    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.text;
    018
    019import java.util.ArrayList;
    020import java.util.Collections;
    021import java.util.HashSet;
    022import java.util.List;
    023import java.util.Set;
    024import java.util.concurrent.ThreadLocalRandom;
    025
    026import org.apache.commons.lang3.ArrayUtils;
    027import org.apache.commons.lang3.StringUtils;
    028import org.apache.commons.lang3.Validate;
    029
    030/**
    031 * Generates random Unicode strings containing the specified number of code points.
    032 * Instances are created using a builder class, which allows the
    033 * callers to define the properties of the generator. See the documentation for the
    034 * {@link Builder} class to see available properties.
    035 *
    036 * <pre>
    037 * // Generates a 20 code point string, using only the letters a-z
    038 * RandomStringGenerator generator = RandomStringGenerator.builder()
    039 *     .withinRange('a', 'z').build();
    040 * String randomLetters = generator.generate(20);
    041 * </pre>
    042 * <pre>
    043 * // Using Apache Commons RNG for randomness
    044 * UniformRandomProvider rng = RandomSource.create(...);
    045 * // Generates a 20 code point string, using only the letters a-z
    046 * RandomStringGenerator generator = RandomStringGenerator.builder()
    047 *     .withinRange('a', 'z')
    048 *     .usingRandom(rng::nextInt) // uses Java 8 syntax
    049 *     .build();
    050 * String randomLetters = generator.generate(20);
    051 * </pre>
    052 * <p>
    053 * {@code RandomStringGenerator} instances are thread-safe when using the
    054 * default random number generator (RNG). If a custom RNG is set by calling the method
    055 * {@link Builder#usingRandom(TextRandomProvider) Builder.usingRandom(TextRandomProvider)}, thread-safety
    056 * must be ensured externally.
    057 * </p>
    058 * @since 1.1
    059 */
    060public final class RandomStringGenerator {
    061
    062    /**
    063     * A builder for generating {@code RandomStringGenerator} instances.
    064     *
    065     * <p>The behavior of a generator is controlled by properties set by this
    066     * builder. Each property has a default value, which can be overridden by
    067     * calling the methods defined in this class, prior to calling {@link #build()}.</p>
    068     *
    069     * <p>All the property setting methods return the {@code Builder} instance to allow for method chaining.</p>
    070     *
    071     * <p>The minimum and maximum code point values are defined using {@link #withinRange(int, int)}. The
    072     * default values are {@code 0} and {@link Character#MAX_CODE_POINT} respectively.</p>
    073     *
    074     * <p>The source of randomness can be set using {@link #usingRandom(TextRandomProvider)},
    075     * otherwise {@link ThreadLocalRandom} is used.</p>
    076     *
    077     * <p>The type of code points returned can be filtered using {@link #filteredBy(CharacterPredicate...)},
    078     * which defines a collection of tests that are applied to the randomly generated code points.
    079     * The code points will only be included in the result if they pass at least one of the tests.
    080     * Some commonly used predicates are provided by the {@link CharacterPredicates} enum.</p>
    081     *
    082     * <p>This class is not thread safe.</p>
    083     * @since 1.1
    084     */
    085    public static class Builder implements org.apache.commons.text.Builder<RandomStringGenerator> {
    086
    087        /**
    088         * The default maximum code point allowed: {@link Character#MAX_CODE_POINT}
    089         * ({@value}).
    090         */
    091        public static final int DEFAULT_MAXIMUM_CODE_POINT = Character.MAX_CODE_POINT;
    092
    093        /**
    094         * The default string length produced by this builder: {@value}.
    095         */
    096        public static final int DEFAULT_LENGTH = 0;
    097
    098        /**
    099         * The default minimum code point allowed: {@value}.
    100         */
    101        public static final int DEFAULT_MINIMUM_CODE_POINT = 0;
    102
    103        /**
    104         * The minimum code point allowed.
    105         */
    106        private int minimumCodePoint = DEFAULT_MINIMUM_CODE_POINT;
    107
    108        /**
    109         * The maximum code point allowed.
    110         */
    111        private int maximumCodePoint = DEFAULT_MAXIMUM_CODE_POINT;
    112
    113        /**
    114         * Filters for code points.
    115         */
    116        private Set<CharacterPredicate> inclusivePredicates;
    117
    118        /**
    119         * The source of randomness.
    120         */
    121        private TextRandomProvider random;
    122
    123        /**
    124         * The source of provided characters.
    125         */
    126        private List<Character> characterList;
    127
    128        /**
    129         * Builds a new {@code RandomStringGenerator}.
