConfiguration.Node	fetchAddNode(ConfigurationKey.KeyIterator keyIt, HierarchicalConfiguration.Node startNode) Returns a reference to the parent node of an add operation.
protected List	fetchNodeList(String key) Helper method for fetching a list of all nodes that are addressed by the specified key.
protected HierarchicalConfiguration.Node	findLastPathNode(ConfigurationKey.KeyIterator keyIt, HierarchicalConfiguration.Node node) Finds the last existing node for an add operation.
protected void	findPropertyNodes(ConfigurationKey.KeyIterator keyPart, HierarchicalConfiguration.Node node, Collection data) Recursive helper method for fetching a property.
Iterator	getKeys() Returns an iterator with all keys defined in this configuration.
int	getMaxIndex(String key) Returns the maximum defined index for the given key.
protected Object	getPropertyDirect(String key) Fetches the specified property.
HierarchicalConfiguration.Node	getRoot() Returns the root node of this hierarchical configuration.
boolean	isEmpty() Checks if this configuration is empty.
protected boolean	nodeDefined(HierarchicalConfiguration.Node node) Checks if the specified node is defined.
protected void	removeNode(HierarchicalConfiguration.Node node) Removes the specified node from this configuration.
void	setRoot(HierarchicalConfiguration.Node node) Sets the root node of this hierarchical configuration.
Configuration	subset(String prefix) Creates a new Configuration object containing all keys that start with the specified prefix.

Methods inherited from class org.apache.commons.configuration.AbstractConfiguration

addProperty, getBigDecimal, getBigDecimal, getBigInteger, getBigInteger, getBoolean, getBoolean, getBoolean, getByte, getByte, getByte, getDelimiter, getDouble, getDouble, getDouble, getFloat, getFloat, getFloat, getInt, getInt, getInteger, getKeys, getList, getList, getLong, getLong, getLong, getProperties, getProperties, getProperty, getShort, getShort, getShort, getString, getString, getStringArray, getVector, getVector, interpolate, interpolateHelper, isThrowExceptionOnMissing, setDelimiter, setProperty, setThrowExceptionOnMissing, split

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

HierarchicalConfiguration

public HierarchicalConfiguration()

Creates a new instance of HierarchicalConfiguration.

Method Detail

getRoot

public HierarchicalConfiguration.Node getRoot()

Returns the root node of this hierarchical configuration.

Returns:

the root node

setRoot

public void setRoot(HierarchicalConfiguration.Node node)

Sets the root node of this hierarchical configuration.

Parameters:

node - the root node

getPropertyDirect

protected Object getPropertyDirect(String key)

Fetches the specified property. Performs a recursive lookup in the tree with the configuration properties.

Specified by:

getPropertyDirect in class AbstractConfiguration

Parameters:

key - the key to be looked up

Returns:

the found value

addPropertyDirect

protected void addPropertyDirect(String key,
                                 Object obj)

Adds the property with the specified key.

To be able to deal with the structure supported by this configuration implementation the passed in key is of importance, especially the indices it might contain. The following example should clearify this: Suppose the actual configuration contains the following elements:

 tables
    +-- table
            +-- name = user
            +-- fields
                    +-- field
                            +-- name = uid
                    +-- field
                            +-- name = firstName
                    ...
    +-- table
            +-- name = documents
            +-- fields
                   ...
 

In this example a database structure is defined, e.g. all fields of the first table could be accessed using the key tables.table(0).fields.field.name. If now properties are to be added, it must be exactly specified at which position in the hierarchy the new property is to be inserted. So to add a new field name to a table it is not enough to say just

 config.addProperty("tables.table.fields.field.name", "newField");
 

The statement given above contains some ambiguity. For instance it is not clear, to which table the new field should be added. If this method finds such an ambiguity, it is resolved by following the last valid path. Here this would be the last table. The same is true for the field; because there are multiple fields and no explicit index is provided, a new name property would be added to the last field - which is propably not what was desired.

To make things clear explicit indices should be provided whenever possible. In the example above the exact table could be specified by providing an index for the table element as in tables.table(1).fields. By specifying an index it can also be expressed that at a given position in the configuration tree a new branch should be added. In the example above we did not want to add an additional name element to the last field of the table, but we want a complete new field element. This can be achieved by specifying an invalid index (like -1) after the element where a new branch should be created. Given this our example would run:

 config.addProperty("tables.table(1).fields.field(-1).name", "newField");
 

With this notation it is possible to add new branches everywhere. We could for instance create a new table element by specifying

 config.addProperty("tables.table(-1).fields.field.name", "newField2");
 

(Note that because after the table element a new branch is created indices in following elements are not relevant; the branch is new so there cannot be any ambiguities.)

Specified by:

addPropertyDirect in class AbstractConfiguration

Parameters:

key - the key of the new property

obj - the value of the new property

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.

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

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.

Specified by:

isEmpty in interface Configuration

Specified by:

isEmpty in class AbstractConfiguration

Returns:

a flag if this configuration is empty

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.

Specified by:

subset in interface Configuration

Overrides:

subset in class AbstractConfiguration

Parameters:

prefix - the prefix of the keys for the subset

Returns:

a new configuration object representing the selected subset

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.

Specified by:

containsKey in interface Configuration

Specified by:

containsKey in class AbstractConfiguration

Parameters:

key - the key to be chekced

Returns:

a flag if this key is contained in this configuration

clearProperty

public void clearProperty(String key)

Removes all values of the property with the given name.

Specified by:

clearProperty in interface Configuration

Specified by:

clearProperty in class AbstractConfiguration

Parameters:

key - the key of the property to be removed

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.

Specified by:

getKeys in interface Configuration

Specified by:

getKeys in class AbstractConfiguration

Returns:

an iterator with the defined keys in this configuration

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

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)

findPropertyNodes

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

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

data - here the found nodes are stored

nodeDefined

protected boolean nodeDefined(HierarchicalConfiguration.Node node)

Checks if the specified node is defined.

Parameters:

node - the node to be checked

Returns:

a flag if this node is defined

removeNode

protected void removeNode(HierarchicalConfiguration.Node 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

fetchAddNode

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

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

findLastPathNode

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

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

createAddPath

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

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