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48 package org.jaxen.function;
49
50 import java.util.ArrayList;
51 import java.util.Collections;
52 import java.util.Iterator;
53 import java.util.List;
54 import java.util.StringTokenizer;
55
56 import org.jaxen.Context;
57 import org.jaxen.Function;
58 import org.jaxen.FunctionCallException;
59 import org.jaxen.Navigator;
60
61 /***
62 * <p><b>4.1</b> <code><i>node-set</i> id(<i>object</i>)</code> </p>
63 *
64 * <p>The <b>id</b> function returns a <code>List</code>
65 * of all the elements in the context document that have an ID
66 * matching one of a specified list of IDs. How an attribute is determined
67 * to be of type ID depends on the navigator, but it normally requires that
68 * the attribute be declared to have type ID in the DTD.
69 * </p>
70 *
71 * <p>
72 * There should be no more than one element in any document with a
73 * certain ID. However, if there are multiple such elements--i.e. if
74 * there are duplicate IDs--then this function selects only the first element
75 * in document order with the specified ID.
76 * </p>
77 *
78 * @author Erwin Bolwidt (ejb @ klomp.org)
79 * @author J\u00e9r\u00f4me N\u00e8gre (jerome.negre @ e-xmlmedia.fr)
80 *
81 * @see <a href="http://www.w3.org/TR/xpath#function-id" target="_top">Section 4.1 of the XPath Specification</a>
82 */
83 public class IdFunction implements Function
84 {
85
86 /***
87 * Create a new <code>IdFunction</code> object.
88 */
89 public IdFunction() {}
90
91 /***
92 * Returns a list of the nodes with the specified IDs.
93 *
94 * @param context the context at the point in the
95 * expression when the function is called
96 * @param args a list with exactly one item which is either a string
97 * a node-set
98 *
99 * @return a <code>List</code> containing the first node in document
100 * with each of the specified IDs; or
101 * an empty list if there are no such nodes
102 *
103 * @throws FunctionCallException if <code>args</code> has more or less than one item
104 */
105 public Object call(Context context, List args) throws FunctionCallException
106 {
107 if ( args.size() == 1 ) {
108 return evaluate( context.getNodeSet(),
109 args.get(0), context.getNavigator() );
110 }
111
112 throw new FunctionCallException( "id() requires one argument" );
113 }
114
115 /***
116 * Returns a list of the nodes with the specified IDs.
117 *
118 * @param contextNodes the context node-set. The first item in this list
119 * determines the document in which the search is performed.
120 * @param arg the ID or IDs to search for
121 * @param nav the navigator used to calculate string-values and search
122 * by ID
123 *
124 * @return a <code>List</code> containing the first node in document
125 * with each of the specified IDs; or
126 * an empty list if there are no such nodes
127 *
128 */
129 public static List evaluate(List contextNodes, Object arg, Navigator nav)
130 {
131 if (contextNodes.size() == 0) return Collections.EMPTY_LIST;
132
133 List nodes = new ArrayList();
134
135 Object contextNode = contextNodes.get(0);
136
137 if (arg instanceof List) {
138 Iterator iter = ((List)arg).iterator();
139 while (iter.hasNext()) {
140 String id = StringFunction.evaluate(iter.next(), nav);
141 nodes.addAll( evaluate( contextNodes, id, nav ) );
142 }
143 }
144 else {
145 String ids = StringFunction.evaluate(arg, nav);
146 StringTokenizer tok = new StringTokenizer(ids, " \t\n\r");
147 while (tok.hasMoreTokens()) {
148 String id = tok.nextToken();
149 Object node = nav.getElementById(contextNode, id);
150 if (node != null) {
151 nodes.add(node);
152 }
153 }
154 }
155 return nodes;
156 }
157
158 }
159