    130         *
    131         * @return A new {@code RandomStringGenerator}
    132         * @deprecated Use {@link #get()}.
    133         */
    134        @Deprecated
    135        @Override
    136        public RandomStringGenerator build() {
    137            return get();
    138        }
    139
    140        /**
    141         * Limits the characters in the generated string to those that match at
    142         * least one of the predicates supplied.
    143         *
    144         * <p>
    145         * Passing {@code null} or an empty array to this method will revert to the
    146         * default behavior of allowing any character. Multiple calls to this
    147         * method will replace the previously stored predicates.
    148         * </p>
    149         *
    150         * @param predicates
    151         *            the predicates, may be {@code null} or empty
    152         * @return {@code this}, to allow method chaining
    153         */
    154        public Builder filteredBy(final CharacterPredicate... predicates) {
    155            if (ArrayUtils.isEmpty(predicates)) {
    156                inclusivePredicates = null;
    157                return this;
    158            }
    159            if (inclusivePredicates == null) {
    160                inclusivePredicates = new HashSet<>();
    161            } else {
    162                inclusivePredicates.clear();
    163            }
    164            Collections.addAll(inclusivePredicates, predicates);
    165            return this;
    166        }
    167
    168        /**
    169         * Builds a new {@code RandomStringGenerator}.
    170         *
    171         * @return A new {@code RandomStringGenerator}
    172         * @since 1.12.0
    173         */
    174        @Override
    175        public RandomStringGenerator get() {
    176            return new RandomStringGenerator(minimumCodePoint, maximumCodePoint, inclusivePredicates,
    177                    random, characterList);
    178        }
    179
    180        /**
    181         * Limits the characters in the generated string to those who match at
    182         * supplied list of Character.
    183         *
    184         * <p>
    185         * Passing {@code null} or an empty array to this method will revert to the
    186         * default behavior of allowing any character. Multiple calls to this
    187         * method will replace the previously stored Character.
    188         * </p>
    189         *
    190         * @param chars set of predefined Characters for random string generation
    191         *            the Character can be, may be {@code null} or empty
    192         * @return {@code this}, to allow method chaining
    193         * @since 1.2
    194         */
    195        public Builder selectFrom(final char... chars) {
    196            characterList = new ArrayList<>();
    197            if (chars != null) {
    198                for (final char c : chars) {
    199                    characterList.add(c);
    200                }
    201            }
    202            return this;
    203        }
    204
    205        /**
    206         * Overrides the default source of randomness.  It is highly
    207         * recommended that a random number generator library like
    208         * <a href="https://commons.apache.org/proper/commons-rng/">Apache Commons RNG</a>
    209         * be used to provide the random number generation.
    210         *
    211         * <p>
    212         * When using Java 8 or later, {@link TextRandomProvider} is a
    213         * functional interface and need not be explicitly implemented:
    214         * </p>
    215         * <pre>
    216         * {@code
    217         *     UniformRandomProvider rng = RandomSource.create(...);
    218         *     RandomStringGenerator gen = RandomStringGenerator.builder()
    219         *         .usingRandom(rng::nextInt)
    220         *         // additional builder calls as needed
    221         *         .build();
    222         * }
    223         * </pre>
    224         *
    225         * <p>
    226         * Passing {@code null} to this method will revert to the default source of
    227         * randomness.
    228         * </p>
    229         *
    230         * @param random
    231         *            the source of randomness, may be {@code null}
    232         * @return {@code this}, to allow method chaining
    233         */
    234        public Builder usingRandom(final TextRandomProvider random) {
    235            this.random = random;
    236            return this;
    237        }
    238
    239        /**
    240         * Sets the array of minimum and maximum char allowed in the
    241         * generated string.
    242         *
    243         * For example:
    244         * <pre>
    245         * {@code
    246         *     char [][] pairs = {{'0','9'}};
    247         *     char [][] pairs = {{'a','z'}};
    248         *     char [][] pairs = {{'a','z'},{'0','9'}};
    249         * }
    250         * </pre>
    251         *
    252         * @param pairs array of characters array, expected is to pass min, max pairs through this arg.
    253         * @return {@code this}, to allow method chaining.
    254         */
    255        public Builder withinRange(final char[]... pairs) {
    256            characterList = new ArrayList<>();
    257            if (pairs != null) {
    258                for (final char[] pair : pairs) {
    259                    Validate.isTrue(pair.length == 2, "Each pair must contain minimum and maximum code point");
    260                    final int minimumCodePoint = pair[0];
    261                    final int maximumCodePoint = pair[1];
    262                    Validate.isTrue(minimumCodePoint <= maximumCodePoint, "Minimum code point %d is larger than maximum code point %d", minimumCodePoint,
    263                            maximumCodePoint);
    264
    265                    for (int index = minimumCodePoint; index <= maximumCodePoint; index++) {
    266                        characterList.add((char) index);
    267                    }
    268                }
    269            }
    270            return this;
    271
    272        }
    273
    274        /**
    275         * Sets the minimum and maximum code points allowed in the
    276         * generated string.
