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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;
18  
19  import java.util.Random;
20  
21  /**
22   * <p>Operations for random {@code String}s.</p>
23   * <p>Currently <em>private high surrogate</em> characters are ignored. 
24   * These are Unicode characters that fall between the values 56192 (db80)
25   * and 56319 (dbff) as we don't know how to handle them. 
26   * High and low surrogates are correctly dealt with - that is if a 
27   * high surrogate is randomly chosen, 55296 (d800) to 56191 (db7f) 
28   * then it is followed by a low surrogate. If a low surrogate is chosen, 
29   * 56320 (dc00) to 57343 (dfff) then it is placed after a randomly 
30   * chosen high surrogate. </p>
31   *
32   * <p>#ThreadSafe#</p>
33   * @since 1.0
34   * @version $Id: RandomStringUtils.java 1532684 2013-10-16 08:28:42Z bayard $
35   */
36  public class RandomStringUtils {
37  
38      /**
39       * <p>Random object used by random method. This has to be not local
40       * to the random method so as to not return the same value in the 
41       * same millisecond.</p>
42       */
43      private static final Random RANDOM = new Random();
44  
45      /**
46       * <p>{@code RandomStringUtils} instances should NOT be constructed in
47       * standard programming. Instead, the class should be used as
48       * {@code RandomStringUtils.random(5);}.</p>
49       *
50       * <p>This constructor is public to permit tools that require a JavaBean instance
51       * to operate.</p>
52       */
53      public RandomStringUtils() {
54        super();
55      }
56  
57      // Random
58      //-----------------------------------------------------------------------
59      /**
60       * <p>Creates a random string whose length is the number of characters
61       * specified.</p>
62       *
63       * <p>Characters will be chosen from the set of all characters.</p>
64       *
65       * @param count  the length of random string to create
66       * @return the random string
67       */
68      public static String random(final int count) {
69          return random(count, false, false);
70      }
71  
72      /**
73       * <p>Creates a random string whose length is the number of characters
74       * specified.</p>
75       *
76       * <p>Characters will be chosen from the set of characters whose
77       * ASCII value is between {@code 32} and {@code 126} (inclusive).</p>
78       *
79       * @param count  the length of random string to create
80       * @return the random string
81       */
82      public static String randomAscii(final int count) {
83          return random(count, 32, 127, false, false);
84      }
85      
86      /**
87       * <p>Creates a random string whose length is the number of characters
88       * specified.</p>
89       *
90       * <p>Characters will be chosen from the set of alphabetic
91       * characters.</p>
92       *
93       * @param count  the length of random string to create
94       * @return the random string
95       */
96      public static String randomAlphabetic(final int count) {
97          return random(count, true, false);
98      }
99      
100     /**
101      * <p>Creates a random string whose length is the number of characters
102      * specified.</p>
103      *
104      * <p>Characters will be chosen from the set of alpha-numeric
105      * characters.</p>
106      *
107      * @param count  the length of random string to create
108      * @return the random string
109      */
110     public static String randomAlphanumeric(final int count) {
111         return random(count, true, true);
112     }
113     
114     /**
115      * <p>Creates a random string whose length is the number of characters
116      * specified.</p>
117      *
118      * <p>Characters will be chosen from the set of numeric
119      * characters.</p>
120      *
121      * @param count  the length of random string to create
122      * @return the random string
123      */
124     public static String randomNumeric(final int count) {
125         return random(count, false, true);
126     }
127 
128     /**
129      * <p>Creates a random string whose length is the number of characters
130      * specified.</p>
131      *
132      * <p>Characters will be chosen from the set of alpha-numeric
133      * characters as indicated by the arguments.</p>
134      *
135      * @param count  the length of random string to create
136      * @param letters  if {@code true}, generated string may include
137      *  alphabetic characters
138      * @param numbers  if {@code true}, generated string may include
139      *  numeric characters
140      * @return the random string
141      */
142     public static String random(final int count, final boolean letters, final boolean numbers) {
143         return random(count, 0, 0, letters, numbers);
144     }
145     
146     /**
147      * <p>Creates a random string whose length is the number of characters
148      * specified.</p>
149      *
150      * <p>Characters will be chosen from the set of alpha-numeric
151      * characters as indicated by the arguments.</p>
152      *
153      * @param count  the length of random string to create
154      * @param start  the position in set of chars to start at
155      * @param end  the position in set of chars to end before
156      * @param letters  if {@code true}, generated string may include
157      *  alphabetic characters
158      * @param numbers  if {@code true}, generated string may include
159      *  numeric characters
160      * @return the random string
161      */
162     public static String random(final int count, final int start, final int end, final boolean letters, final boolean numbers) {
163         return random(count, start, end, letters, numbers, null, RANDOM);
164     }
165 
166     /**
167      * <p>Creates a random string based on a variety of options, using
168      * default source of randomness.</p>
169      *
170      * <p>This method has exactly the same semantics as
171      * {@link #random(int,int,int,boolean,boolean,char[],Random)}, but
172      * instead of using an externally supplied source of randomness, it uses
173      * the internal static {@link Random} instance.</p>
174      *
175      * @param count  the length of random string to create
176      * @param start  the position in set of chars to start at
177      * @param end  the position in set of chars to end before
178      * @param letters  only allow letters?
179      * @param numbers  only allow numbers?
180      * @param chars  the set of chars to choose randoms from.
181      *  If {@code null}, then it will use the set of all chars.
