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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 {
/**
* 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 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 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);
/**
* 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);
}