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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    * 
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   * 
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.lang3.text.translate;
18  
19  import java.io.IOException;
20  import java.io.Writer;
21  
22  /**
23   * Translates escaped Unicode values of the form \\u+\d\d\d\d back to 
24   * Unicode. It supports multiple 'u' characters and will work with or 
25   * without the +.
26   * 
27   * @since 3.0
28   * @version $Id: UnicodeUnescaper.java 1436770 2013-01-22 07:09:45Z ggregory $
29   */
30  public class UnicodeUnescaper extends CharSequenceTranslator {
31  
32      /**
33       * {@inheritDoc}
34       */
35      @Override
36      public int translate(final CharSequence input, final int index, final Writer out) throws IOException {
37          if (input.charAt(index) == '\\' && index + 1 < input.length() && input.charAt(index + 1) == 'u') {
38              // consume optional additional 'u' chars
39              int i = 2;
40              while (index + i < input.length() && input.charAt(index + i) == 'u') {
41                  i++;
42              }
43  
44              if (index + i < input.length() && input.charAt(index + i) == '+') {
45                  i++;
46              }
47  
48              if (index + i + 4 <= input.length()) {
49                  // Get 4 hex digits
50                  final CharSequence unicode = input.subSequence(index + i, index + i + 4);
51  
52                  try {
53                      final int value = Integer.parseInt(unicode.toString(), 16);
54                      out.write((char) value);
55                  } catch (final NumberFormatException nfe) {
56                      throw new IllegalArgumentException("Unable to parse unicode value: " + unicode, nfe);
57                  }
58                  return i + 4;
59              } else {
60                  throw new IllegalArgumentException("Less than 4 hex digits in unicode value: '" + input.subSequence(index, input.length())
61                          + "' due to end of CharSequence");
62              }
63          }
64          return 0;
65      }
66  }