182      * @return the random string
183      * @throws ArrayIndexOutOfBoundsException if there are not
184      *  {@code (end - start) + 1} characters in the set array.
185      */
186     public static String random(final int count, final int start, final int end, final boolean letters, final boolean numbers, final char... chars) {
187         return random(count, start, end, letters, numbers, chars, RANDOM);
188     }
189 
190     /**
191      * <p>Creates a random string based on a variety of options, using
192      * supplied source of randomness.</p>
193      *
194      * <p>If start and end are both {@code 0}, start and end are set
195      * to {@code ' '} and {@code 'z'}, the ASCII printable
196      * characters, will be used, unless letters and numbers are both
197      * {@code false}, in which case, start and end are set to
198      * {@code 0} and {@code Integer.MAX_VALUE}.
199      *
200      * <p>If set is not {@code null}, characters between start and
201      * end are chosen.</p>
202      *
203      * <p>This method accepts a user-supplied {@link Random}
204      * instance to use as a source of randomness. By seeding a single 
205      * {@link Random} instance with a fixed seed and using it for each call,
206      * the same random sequence of strings can be generated repeatedly
207      * and predictably.</p>
208      *
209      * @param count  the length of random string to create
210      * @param start  the position in set of chars to start at
211      * @param end  the position in set of chars to end before
212      * @param letters  only allow letters?
213      * @param numbers  only allow numbers?
214      * @param chars  the set of chars to choose randoms from, must not be empty.
215      *  If {@code null}, then it will use the set of all chars.
216      * @param random  a source of randomness.
217      * @return the random string
218      * @throws ArrayIndexOutOfBoundsException if there are not
219      *  {@code (end - start) + 1} characters in the set array.
220      * @throws IllegalArgumentException if {@code count} &lt; 0 or the provided chars array is empty.
221      * @since 2.0
222      */
223     public static String random(int count, int start, int end, final boolean letters, final boolean numbers,
224                                 final char[] chars, final Random random) {
225         if (count == 0) {
226             return "";
227         } else if (count < 0) {
228             throw new IllegalArgumentException("Requested random string length " + count + " is less than 0.");
229         }
230         if (chars != null && chars.length == 0) {
231             throw new IllegalArgumentException("The chars array must not be empty");
232         }
233 
234         if (start == 0 && end == 0) {
235             if (chars != null) {
236                 end = chars.length;
237             } else {
238                 if (!letters && !numbers) {
239                     end = Integer.MAX_VALUE;
240                 } else {
241                     end = 'z' + 1;
242                     start = ' ';                
243                 }
244             }
245         } else {
246             if (end <= start) {
247                 throw new IllegalArgumentException("Parameter end (" + end + ") must be greater than start (" + start + ")");
248             }
249         }
250 
251         final char[] buffer = new char[count];
252         final int gap = end - start;
253 
254         while (count-- != 0) {
255             char ch;
256             if (chars == null) {
257                 ch = (char) (random.nextInt(gap) + start);
258             } else {
259                 ch = chars[random.nextInt(gap) + start];
260             }
261             if (letters && Character.isLetter(ch)
262                     || numbers && Character.isDigit(ch)
263                     || !letters && !numbers) {
264                 if(ch >= 56320 && ch <= 57343) {
265                     if(count == 0) {
266                         count++;
267                     } else {
268                         // low surrogate, insert high surrogate after putting it in
269                         buffer[count] = ch;
270                         count--;
271                         buffer[count] = (char) (55296 + random.nextInt(128));
272                     }
273                 } else if(ch >= 55296 && ch <= 56191) {
274                     if(count == 0) {
275                         count++;
276                     } else {
277                         // high surrogate, insert low surrogate before putting it in
278                         buffer[count] = (char) (56320 + random.nextInt(128));
279                         count--;
280                         buffer[count] = ch;
281                     }
282                 } else if(ch >= 56192 && ch <= 56319) {
283                     // private high surrogate, no effing clue, so skip it
284                     count++;
285                 } else {
286                     buffer[count] = ch;
287                 }
288             } else {
289                 count++;
290             }
291         }
292         return new String(buffer);
293     }
294 
295     /**
296      * <p>Creates a random string whose length is the number of characters
297      * specified.</p>
298      *
299      * <p>Characters will be chosen from the set of characters
300      * specified by the string, must not be empty. 
301      * If null, the set of all characters is used.</p>
302      *
303      * @param count  the length of random string to create
304      * @param chars  the String containing the set of characters to use,
305      *  may be null, but must not be empty
306      * @return the random string
307      * @throws IllegalArgumentException if {@code count} &lt; 0 or the string is empty.
308      */
309     public static String random(final int count, final String chars) {
310         if (chars == null) {
311             return random(count, 0, 0, false, false, null, RANDOM);
312         }
313         return random(count, chars.toCharArray());
314     }
315 
316     /**
317      * <p>Creates a random string whose length is the number of characters
318      * specified.</p>
319      *
320      * <p>Characters will be chosen from the set of characters specified.</p>
321      *
322      * @param count  the length of random string to create
323      * @param chars  the character array containing the set of characters to use,
324      *  may be null
325      * @return the random string
326      * @throws IllegalArgumentException if {@code count} &lt; 0.
327      */
328     public static String random(final int count, final char... chars) {
329         if (chars == null) {
330             return random(count, 0, 0, false, false, null, RANDOM);
331         }
332         return random(count, 0, chars.length, false, false, chars, RANDOM);
333     }
334     
335 }