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/*
* 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 com.feilong.lib.lang3;
import java.util.Random;
/**
*
* Generates random {@code String}s.
*
*
*
* Caveat: Instances of {@link Random}, upon which the implementation of this
* class relies, are not cryptographically secure.
*
*
*
* RandomStringUtils is intended for simple use cases. For more advanced
* use cases consider using Apache Commons Text's
*
* RandomStringGenerator instead.
*
*
*
* The Apache Commons project provides
* Commons RNG dedicated to pseudo-random number generation, that may be
* a better choice for applications with more stringent requirements
* (performance and/or correctness).
*
*
*
* Note that 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.
*
*
*
* #ThreadSafe#
*
*
* @since 1.0
*/
public 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} instances should NOT be constructed in
* standard programming. Instead, the class should be used as
* {@code RandomStringUtils.random(5);}.
*
*
*
* This constructor is public to permit tools that require a JavaBean instance
* to operate.
*
*/
public RandomStringUtils(){
super();
}
/**
*
* Creates a random string based on a variety of options, using
* supplied source of randomness.
*
*
*
* 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 {@link Character#MAX_CODE_POINT}.
*
*
* If set is not {@code null}, 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 (inclusive)
* @param end
* the position in set of chars to end before (exclusive)
* @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 "";
}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 = Character.MAX_CODE_POINT;
}else{
end = 'z' + 1;
start = ' ';
}
}
}else{
if (end <= start){
throw new IllegalArgumentException("Parameter end (" + end + ") must be greater than start (" + start + ")");
}
}
final int zero_digit_ascii = 48;
final int first_letter_ascii = 65;
if (chars == null && (numbers && end <= zero_digit_ascii || letters && end <= first_letter_ascii)){
throw new IllegalArgumentException(
"Parameter end (" + end + ") must be greater then (" + zero_digit_ascii + ") for generating digits "
+ "or greater then (" + first_letter_ascii + ") for generating letters.");
}
final StringBuilder builder = new StringBuilder(count);
final int gap = end - start;
while (count-- != 0){
int codePoint;
if (chars == null){
codePoint = random.nextInt(gap) + start;
switch (Character.getType(codePoint)) {
case Character.UNASSIGNED:
case Character.PRIVATE_USE:
case Character.SURROGATE:
count++;
continue;
}
}else{
codePoint = chars[random.nextInt(gap) + start];
}
final int numberOfChars = Character.charCount(codePoint);
if (count == 0 && numberOfChars > 1){
count++;
continue;
}
if (letters && Character.isLetter(codePoint) || numbers && Character.isDigit(codePoint) || !letters && !numbers){
builder.appendCodePoint(codePoint);
if (numberOfChars == 2){
count--;
}
}else{
count++;
}
}
return builder.toString();
}
/**
*
* Creates a random string whose length is the number of characters
* specified.
*
*
*
* 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.
*
*
* @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());
}
/**
*
* 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} < 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);
}
}