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Apache Commons Text is a library focused on algorithms working on strings.
/*
* 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.text;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.ThreadLocalRandom;
import org.apache.commons.lang3.ArrayUtils;
import org.apache.commons.lang3.StringUtils;
import org.apache.commons.lang3.Validate;
/**
* Generates random Unicode strings containing the specified number of code points.
* Instances are created using a builder class, which allows the
* callers to define the properties of the generator. See the documentation for the
* {@link Builder} class to see available properties.
*
*
* // Generates a 20 code point string, using only the letters a-z
* RandomStringGenerator generator = new RandomStringGenerator.Builder()
* .withinRange('a', 'z').build();
* String randomLetters = generator.generate(20);
*
*
* // Using Apache Commons RNG for randomness
* UniformRandomProvider rng = RandomSource.create(...);
* // Generates a 20 code point string, using only the letters a-z
* RandomStringGenerator generator = new RandomStringGenerator.Builder()
* .withinRange('a', 'z')
* .usingRandom(rng::nextInt) // uses Java 8 syntax
* .build();
* String randomLetters = generator.generate(20);
*
*
* {@code RandomStringGenerator} instances are thread-safe when using the
* default random number generator (RNG). If a custom RNG is set by calling the method
* {@link Builder#usingRandom(TextRandomProvider) Builder.usingRandom(TextRandomProvider)}, thread-safety
* must be ensured externally.
*
* @since 1.1
*/
public final class RandomStringGenerator {
/**
* A builder for generating {@code RandomStringGenerator} instances.
*
* The behavior of a generator is controlled by properties set by this
* builder. Each property has a default value, which can be overridden by
* calling the methods defined in this class, prior to calling {@link #build()}.
*
* All the property setting methods return the {@code Builder} instance to allow for method chaining.
*
* The minimum and maximum code point values are defined using {@link #withinRange(int, int)}. The
* default values are {@code 0} and {@link Character#MAX_CODE_POINT} respectively.
*
* The source of randomness can be set using {@link #usingRandom(TextRandomProvider)},
* otherwise {@link ThreadLocalRandom} is used.
*
* The type of code points returned can be filtered using {@link #filteredBy(CharacterPredicate...)},
* which defines a collection of tests that are applied to the randomly generated code points.
* The code points will only be included in the result if they pass at least one of the tests.
* Some commonly used predicates are provided by the {@link CharacterPredicates} enum.
*
* This class is not thread safe.
* @since 1.1
*/
public static class Builder implements org.apache.commons.text.Builder {
/**
* The default maximum code point allowed: {@link Character#MAX_CODE_POINT}
* ({@value}).
*/
public static final int DEFAULT_MAXIMUM_CODE_POINT = Character.MAX_CODE_POINT;
/**
* The default string length produced by this builder: {@value}.
*/
public static final int DEFAULT_LENGTH = 0;
/**
* The default minimum code point allowed: {@value}.
*/
public static final int DEFAULT_MINIMUM_CODE_POINT = 0;
/**
* The minimum code point allowed.
*/
private int minimumCodePoint = DEFAULT_MINIMUM_CODE_POINT;
/**
* The maximum code point allowed.
*/
private int maximumCodePoint = DEFAULT_MAXIMUM_CODE_POINT;
/**
* Filters for code points.
*/
private Set inclusivePredicates;
/**
* The source of randomness.
*/
private TextRandomProvider random;
/**
* The source of provided characters.
*/
private List characterList;
/**
* Builds the {@code RandomStringGenerator} using the properties specified.
*
* @return The configured {@code RandomStringGenerator}
*/
@Override
public RandomStringGenerator build() {
return new RandomStringGenerator(minimumCodePoint, maximumCodePoint, inclusivePredicates,
random, characterList);
}
/**
* Limits the characters in the generated string to those that match at
* least one of the predicates supplied.
*
*
* Passing {@code null} or an empty array to this method will revert to the
* default behavior of allowing any character. Multiple calls to this
* method will replace the previously stored predicates.
