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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 * @author Erwin Bolwidt (ejb @ klomp.org)
86 * @author J\u00e9r\u00f4me N\u00e8gre (jerome.negre @ e-xmlmedia.fr)
87 *
88 * @see <a href="http://www.w3.org/TR/xpath#function-id" target="_top">Section 4.1 of the XPath Specification</a>
89 */
90 public class IdFunction implements Function
91 {
92
93 /***
94 * Create a new <code>IdFunction</code> object.
95 */
96 public IdFunction() {}
97
98 /***
99 * Returns the node with the specified ID.
100 *
101 * @param context the context at the point in the
102 * expression when the function is called
103 * @param args a list with exactly one item which is either a string
104 * a node-set
105 *
106 * @return a <code>List</code> containing the node with the specified ID; or
107 * an empty list if there is no such node
108 *
109 * @throws FunctionCallException if <code>args</code> has more or less than one item
110 */
111 public Object call(Context context, List args) throws FunctionCallException
112 {
113 if ( args.size() == 1 ) {
114 return evaluate( context.getNodeSet(),
115 args.get(0), context.getNavigator() );
116 }
117
118 throw new FunctionCallException( "id() requires one argument" );
119 }
120
121 /***
122 * Returns the node with the specified ID.
123 * @param contextNodes the context node-set. The first item in this list
124 * determines the document in which the search is performed.
125 * @param arg the ID or IDs to search for
126 * @param nav the navigator used to calculate string-values and search
127 * by ID
128 *
129 * @return a <code>List</code> containing the node with the specified ID; or
130 * an empty list if there is no such node
131 *
132 */
133 public static List evaluate(List contextNodes, Object arg, Navigator nav)
134 {
135 if (contextNodes.size() == 0) return Collections.EMPTY_LIST;
136
137 List nodes = new ArrayList();
138
139 Object contextNode = contextNodes.get(0);
140
141 if (arg instanceof List) {
142 Iterator iter = ((List)arg).iterator();
143 while (iter.hasNext()) {
144 String id = StringFunction.evaluate(iter.next(), nav);
145 nodes.addAll( evaluate( contextNodes, id, nav ) );
146 }
147 }
148 else {
149 String ids = StringFunction.evaluate(arg, nav);
150 StringTokenizer tok = new StringTokenizer(ids, " \t\n\r");
151 while (tok.hasMoreTokens()) {
152 String id = tok.nextToken();
153 Object node = nav.getElementById(contextNode, id);
154 if (node != null) {
155 nodes.add(node);
156 }
157 }
158 }
159 return nodes;
160 }
161
162 }
163