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17 package org.apache.commons.configuration.tree;
18
19 import java.util.Iterator;
20
21 /***
22 * <p>
23 * A concrete combiner implementation that is able to construct an override
24 * combination.
25 * </p>
26 * <p>
27 * An <em>override combination</em> means that nodes in the first node
28 * structure take precedence over nodes in the second, or - in other words -
29 * nodes of the second structure are only added to the resulting structure if
30 * they do not occure in the first one. This is especially suitable for dealing
31 * with the properties of configurations that are defined in an
32 * <code>override</code> section of a configuration definition file (hence the
33 * name).
34 * </p>
35 * <p>
36 * This combiner will iterate over the second node hierarchy and find all nodes
37 * that are not contained in the first hierarchy; these are added to the result.
38 * If a node can be found in both structures, it is checked whether a
39 * combination (in a recursive way) can be constructed for the two, which will
40 * then be added. Per default, nodes are combined, which occur only once in both
41 * structures. This test is implemented in the <code>canCombine()</code>
42 * method.
43 * </p>
44 * <p>
45 * As is true for the <code>{@link UnionCombiner}</code>, for this combiner
46 * list nodes are important. The <code>addListNode()</code> can be called to
47 * declare certain nodes as list nodes. This has the effect that these nodes
48 * will never be combined.
49 * </p>
50 *
51 * @author <a
52 * href="http://jakarta.apache.org/commons/configuration/team-list.html">Commons
53 * Configuration team</a>
54 * @version $Id: OverrideCombiner.java 439648 2006-09-02 20:42:10Z oheger $
55 * @since 1.3
56 */
57 public class OverrideCombiner extends NodeCombiner
58 {
59 /***
60 * Constructs an override combination for the passed in node structures.
61 *
62 * @param node1 the first node
63 * @param node2 the second node
64 * @return the resulting combined node structure
65 */
66 public ConfigurationNode combine(ConfigurationNode node1,
67 ConfigurationNode node2)
68 {
69 ViewNode result = createViewNode();
70 result.setName(node1.getName());
71
72
73 for (Iterator it = node1.getChildren().iterator(); it.hasNext();)
74 {
75 ConfigurationNode child = (ConfigurationNode) it.next();
76 ConfigurationNode child2 = canCombine(node1, node2, child);
77 if (child2 != null)
78 {
79 result.addChild(combine(child, child2));
80 }
81 else
82 {
83 result.addChild(child);
84 }
85 }
86
87
88
89 for (Iterator it = node2.getChildren().iterator(); it.hasNext();)
90 {
91 ConfigurationNode child = (ConfigurationNode) it.next();
92 if (node1.getChildrenCount(child.getName()) < 1)
93 {
94 result.addChild(child);
95 }
96 }
97
98
99 addAttributes(result, node1, node2);
100 result.setValue((node1.getValue() != null) ? node1.getValue() : node2
101 .getValue());
102
103 return result;
104 }
105
106 /***
107 * Handles the attributes during a combination process. First all attributes
108 * of the first node will be added to the result. Then all attributes of the
109 * second node, which are not contained in the first node, will also be
110 * added.
111 *
112 * @param result the resulting node
113 * @param node1 the first node
114 * @param node2 the second node
115 */
116 protected void addAttributes(ViewNode result, ConfigurationNode node1,
117 ConfigurationNode node2)
118 {
119 result.appendAttributes(node1);
120 for (Iterator it = node2.getAttributes().iterator(); it.hasNext();)
121 {
122 ConfigurationNode attr = (ConfigurationNode) it.next();
123 if (node1.getAttributeCount(attr.getName()) == 0)
124 {
125 result.addAttribute(attr);
126 }
127 }
128 }
129
130 /***
131 * Tests if a child node of the second node can be combined with the given
132 * child node of the first node. If this is the case, the corresponding node
133 * will be returned, otherwise <b>null</b>. This implementation checks
134 * whether the child node occurs only once in both hierarchies and is no
135 * known list node.
136 *
137 * @param node1 the first node
138 * @param node2 the second node
139 * @param child the child node (of the first node)
140 * @return a child of the second node, with which a combination is possible
141 */
142 protected ConfigurationNode canCombine(ConfigurationNode node1,
143 ConfigurationNode node2, ConfigurationNode child)
144 {
145 if (node2.getChildrenCount(child.getName()) == 1
146 && node1.getChildrenCount(child.getName()) == 1
147 && !isListNode(child))
148 {
149 return (ConfigurationNode) node2.getChildren(child.getName())
150 .get(0);
151 }
152 else
153 {
154 return null;
155 }
156 }
157 }