Generated Random Strings in Java

/*from  w ww  .  ja v a  2s.  co  m*/
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.util.Random;

public class Main {
  public static void main(String[] argv) {
    System.out.println(RandomStringUtils.randomAscii(10));
    System.out.println(RandomStringUtils.randomAscii(10));
    System.out.println(RandomStringUtils.randomAscii(10));
    System.out.println(RandomStringUtils.randomAscii(10));
    System.out.println(RandomStringUtils.randomAscii(10));
    System.out.println(RandomStringUtils.randomAscii(10));
    System.out.println(RandomStringUtils.randomAscii(10));
    System.out.println(RandomStringUtils.randomAscii(10));
  }
}

/**
 * Operations for random <code>String</code>s. Currently
 * <em>private high surrogate</em> characters are ignored. These are unicode
 * characters that fall between the values 56192 (db80) and 56319 (dbff) as we
 * don't know how to handle them. High and low surrogates are correctly dealt
 * with - that is if a high surrogate is randomly chosen, 55296 (d800) to 56191
 * (db7f) then it is followed by a low surrogate. If a low surrogate is chosen,
 * 56320 (dc00) to 57343 (dfff) then it is placed after a randomly chosen high
 * surrogate.
 * 
 * @author <a href="mailto:steven@caswell.name">Steven Caswell</a>
 * @author Stephen Colebourne
 * @author Gary Gregory
 * @author Phil Steitz
 * @since 1.0
 * @version $Id: RandomStringUtils.java 471626 2006-11-06 04:02:09Z bayard $
 */
class RandomStringUtils {

  /**
   * Random object used by random method. This has to be not local to the
   * random method so as to not return the same value in the same millisecond.
   */
  private static final Random RANDOM = new Random();

  /**
   * <code>RandomStringUtils</code> instances should NOT be constructed in
   * standard programming. Instead, the class should be used as
   * <code>RandomStringUtils.random(5);</code>.
   * 
   * This constructor is public to permit tools that require a JavaBean
   * instance to operate.
   */
  public RandomStringUtils() {
    super();
  }

  // Random
  // -----------------------------------------------------------------------
  /**
   * Creates a random string whose length is the number of characters
   * specified.
   * 
   * Characters will be chosen from the set of all characters.
   * 
   * @param count
   *            the length of random string to create
   * @return the random string
   */
  public static String random(int count) {
    return random(count, false, false);
  }

  /**
   * Creates a random string whose length is the number of characters
   * specified.
   * 
   * Characters will be chosen from the set of characters whose ASCII value is
   * between <code>32</code> and <code>126</code> (inclusive).
   * 
   * @param count
   *            the length of random string to create
   * @return the random string
   */
  public static String randomAscii(int count) {
    return random(count, 32, 127, false, false);
  }

  /**
   * Creates a random string whose length is the number of characters
   * specified.
   * 
   * Characters will be chosen from the set of alphabetic characters.
   * 
   * @param count
   *            the length of random string to create
   * @return the random string
   */
  public static String randomAlphabetic(int count) {
    return random(count, true, false);
  }

  /**
   * Creates a random string whose length is the number of characters
   * specified.
   * 
   * Characters will be chosen from the set of alpha-numeric characters.
   * 
   * @param count
   *            the length of random string to create
   * @return the random string
   */
  public static String randomAlphanumeric(int count) {
    return random(count, true, true);
  }

  /**
   * Creates a random string whose length is the number of characters
   * specified.
   * 
   * Characters will be chosen from the set of numeric characters.
   * 
   * @param count
   *            the length of random string to create
   * @return the random string
   */
  public static String randomNumeric(int count) {
    return random(count, false, true);
  }

  /**
   * Creates a random string whose length is the number of characters
   * specified.
   * 
   * Characters will be chosen from the set of alpha-numeric characters as
   * indicated by the arguments.
   * 
   * @param count
   *            the length of random string to create
   * @param letters
   *            if <code>true</code>, generated string will include alphabetic
   *            characters
   * @param numbers
   *            if <code>true</code>, generated string will include numeric
   *            characters
   * @return the random string
   */
  public static String random(int count, boolean letters, boolean numbers) {
    return random(count, 0, 0, letters, numbers);
  }

  /**
   * Creates a random string whose length is the number of characters
   * specified.
   * 
   * Characters will be chosen from the set of alpha-numeric characters as
   * indicated by the arguments.
   * 
   * @param count
   *            the length of random string to create
   * @param start
   *            the position in set of chars to start at
   * @param end
   *            the position in set of chars to end before
   * @param letters
   *            if <code>true</code>, generated string will include alphabetic
   *            characters
   * @param numbers
   *            if <code>true</code>, generated string will include numeric
   *            characters
   * @return the random string
   */
  public static String random(int count, int start, int end, boolean letters,
      boolean numbers) {
    return random(count, start, end, letters, numbers, null, RANDOM);
  }

