1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * 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.configuration2.tree;
18
19 import java.util.List;
20 import java.util.Set;
21
22 /**
23 * <p>
24 * Definition of an interface for accessing the data of a configuration node.
25 * </p>
26 * <p>
27 * Hierarchical configurations can deal with arbitrary node structures. In order to obtain information about a specific
28 * node object, a so-called {@code NodeHandler} is used. The handler provides a number of methods for querying the
29 * internal state of a node in a read-only way.
30 * </p>
31 *
32 * @param <T> the type of the nodes this handler deals with
33 */
34 public interface NodeHandler<T> {
35 /**
36 * Gets an unmodifiable set with the names of all attributes of the specified node.
37 *
38 * @param node the node
39 * @return a set with the names of all attributes of this node
40 */
41 Set<String> getAttributes(T node);
42
43 /**
44 * Gets the value of the specified attribute from the given node. If a concrete {@code NodeHandler} supports
45 * attributes with multiple values, result might be a collection.
46 *
47 * @param node the node
48 * @param name the name of the attribute
49 * @return the value of this attribute
50 */
51 Object getAttributeValue(T node, String name);
52
53 /**
54 * Gets the child with the given index of the specified node.
55 *
56 * @param node the node
57 * @param index the index (0-based)
58 * @return the child with the given index
59 */
60 T getChild(T node, int index);
61
62 /**
63 * Gets an unmodifiable list with all children of the specified node.
64 *
65 * @param node the node
66 * @return a list with the child nodes of this node
67 */
68 List<T> getChildren(T node);
69
70 /**
71 * Gets an unmodifiable list of all children of the specified node with the given name.
72 *
73 * @param node the node
74 * @param name the name of the desired child nodes
75 * @return a list with all children with the given name
76 */
77 List<T> getChildren(T node, String name);
78
79 /**
80 * Gets the number of children of the specified node with the given name. This method exists for performance reasons:
81 * for some node implementations it may be by far more efficient to count the children than to query a list of all
82 * children and determine its size. A concrete implementation can choose the most efficient way to determine the number
83 * of children. If a child name is passed in, only the children with this name are taken into account. If the name
84 * <b>null</b> is passed, the total number of children must be returned.
85 *
86 * @param node the node
87 * @param name the name of the children in question (can be <b>null</b> for all children)
88 * @return the number of the selected children
89 */
90 int getChildrenCount(T node, String name);
91
92 /**
93 * Gets an unmodifiable list of all children of the specified node which are matched by the passed in
94 * {@code NodeMatcher} against the provided criterion. This method allows for advanced queries on a node's children.
95 *
96 * @param node the node
97 * @param matcher the {@code NodeMatcher} defining filter criteria
98 * @param criterion the criterion to be matched against; this object is passed to the {@code NodeMatcher}
99 * @param <C> the type of the criterion
100 * @return a list with all children matched by the matcher
101 */
102 <C> List<T> getMatchingChildren(T node, NodeMatcher<C> matcher, C criterion);
103
104 /**
105 * Gets the number of children of the specified node which are matched by the given {@code NodeMatcher}. This is a
106 * more generic version of {@link #getChildrenCount(Object, String)}. It allows checking for arbitrary filter
107 * conditions.
108 *
109 * @param node the node
110 * @param matcher the {@code NodeMatcher}
111 * @param criterion the criterion to be passed to the {@code NodeMatcher}
112 * @param <C> the type of the criterion
113 * @return the number of matched children
114 */
115 <C> int getMatchingChildrenCount(T node, NodeMatcher<C> matcher, C criterion);
116
117 /**
118 * Gets the parent of the specified node.
119 *
120 * @param node the node
121 * @return the parent node
122 */
123 T getParent(T node);
124
125 /**
126 * Gets the root node of the underlying hierarchy.
127 *
128 * @return the current root node
129 */
130 T getRootNode();
131
132 /**
133 * Gets the value of the specified node.
134 *
135 * @param node the node
136 * @return the value of this node
137 */
138 Object getValue(T node);
139
140 /**
141 * Returns a flag whether the passed in node has any attributes.
142 *
143 * @param node the node
144 * @return a flag whether this node has any attributes
145 */
146 boolean hasAttributes(T node);
147
148 /**
149 * Returns the index of the given child node in the list of children of its parent. This method is the opposite
150 * operation of {@link #getChild(Object, int)}. This method returns 0 if the given node is the first child node with
151 * this name, 1 for the second child node and so on. If the node has no parent node or if it is an attribute, -1 is
152 * returned.
153 *
154 * @param parent the parent node
155 * @param child a child node whose index is to be retrieved
156 * @return the index of this child node
157 */
158 int indexOfChild(T parent, T child);
159
160 /**
161 * Checks whether the specified node is defined. Nodes are "defined" if they contain any data, e.g. a value,
162 * or attributes, or defined children.
163 *
164 * @param node the node to test
165 * @return a flag whether the passed in node is defined
166 */
167 boolean isDefined(T node);
168
169 /**
170 * Returns the name of the specified node
171 *
172 * @param node the node
173 * @return the name of this node
174 */
175 String nodeName(T node);
176 }