org.apache.commons.configuration.tree
Interface ExpressionEngine

All Known Implementing Classes:

DefaultExpressionEngine, XPathExpressionEngine

public interface ExpressionEngine

Definition of an interface for evaluating keys for hierarchical configurations.

An expression engine knows how to map a key for a configuration's property to a single or a set of configuration nodes. Thus it defines the way how properties are addressed in this configuration. Methods of a configuration that have to handle property key (e.g. getProperty() or addProperty() do not interpret the passed in keys on their own, but delegate this task to an associated expression engine. This expression engine will then find out, which configuration nodes are addressed by the key.

Seperating the task of evaluating property keys from the configuration object has the advantage that many different expression languages (i.e. ways for querying or setting properties) can be supported. Just set a suitable implementation of this interface as the configuration's expression engine, and you can use the syntax provided by this implementation.

Since:

1.3

Author:

Oliver Heger

Method Summary

String	nodeKey(ConfigurationNode node, String parentKey) Returns the key for the specified node in the expression language supported by an implementation.
NodeAddData	prepareAdd(ConfigurationNode root, String key) Returns information needed for an add operation.
List	query(ConfigurationNode root, String key) Finds the node(s) that is (are) matched by the specified key.

Method Detail

query

List query(ConfigurationNode root,
           String key)

Finds the node(s) that is (are) matched by the specified key. This is the main method for interpreting property keys. An implementation must traverse the given root node and its children to find all nodes that are matched by the given key. If the key is not correct in the syntax provided by that implementation, it is free to throw a (runtime) exception indicating this error condition.

Parameters:

root - the root node of a hierarchy of configuration nodes

key - the key to be evaluated

Returns:

a list with the nodes that are matched by the key (should never be null)

nodeKey

String nodeKey(ConfigurationNode node,
               String parentKey)

Returns the key for the specified node in the expression language supported by an implementation. This method is called whenever a property key for a node has to be constructed, e.g. by the getKeys() method.

Parameters:

node - the node, for which the key must be constructed

parentKey - the key of this node's parent (can be null for the root node)

Returns:

this node's key

prepareAdd

NodeAddData prepareAdd(ConfigurationNode root,
                       String key)

Returns information needed for an add operation. This method gets called when new properties are to be added to a configuration. An implementation has to interpret the specified key, find the parent node for the new elements, and provide all information about new nodes to be added.

Parameters:

root - the root node

key - the key for the new property

Returns:

an object with all information needed for the add operation