Java example source code file (RandomStringUtils.java)

This example Java source code file (RandomStringUtils.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

illegalargumentexception, parameter, random, randomstringutils, requested, string, the, util

The RandomStringUtils.java Java example source code

/*
 * 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.
 */
package org.apache.commons.lang3;

import java.util.Random;

/**
 * <p>Operations for random {@code String}s.

 * <p>Currently private high surrogate 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. </p>
 *
 * <p>#ThreadSafe#

 * @since 1.0
 */
public class RandomStringUtils {

    /**
     * <p>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.</p>
     */
    private static final Random RANDOM = new Random();

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

    // Random
    //-----------------------------------------------------------------------
    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>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(final int count) {
        return random(count, false, false);
    }

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

     *
     * <p>Characters will be chosen from the set of characters which match the POSIX [:graph:]
     * regular expression character class. This class contains all visible ASCII characters 
     * (i.e. anything except spaces and control characters).</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     * @since 3.5
     */
    public static String randomGraph(final int count) {
        return random(count, 33, 126, false, false);
    }
    
    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of numeric
     * characters.</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     */
    public static String randomNumeric(final int count) {
        return random(count, false, true);
    }

    /**
     * <p>Creates a random string whose length is the number of characters specified.

     *
     * <p>Characters will be chosen from the set of characters which match the POSIX [:print:]
     * regular expression character class. This class includes all visible ASCII characters and spaces
     * (i.e. anything except control characters).</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     * @since 3.5
     */
    public static String randomPrint(final int count) {
        return random(count, 32, 126, false, false);
    }

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

    /**
     * <p>Creates a random string based on a variety of options, using
     * default source of randomness.</p>
     *
     * <p>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.</p>
     *
     * @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}, then it will use the set of all chars.
     * @return the random string
     * @throws ArrayIndexOutOfBoundsException if there are not
     *  {@code (end - start) + 1} characters in the set array.
     */
    public static String random(final int count, final int start, final int end, final boolean letters, final boolean numbers, final char... chars) {
        return random(count, start, end, letters, numbers, chars, RANDOM);
    }

    /**
     * <p>Creates a random string based on a variety of options, using
     * supplied source of randomness.</p>
     *
     * <p>If start and end are both {@code 0}, start and end are set
     * to {@code ' '} and {@code 'z'}, the ASCII printable
     * characters, will be used, unless letters and numbers are both
     * {@code false}, in which case, start and end are set to
     * {@code 0} and {@code Integer.MAX_VALUE}.
     *
     * <p>If set is not {@code null}, characters between start and
     * end are chosen.</p>
     *
     * <p>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.</p>
     *
     * @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, must not be empty.
     *  If {@code null}, 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} characters in the set array.
     * @throws IllegalArgumentException if {@code count} < 0 or the provided chars array is empty.
     * @since 2.0
     */
    public static String random(int count, int start, int end, final boolean letters, final boolean numbers,
                                final char[] chars, final Random random) {
        if (count == 0) {
            return StringUtils.EMPTY;
        } else if (count < 0) {
            throw new IllegalArgumentException("Requested random string length " + count + " is less than 0.");
        }
        if (chars != null && chars.length == 0) {
            throw new IllegalArgumentException("The chars array must not be empty");
        }

        if (start == 0 && end == 0) {
            if (chars != null) {
                end = chars.length;
            } else {
                if (!letters && !numbers) {
                    end = Integer.MAX_VALUE;
                } else {
                    end = 'z' + 1;
                    start = ' ';                
                }
            }
        } else {
            if (end <= start) {
                throw new IllegalArgumentException("Parameter end (" + end + ") must be greater than start (" + start + ")");
            }
        }

        final char[] buffer = new char[count];
        final 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);
    }

    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of characters
     * specified by the string, must not be empty. 
     * If null, the set of all characters is used.</p>
     *
     * @param count  the length of random string to create
     * @param chars  the String containing the set of characters to use,
     *  may be null, but must not be empty
     * @return the random string
     * @throws IllegalArgumentException if {@code count} < 0 or the string is empty.
     */
    public static String random(final int count, final String chars) {
        if (chars == null) {
            return random(count, 0, 0, false, false, null, RANDOM);
        }
        return random(count, chars.toCharArray());
    }

    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>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} < 0.
     */
    public static String random(final int count, final char... chars) {
        if (chars == null) {
            return random(count, 0, 0, false, false, null, RANDOM);
        }
        return random(count, 0, chars.length, false, false, chars, RANDOM);
    }
    
}