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 * https://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 /**
37 * Gets an unmodifiable set with the names of all attributes of the specified node.
38 *
39 * @param node the node
40 * @return a set with the names of all attributes of this node
41 */
42 Set<String> getAttributes(T node);
43
44 /**
45 * Gets the value of the specified attribute from the given node. If a concrete {@code NodeHandler} supports
46 * attributes with multiple values, result might be a collection.
47 *
48 * @param node the node
49 * @param name the name of the attribute
50 * @return the value of this attribute
51 */
52 Object getAttributeValue(T node, String name);
53
54 /**
55 * Gets the child with the given index of the specified node.
56 *
57 * @param node the node
58 * @param index the index (0-based)
59 * @return the child with the given index
60 */
61 T getChild(T node, int index);
62
63 /**
64 * Gets an unmodifiable list with all children of the specified node.
65 *
66 * @param node the node
67 * @return a list with the child nodes of this node
68 */
69 List<T> getChildren(T node);
70
71 /**
72 * Gets an unmodifiable list of all children of the specified node with the given name.
73 *
74 * @param node the node
75 * @param name the name of the desired child nodes
76 * @return a list with all children with the given name
77 */
78 List<T> getChildren(T node, String name);
79
80 /**
81 * Gets the number of children of the specified node with the given name. This method exists for performance reasons:
82 * for some node implementations it may be by far more efficient to count the children than to query a list of all
83 * children and determine its size. A concrete implementation can choose the most efficient way to determine the number
84 * of children. If a child name is passed in, only the children with this name are taken into account. If the name
85 * <strong>null</strong> is passed, the total number of children must be returned.
86 *
87 * @param node the node
88 * @param name the name of the children in question (can be <strong>null</strong> for all children)
89 * @return the number of the selected children
90 */
91 int getChildrenCount(T node, String name);
92
93 /**
94 * Gets an unmodifiable list of all children of the specified node which are matched by the passed in
95 * {@code NodeMatcher} against the provided criterion. This method allows for advanced queries on a node's children.
96 *
97 * @param node the node
98 * @param matcher the {@code NodeMatcher} defining filter criteria
99 * @param criterion the criterion to be matched against; this object is passed to the {@code NodeMatcher}
100 * @param <C> the type of the criterion
101 * @return a list with all children matched by the matcher
102 */
103 <C> List<T> getMatchingChildren(T node, NodeMatcher<C> matcher, C criterion);
104
105 /**
106 * Gets the number of children of the specified node which are matched by the given {@code NodeMatcher}. This is a
107 * more generic version of {@link #getChildrenCount(Object, String)}. It allows checking for arbitrary filter
108 * conditions.
109 *
110 * @param node the node
111 * @param matcher the {@code NodeMatcher}
112 * @param criterion the criterion to be passed to the {@code NodeMatcher}
113 * @param <C> the type of the criterion
114 * @return the number of matched children
115 */
116 <C> int getMatchingChildrenCount(T node, NodeMatcher<C> matcher, C criterion);
117
118 /**
119 * Gets the parent of the specified node.
120 *
121 * @param node the node
122 * @return the parent node
123 */
124 T getParent(T node);
125
126 /**
127 * Gets the root node of the underlying hierarchy.
128 *
129 * @return the current root node
130 */
131 T getRootNode();
132
133 /**
134 * Gets the value of the specified node.
135 *
136 * @param node the node
137 * @return the value of this node
138 */
139 Object getValue(T node);
140
141 /**
142 * Returns a flag whether the passed in node has any attributes.
143 *
144 * @param node the node
145 * @return a flag whether this node has any attributes
146 */
147 boolean hasAttributes(T node);
148
149 /**
150 * Returns the index of the given child node in the list of children of its parent. This method is the opposite
151 * operation of {@link #getChild(Object, int)}. This method returns 0 if the given node is the first child node with
152 * 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
153 * returned.
154 *
155 * @param parent the parent node
156 * @param child a child node whose index is to be retrieved
157 * @return the index of this child node
158 */
159 int indexOfChild(T parent, T child);
160
161 /**
162 * Checks whether the specified node is defined. Nodes are "defined" if they contain any data, for example a value,
163 * or attributes, or defined children.
164 *
165 * @param node the node to test
166 * @return a flag whether the passed in node is defined
167 */
168 boolean isDefined(T node);
169
170 /**
171 * Returns the name of the specified node
172 *
173 * @param node the node
174 * @return the name of this node
175 */
176 String nodeName(T node);
177 }