  /**
   * Creates a random string based on a variety of options, using default
   * source of randomness.
   * 
   * This method has exactly the same semantics as
   * {@link #random(int,int,int,boolean,boolean,char[],Random)}, but instead
   * of using an externally supplied source of randomness, it uses the
   * internal static {@link Random} instance.
   * 
   * @param count
   *            the length of random string to create
   * @param start
   *            the position in set of chars to start at
   * @param end
   *            the position in set of chars to end before
   * @param letters
   *            only allow letters?
   * @param numbers
   *            only allow numbers?
   * @param chars
   *            the set of chars to choose randoms from. If <code>null</code>,
   *            then it will use the set of all chars.
   * @return the random string
   * @throws ArrayIndexOutOfBoundsException
   *             if there are not <code>(end - start) + 1</code> characters in
   *             the set array.
   */
  public static String random(int count, int start, int end, boolean letters,
      boolean numbers, char[] chars) {
    return random(count, start, end, letters, numbers, chars, RANDOM);
  }

  /**
   * Creates a random string based on a variety of options, using supplied
   * source of randomness.
   * 
   * If start and end are both <code>0</code>, start and end are set to
   * <code>' '</code> and <code>'z'</code>, the ASCII printable characters,
   * will be used, unless letters and numbers are both <code>false</code>, in
   * which case, start and end are set to <code>0</code> and
   * <code>Integer.MAX_VALUE</code>.
   * 
   * If set is not <code>null</code>, characters between start and end are
   * chosen.
   * 
   * This method accepts a user-supplied {@link Random} instance to use as a
   * source of randomness. By seeding a single {@link Random} instance with a
   * fixed seed and using it for each call, the same random sequence of
   * strings can be generated repeatedly and predictably.
   * 
   * @param count
   *            the length of random string to create
   * @param start
   *            the position in set of chars to start at
   * @param end
   *            the position in set of chars to end before
   * @param letters
   *            only allow letters?
   * @param numbers
   *            only allow numbers?
   * @param chars
   *            the set of chars to choose randoms from. If <code>null</code>,
   *            then it will use the set of all chars.
   * @param random
   *            a source of randomness.
   * @return the random string
   * @throws ArrayIndexOutOfBoundsException
   *             if there are not <code>(end - start) + 1</code> characters in
   *             the set array.
   * @throws IllegalArgumentException
   *             if <code>count</code> &lt; 0.
   * @since 2.0
   */
  public static String random(int count, int start, int end, boolean letters,
      boolean numbers, char[] chars, Random random) {
    if (count == 0) {
      return "";
    } else if (count < 0) {
      throw new IllegalArgumentException(
          "Requested random string length " + count
              + " is less than 0.");
    }
    if ((start == 0) && (end == 0)) {
      end = 'z' + 1;
      start = ' ';
      if (!letters && !numbers) {
        start = 0;
        end = Integer.MAX_VALUE;
      }
    }

    char[] buffer = new char[count];
    int gap = end - start;

    while (count-- != 0) {
      char ch;
      if (chars == null) {
        ch = (char) (random.nextInt(gap) + start);
      } else {
        ch = chars[random.nextInt(gap) + start];
      }
      if ((letters && Character.isLetter(ch))
          || (numbers && Character.isDigit(ch))
          || (!letters && !numbers)) {
        if (ch >= 56320 && ch <= 57343) {
          if (count == 0) {
            count++;
          } else {
            // low surrogate, insert high surrogate after putting it
            // in
            buffer[count] = ch;
            count--;
            buffer[count] = (char) (55296 + random.nextInt(128));
          }
        } else if (ch >= 55296 && ch <= 56191) {
          if (count == 0) {
            count++;
          } else {
            // high surrogate, insert low surrogate before putting
            // it in
            buffer[count] = (char) (56320 + random.nextInt(128));
            count--;
            buffer[count] = ch;
          }
        } else if (ch >= 56192 && ch <= 56319) {
          // private high surrogate, no effing clue, so skip it
          count++;
        } else {
          buffer[count] = ch;
        }
      } else {
        count++;
      }
    }
    return new String(buffer);
  }

  /**
   * Creates a random string whose length is the number of characters
   * specified.
   * 
   * Characters will be chosen from the set of characters specified.
   * 
   * @param count
   *            the length of random string to create
   * @param chars
   *            the String containing the set of characters to use, may be
   *            null
   * @return the random string
   * @throws IllegalArgumentException
   *             if <code>count</code> &lt; 0.
   */
  public static String random(int count, String chars) {
    if (chars == null) {
      return random(count, 0, 0, false, false, null, RANDOM);
    }
    return random(count, chars.toCharArray());
  }

  /**
   * Creates a random string whose length is the number of characters
   * specified.
   * 
   * Characters will be chosen from the set of characters specified.
   * 
   * @param count
   *            the length of random string to create
   * @param chars
   *            the character array containing the set of characters to use,
   *            may be null
   * @return the random string
   * @throws IllegalArgumentException
   *             if <code>count</code> &lt; 0.
   */
  public static String random(int count, char[] chars) {
    if (chars == null) {
      return random(count, 0, 0, false, false, null, RANDOM);
    }
    return random(count, 0, chars.length, false, false, chars, RANDOM);
  }

}