01: /*
02: * Licensed to the Apache Software Foundation (ASF) under one or more
03: * contributor license agreements. See the NOTICE file distributed with
04: * this work for additional information regarding copyright ownership.
05: * The ASF licenses this file to You under the Apache License, Version 2.0
06: * (the "License"); you may not use this file except in compliance with
07: * the License. You may obtain a copy of the License at
08: *
09: * http://www.apache.org/licenses/LICENSE-2.0
10: *
11: * Unless required by applicable law or agreed to in writing, software
12: * distributed under the License is distributed on an "AS IS" BASIS,
13: * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14: * See the License for the specific language governing permissions and
15: * limitations under the License.
16: */
17: package org.apache.commons.configuration.tree;
18:
19: import java.util.List;
20:
21: /**
22: * <p>
23: * Definition of an interface for evaluating keys for hierarchical
24: * configurations.
25: * </p>
26: * <p>
27: * An <em>expression engine</em> knows how to map a key for a configuration's
28: * property to a single or a set of configuration nodes. Thus it defines the way
29: * how properties are addressed in this configuration. Methods of a
30: * configuration that have to handle property key (e.g.
31: * <code>getProperty()</code> or <code>addProperty()</code> do not interpret
32: * the passed in keys on their own, but delegate this task to an associated
33: * expression engine. This expression engine will then find out, which
34: * configuration nodes are addressed by the key.
35: * </p>
36: * <p>
37: * Seperating the task of evaluating property keys from the configuration object
38: * has the advantage that many different expression languages (i.e. ways for
39: * querying or setting properties) can be supported. Just set a suitable
40: * implementation of this interface as the configuration's expression engine,
41: * and you can use the syntax provided by this implementation.
42: * </p>
43: *
44: * @since 1.3
45: * @author Oliver Heger
46: */
47: public interface ExpressionEngine {
48: /**
49: * Finds the node(s) that is (are) matched by the specified key. This is the
50: * main method for interpreting property keys. An implementation must
51: * traverse the given root node and its children to find all nodes that are
52: * matched by the given key. If the key is not correct in the syntax
53: * provided by that implementation, it is free to throw a (runtime)
54: * exception indicating this error condition.
55: *
56: * @param root the root node of a hierarchy of configuration nodes
57: * @param key the key to be evaluated
58: * @return a list with the nodes that are matched by the key (should never
59: * be <b>null</b>)
60: */
61: List query(ConfigurationNode root, String key);
62:
63: /**
64: * Returns the key for the specified node in the expression language
65: * supported by an implementation. This method is called whenever a property
66: * key for a node has to be constructed, e.g. by the
67: * <code>{@link org.apache.commons.configuration.Configuration#getKeys() getKeys()}</code>
68: * method.
69: *
70: * @param node the node, for which the key must be constructed
71: * @param parentKey the key of this node's parent (can be <b>null</b> for
72: * the root node)
73: * @return this node's key
74: */
75: String nodeKey(ConfigurationNode node, String parentKey);
76:
77: /**
78: * Returns information needed for an add operation. This method gets called
79: * when new properties are to be added to a configuration. An implementation
80: * has to interpret the specified key, find the parent node for the new
81: * elements, and provide all information about new nodes to be added.
82: *
83: * @param root the root node
84: * @param key the key for the new property
85: * @return an object with all information needed for the add operation
86: */
87: NodeAddData prepareAdd(ConfigurationNode root, String key);
88: }
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