*
*
* @param predicates
* the predicates, may be {@code null} or empty
* @return {@code this}, to allow method chaining
*/
public Builder filteredBy(final CharacterPredicate... predicates) {
if (ArrayUtils.isEmpty(predicates)) {
inclusivePredicates = null;
return this;
}
if (inclusivePredicates == null) {
inclusivePredicates = new HashSet<>();
} else {
inclusivePredicates.clear();
}
Collections.addAll(inclusivePredicates, predicates);
return this;
}
/**
* Limits the characters in the generated string to those who match at
* supplied list of Character.
*
*
* Passing {@code null} or an empty array to this method will revert to the
* default behavior of allowing any character. Multiple calls to this
* method will replace the previously stored Character.
*
*
* @param chars set of predefined Characters for random string generation
* the Character can be, may be {@code null} or empty
* @return {@code this}, to allow method chaining
* @since 1.2
*/
public Builder selectFrom(final char... chars) {
characterList = new ArrayList<>();
for (final char c : chars) {
characterList.add(c);
}
return this;
}
/**
* Overrides the default source of randomness. It is highly
* recommended that a random number generator library like
* Apache Commons RNG
* be used to provide the random number generation.
*
*
* When using Java 8 or later, {@link TextRandomProvider} is a
* functional interface and need not be explicitly implemented:
*
*
* {@code
* UniformRandomProvider rng = RandomSource.create(...);
* RandomStringGenerator gen = new RandomStringGenerator.Builder()
* .usingRandom(rng::nextInt)
* // additional builder calls as needed
* .build();
* }
*
*
*
* Passing {@code null} to this method will revert to the default source of
* randomness.
*
*
* @param random
* the source of randomness, may be {@code null}
* @return {@code this}, to allow method chaining
*/
public Builder usingRandom(final TextRandomProvider random) {
this.random = random;
return this;
}
/**
* Sets the array of minimum and maximum char allowed in the
* generated string.
*
* For example:
*
* {@code
* char [][] pairs = {{'0','9'}};
* char [][] pairs = {{'a','z'}};
* char [][] pairs = {{'a','z'},{'0','9'}};
* }
*
*
* @param pairs array of characters array, expected is to pass min, max pairs through this arg.
* @return {@code this}, to allow method chaining.
*/
public Builder withinRange(final char[]... pairs) {
characterList = new ArrayList<>();
for (final char[] pair : pairs) {
Validate.isTrue(pair.length == 2,
"Each pair must contain minimum and maximum code point");
final int minimumCodePoint = pair[0];
final int maximumCodePoint = pair[1];
Validate.isTrue(minimumCodePoint <= maximumCodePoint,
"Minimum code point %d is larger than maximum code point %d", minimumCodePoint, maximumCodePoint);
for (int index = minimumCodePoint; index <= maximumCodePoint; index++) {
characterList.add((char) index);
}
}
return this;
}
/**
* Sets the minimum and maximum code points allowed in the
* generated string.
*
* @param minimumCodePoint
* the smallest code point allowed (inclusive)
* @param maximumCodePoint
* the largest code point allowed (inclusive)
* @return {@code this}, to allow method chaining
* @throws IllegalArgumentException
* if {@code maximumCodePoint >}
* {@link Character#MAX_CODE_POINT}
* @throws IllegalArgumentException
* if {@code minimumCodePoint < 0}
* @throws IllegalArgumentException
* if {@code minimumCodePoint > maximumCodePoint}
*/
public Builder withinRange(final int minimumCodePoint, final int maximumCodePoint) {
Validate.isTrue(minimumCodePoint <= maximumCodePoint,
"Minimum code point %d is larger than maximum code point %d", minimumCodePoint, maximumCodePoint);
Validate.isTrue(minimumCodePoint >= 0, "Minimum code point %d is negative", minimumCodePoint);
Validate.isTrue(maximumCodePoint <= Character.MAX_CODE_POINT,
"Value %d is larger than Character.MAX_CODE_POINT.", maximumCodePoint);
this.minimumCodePoint = minimumCodePoint;
this.maximumCodePoint = maximumCodePoint;
return this;
}
}
/**
* The smallest allowed code point (inclusive).
*/
private final int minimumCodePoint;
/**
* The largest allowed code point (inclusive).
*/
private final int maximumCodePoint;
/**
* Filters for code points.
*/
private final Set inclusivePredicates;
/**
* The source of randomness for this generator.
*/
private final TextRandomProvider random;
/**
* The source of provided characters.
*/
private final List characterList;
/**
* Constructs the generator.
