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* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* 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
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.configuration2.tree;
import java.util.List;
/**
*
* 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 keys (e.g. {@code getProperty()}
* or {@code 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.
*
*
* Separating the task of evaluating property keys from the configuration object
* has the advantage that multiple 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.
*
*
* An {@code ExpressionEngine} can deal with nodes of different types. To
* achieve this, a {@link NodeHandler} for the desired type must be passed to
* the methods.
*
*
* @since 1.3
*/
public interface ExpressionEngine
{
/**
* Finds the nodes and/or attributes that 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 results
* 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. The passed in
* {@code NodeHandler} can be used to gather the required information from
* the node object.
*
* @param the type of the node to be processed
* @param root the root node of a hierarchy of nodes
* @param key the key to be evaluated
* @param handler the {@code NodeHandler} for accessing the node
* @return a list with the results that are matched by the key (should never
* be null)
*/
List> query(T root, String key, NodeHandler handler);
/**
* 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
* {@link org.apache.commons.configuration2.Configuration#getKeys()
* getKeys()} method.
*
* @param the type of the node to be processed
* @param node the node, for which the key must be constructed
* @param parentKey the key of this node's parent (can be null for
* the root node)
* @param handler the {@code NodeHandler} for accessing the node
* @return this node's key
*/
String nodeKey(T node, String parentKey, NodeHandler handler);
/**
* Returns the key of an attribute. The passed in {@code parentKey} must
* reference the parent node of the attribute. A concrete implementation
* must concatenate this parent key with the attribute name to a valid key
* for this attribute.
*
* @param parentKey the key to the node owning this attribute
* @param attributeName the name of the attribute in question
* @return the resulting key referencing this attribute
*/
String attributeKey(String parentKey, String attributeName);
/**
* Determines a "canonical" key for the specified node in the
* expression language supported by this implementation. This means that
* always a unique key if generated pointing to this specific node. For most
* concrete implementations, this means that an index is added to the node
* name to ensure that there are no ambiguities with child nodes having the
* same names.
*
* @param the type of the node to be processed
* @param node the node, for which the key must be constructed
* @param parentKey the key of this node's parent (can be null for
* the root node)
* @param handler the {@code NodeHandler} for accessing the node
* @return the canonical key of this node
*/
String canonicalKey(T node, String parentKey, NodeHandler handler);
/**
* 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.
*
* @param the type of the node to be processed
* @param root the root node
* @param key the key for the new property
* @param handler the {@code NodeHandler} for accessing the node
* @return an object with all information needed for the add operation
*/
NodeAddData prepareAdd(T root, String key, NodeHandler handler);
}