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62 package org.jaxen.function;
63
64 import java.util.ArrayList;
65 import java.util.Collections;
66 import java.util.Iterator;
67 import java.util.List;
68 import java.util.StringTokenizer;
69
70 import org.jaxen.Context;
71 import org.jaxen.Function;
72 import org.jaxen.FunctionCallException;
73 import org.jaxen.Navigator;
74
75 /***
76 * <p><b>4.1</b> <code><i>node-set</i> id(<i>object</i>)</code> </p>
77 *
78 * <p>The <b>id</b> function returns a <code>List</code>
79 * of all the elements in the context document that have an ID
80 * matching one of a specified list of IDs. How an attribute is determined
81 * to be of type ID depends on the navigator, but it normally requires that
82 * the attribute be declared to have type ID in the DTD.
83 * </p>
84 *
85 * <p>
86 * There should be no more than one element in any document with a
87 * certain ID. However, if there are multiple such elements--i.e. if
88 * there are duplicate IDs--then this function selects only the first element
89 * in document order with the specified ID.
90 * </p>
91 *
92 * @author Erwin Bolwidt (ejb @ klomp.org)
93 * @author J\u00e9r\u00f4me N\u00e8gre (jerome.negre @ e-xmlmedia.fr)
94 *
95 * @see <a href="http://www.w3.org/TR/xpath#function-id" target="_top">Section 4.1 of the XPath Specification</a>
96 */
97 public class IdFunction implements Function
98 {
99
100 /***
101 * Create a new <code>IdFunction</code> object.
102 */
103 public IdFunction() {}
104
105 /***
106 * Returns a list of the nodes with the specified IDs.
107 *
108 * @param context the context at the point in the
109 * expression when the function is called
110 * @param args a list with exactly one item which is either a string
111 * a node-set
112 *
113 * @return a <code>List</code> containing the first node in document
114 * with each of the specified IDs; or
115 * an empty list if there are no such nodes
116 *
117 * @throws FunctionCallException if <code>args</code> has more or less than one item
118 */
119 public Object call(Context context, List args) throws FunctionCallException
120 {
121 if ( args.size() == 1 ) {
122 return evaluate( context.getNodeSet(),
123 args.get(0), context.getNavigator() );
124 }
125
126 throw new FunctionCallException( "id() requires one argument" );
127 }
128
129 /***
130 * Returns a list of the nodes with the specified IDs.
131 *
132 * @param contextNodes the context node-set. The first item in this list
133 * determines the document in which the search is performed.
134 * @param arg the ID or IDs to search for
135 * @param nav the navigator used to calculate string-values and search
136 * by ID
137 *
138 * @return a <code>List</code> containing the first node in document
139 * with each of the specified IDs; or
140 * an empty list if there are no such nodes
141 *
142 */
143 public static List evaluate(List contextNodes, Object arg, Navigator nav)
144 {
145 if (contextNodes.size() == 0) return Collections.EMPTY_LIST;
146
147 List nodes = new ArrayList();
148
149 Object contextNode = contextNodes.get(0);
150
151 if (arg instanceof List) {
152 Iterator iter = ((List)arg).iterator();
153 while (iter.hasNext()) {
154 String id = StringFunction.evaluate(iter.next(), nav);
155 nodes.addAll( evaluate( contextNodes, id, nav ) );
156 }
157 }
158 else {
159 String ids = StringFunction.evaluate(arg, nav);
160 StringTokenizer tok = new StringTokenizer(ids, " \t\n\r");
161 while (tok.hasMoreTokens()) {
162 String id = tok.nextToken();
163 Object node = nav.getElementById(contextNode, id);
164 if (node != null) {
165 nodes.add(node);
166 }
167 }
168 }
169 return nodes;
170 }
171
172 }
173