*
* @param minimumCodePoint
* smallest allowed code point (inclusive)
* @param maximumCodePoint
* largest allowed code point (inclusive)
* @param inclusivePredicates
* filters for code points
* @param random
* source of randomness
* @param characterList list of predefined set of characters.
*/
private RandomStringGenerator(final int minimumCodePoint, final int maximumCodePoint,
final Set inclusivePredicates, final TextRandomProvider random,
final List characterList) {
this.minimumCodePoint = minimumCodePoint;
this.maximumCodePoint = maximumCodePoint;
this.inclusivePredicates = inclusivePredicates;
this.random = random;
this.characterList = characterList;
}
/**
* Generates a random string, containing the specified number of code points.
*
*
* Code points are randomly selected between the minimum and maximum values defined
* in the generator.
* Surrogate and private use characters are not returned, although the
* resulting string may contain pairs of surrogates that together encode a
* supplementary character.
*
*
* Note: the number of {@code char} code units generated will exceed
* {@code length} if the string contains supplementary characters. See the
* {@link Character} documentation to understand how Java stores Unicode
* values.
*
*
* @param length
* the number of code points to generate
* @return The generated string
* @throws IllegalArgumentException
* if {@code length < 0}
*/
public String generate(final int length) {
if (length == 0) {
return StringUtils.EMPTY;
}
Validate.isTrue(length > 0, "Length %d is smaller than zero.", length);
final StringBuilder builder = new StringBuilder(length);
long remaining = length;
do {
final int codePoint;
if (characterList != null && !characterList.isEmpty()) {
codePoint = generateRandomNumber(characterList);
} else {
codePoint = generateRandomNumber(minimumCodePoint, maximumCodePoint);
}
switch (Character.getType(codePoint)) {
case Character.UNASSIGNED:
case Character.PRIVATE_USE:
case Character.SURROGATE:
continue;
default:
}
if (inclusivePredicates != null) {
boolean matchedFilter = false;
for (final CharacterPredicate predicate : inclusivePredicates) {
if (predicate.test(codePoint)) {
matchedFilter = true;
break;
}
}
if (!matchedFilter) {
continue;
}
}
builder.appendCodePoint(codePoint);
remaining--;
} while (remaining != 0);
return builder.toString();
}
/**
* Generates a random string, containing between the minimum (inclusive) and the maximum (inclusive)
* number of code points.
*
* @param minLengthInclusive
* the minimum (inclusive) number of code points to generate
* @param maxLengthInclusive
* the maximum (inclusive) number of code points to generate
* @return The generated string
* @throws IllegalArgumentException
* if {@code minLengthInclusive < 0}, or {@code maxLengthInclusive < minLengthInclusive}
* @see RandomStringGenerator#generate(int)
* @since 1.2
*/
public String generate(final int minLengthInclusive, final int maxLengthInclusive) {
Validate.isTrue(minLengthInclusive >= 0, "Minimum length %d is smaller than zero.", minLengthInclusive);
Validate.isTrue(minLengthInclusive <= maxLengthInclusive,
"Maximum length %d is smaller than minimum length %d.", maxLengthInclusive, minLengthInclusive);
return generate(generateRandomNumber(minLengthInclusive, maxLengthInclusive));
}
/**
* Generates a random number within a range, using a {@link ThreadLocalRandom} instance
* or the user-supplied source of randomness.
*
* @param minInclusive
* the minimum value allowed
* @param maxInclusive
* the maximum value allowed
* @return The random number.
*/
private int generateRandomNumber(final int minInclusive, final int maxInclusive) {
if (random != null) {
return random.nextInt(maxInclusive - minInclusive + 1) + minInclusive;
}
return ThreadLocalRandom.current().nextInt(minInclusive, maxInclusive + 1);
}
/**
* Generates a random number within a range, using a {@link ThreadLocalRandom} instance
* or the user-supplied source of randomness.
*
* @param characterList predefined char list.
* @return The random number.
*/
private int generateRandomNumber(final List characterList) {
final int listSize = characterList.size();
if (random != null) {
return String.valueOf(characterList.get(random.nextInt(listSize))).codePointAt(0);
}
return String.valueOf(characterList.get(ThreadLocalRandom.current().nextInt(0, listSize))).codePointAt(0);
}
}