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    1   /*
    2    * $Header: /home/projects/jaxen/scm/jaxen/src/java/main/org/jaxen/function/StringLengthFunction.java,v 1.10 2005/06/28 13:44:45 elharo Exp $
    3    * $Revision: 1.10 $
    4    * $Date: 2005/06/28 13:44:45 $
    5    *
    6    * ====================================================================
    7    *
    8    * Copyright (C) 2000-2002 bob mcwhirter & James Strachan.
    9    * All rights reserved.
    10   *
    11   * Redistribution and use in source and binary forms, with or without
    12   * modification, are permitted provided that the following conditions
    13   * are met:
    14   *
    15   * 1. Redistributions of source code must retain the above copyright
    16   *    notice, this list of conditions, and the following disclaimer.
    17   *
    18   * 2. Redistributions in binary form must reproduce the above copyright
    19   *    notice, this list of conditions, and the disclaimer that follows
    20   *    these conditions in the documentation and/or other materials
    21   *    provided with the distribution.
    22   *
    23   * 3. The name "Jaxen" must not be used to endorse or promote products
    24   *    derived from this software without prior written permission.  For
    25   *    written permission, please contact license@jaxen.org.
    26   *
    27   * 4. Products derived from this software may not be called "Jaxen", nor
    28   *    may "Jaxen" appear in their name, without prior written permission
    29   *    from the Jaxen Project Management (pm@jaxen.org).
    30   *
    31   * In addition, we request (but do not require) that you include in the
    32   * end-user documentation provided with the redistribution and/or in the
    33   * software itself an acknowledgement equivalent to the following:
    34   *     "This product includes software developed by the
    35   *      Jaxen Project <http://www.jaxen.org/>."
    36   * Alternatively, the acknowledgment may be graphical using the logos
    37   * available at http://www.jaxen.org/
    38   *
    39   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
    40   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
    41   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
    42   * DISCLAIMED.  IN NO EVENT SHALL THE Jaxen AUTHORS OR THE PROJECT
    43   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
    44   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
    45   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
    46   * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
    47   * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
    48   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
    49   * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    50   * SUCH DAMAGE.
    51   *
    52   * ====================================================================
    53   * This software consists of voluntary contributions made by many
    54   * individuals on behalf of the Jaxen Project and was originally
    55   * created by bob mcwhirter <bob@werken.com> and
    56   * James Strachan <jstrachan@apache.org>.  For more information on the
    57   * Jaxen Project, please see <http://www.jaxen.org/>.
    58   *
    59   * $Id: StringLengthFunction.java,v 1.10 2005/06/28 13:44:45 elharo Exp $
    60   */
    61
    62
    63  package org.jaxen.function;
    64
    65  import java.util.List;
    66
    67  import org.jaxen.Context;
    68  import org.jaxen.Function;
    69  import org.jaxen.FunctionCallException;
    70  import org.jaxen.Navigator;
    71
    72  /***
    73   * <p><b>4.2</b> <code><i>number</i> string-length(<i>string</i>)</code></p>
    74   *
    75   * <p>
    76   * The <b>string-length</b> function returns the number of <strong>Unicode characters</strong>
    77   * in its argument. This is <strong>not</strong> necessarily
    78   * the same as the number <strong>Java chars</strong>
    79   * in the corresponding Java string. In particular, if the Java <code>String</code>
    80   * contains surrogate pairs each such pair will be counted as only one character
    81   * by this function. If the argument is omitted,
    82   * it returns the length of the string-value of the context node.
    83   * </p>
    84   *
    85   * @author bob mcwhirter (bob @ werken.com)
    86   * @see <a href="http://www.w3.org/TR/xpath#function-string-length" target="_top">Section
    87   *      4.2 of the XPath Specification</a>
    88   */
    89  public class StringLengthFunction implements Function
    90  {
    91
    92
    93      /***
    94       * Create a new <code>StringLengthFunction</code> object.
    95       */
    96      public StringLengthFunction() {}
    97
    98
    99      /***
    100      * <p>
    101      * Returns the number of Unicode characters in the string-value of the argument.
    102      * </p>
    103      *
    104      * @param context the context at the point in the
    105      *         expression when the function is called
    106      * @param args a list containing the item whose string-value is to be counted.
    107      *     If empty, the length of the context node's string-value is returned.
    108      *
    109      * @return a <code>Double</code> giving the number of Unicode characters
    110      *
    111      * @throws FunctionCallException if args has more than one item
    112      */
    113     public Object call(Context context,
    114                        List args) throws FunctionCallException
    115     {
    116         if (args.size() == 0)
    117         {
    118             return evaluate( context.getNodeSet(),
    119                              context.getNavigator() );
    120         }
    121         else if (args.size() == 1)
    122         {
    123             return evaluate( args.get(0),
    124                              context.getNavigator() );
    125         }
    126
    127         throw new FunctionCallException( "string-length() requires one argument." );
    128     }
    129
    130     /***
    131      * <p>
    132      * Returns the number of Unicode characters in the string-value of
    133      * an object.
    134      * </p>
    135      *
    136      * @param obj the object whose string-value is counted
    137      * @param nav used to calculate the string-values of the first two arguments
    138      *
    139      * @return a <code>Double</code> giving the number of Unicode characters
    140      *
    141      * @throws FunctionCallException if the string contains mismatched surrogates
    142      */
    143     public static Double evaluate(Object obj, Navigator nav) throws FunctionCallException
    144     {
    145
    146         // could/should I push the mismnatching checks into StringFunction.evaluate()????
    147         String str = StringFunction.evaluate( obj, nav );
    148         // String.length() counts UTF-16 code points; not Unicode characters
    149         char[] data = str.toCharArray();
    150         int length = 0;
    151         for (int i = 0; i < data.length; i++) {
    152             char c = data[i];
    153             length++;
    154             // if this is a high surrogate; assume the next character is
    155             // is a low surrogate and skip it
    156             if (c >= 0xD800) {
    157                 try {
    158                     char low = data[i+1];
    159                     if (low < 0xDC00 || low > 0xDFFF) {
    160                         throw new FunctionCallException("Bad surrogate pair in string " + str);
    161                     }
    162                     i++; // increment past low surrogate
    163                 }
    164                 catch (ArrayIndexOutOfBoundsException ex) {
    165                     throw new FunctionCallException("Bad surrogate pair in string " + str);
    166                 }
    167             }
    168         }
    169         return new Double(length);
    170     }
    171
    172 }