    277         *
    278         * @param minimumCodePoint
    279         *            the smallest code point allowed (inclusive)
    280         * @param maximumCodePoint
    281         *            the largest code point allowed (inclusive)
    282         * @return {@code this}, to allow method chaining
    283         * @throws IllegalArgumentException
    284         *             if {@code maximumCodePoint >}
    285         *             {@link Character#MAX_CODE_POINT}
    286         * @throws IllegalArgumentException
    287         *             if {@code minimumCodePoint < 0}
    288         * @throws IllegalArgumentException
    289         *             if {@code minimumCodePoint > maximumCodePoint}
    290         */
    291        public Builder withinRange(final int minimumCodePoint, final int maximumCodePoint) {
    292            Validate.isTrue(minimumCodePoint <= maximumCodePoint,
    293                    "Minimum code point %d is larger than maximum code point %d", minimumCodePoint, maximumCodePoint);
    294            Validate.isTrue(minimumCodePoint >= 0, "Minimum code point %d is negative", minimumCodePoint);
    295            Validate.isTrue(maximumCodePoint <= Character.MAX_CODE_POINT,
    296                    "Value %d is larger than Character.MAX_CODE_POINT.", maximumCodePoint);
    297            this.minimumCodePoint = minimumCodePoint;
    298            this.maximumCodePoint = maximumCodePoint;
    299            return this;
    300        }
    301    }
    302
    303    /**
    304     * Constructs a new builder.
    305     * @return a new builder.
    306     * @since 1.11.0
    307     */
    308    public static Builder builder() {
    309        return new Builder();
    310    }
    311
    312    /**
    313     * The smallest allowed code point (inclusive).
    314     */
    315    private final int minimumCodePoint;
    316
    317    /**
    318     * The largest allowed code point (inclusive).
    319     */
    320    private final int maximumCodePoint;
    321
    322    /**
    323     * Filters for code points.
    324     */
    325    private final Set<CharacterPredicate> inclusivePredicates;
    326
    327    /**
    328     * The source of randomness for this generator.
    329     */
    330    private final TextRandomProvider random;
    331
    332    /**
    333     * The source of provided characters.
    334     */
    335    private final List<Character> characterList;
    336
    337    /**
    338     * Constructs the generator.
    339     *
    340     * @param minimumCodePoint
    341     *            smallest allowed code point (inclusive)
    342     * @param maximumCodePoint
    343     *            largest allowed code point (inclusive)
    344     * @param inclusivePredicates
    345     *            filters for code points
    346     * @param random
    347     *            source of randomness
    348     * @param characterList list of predefined set of characters.
    349     */
    350    private RandomStringGenerator(final int minimumCodePoint, final int maximumCodePoint,
    351                                  final Set<CharacterPredicate> inclusivePredicates, final TextRandomProvider random,
    352                                  final List<Character> characterList) {
    353        this.minimumCodePoint = minimumCodePoint;
    354        this.maximumCodePoint = maximumCodePoint;
    355        this.inclusivePredicates = inclusivePredicates;
    356        this.random = random;
    357        this.characterList = characterList;
    358    }
    359
    360    /**
    361     * Generates a random string, containing the specified number of code points.
    362     *
    363     * <p>
    364     * Code points are randomly selected between the minimum and maximum values defined
    365     * in the generator.
    366     * Surrogate and private use characters are not returned, although the
    367     * resulting string may contain pairs of surrogates that together encode a
    368     * supplementary character.
    369     * </p>
    370     * <p>
    371     * Note: the number of {@code char} code units generated will exceed
    372     * {@code length} if the string contains supplementary characters. See the
    373     * {@link Character} documentation to understand how Java stores Unicode
    374     * values.
    375     * </p>
    376     *
    377     * @param length
    378     *            the number of code points to generate
    379     * @return The generated string
    380     * @throws IllegalArgumentException
    381     *             if {@code length < 0}
    382     */
    383    public String generate(final int length) {
    384        if (length == 0) {
    385            return StringUtils.EMPTY;
    386        }
    387        Validate.isTrue(length > 0, "Length %d is smaller than zero.", length);
    388        final StringBuilder builder = new StringBuilder(length);
    389        long remaining = length;
    390        do {
    391            final int codePoint;
    392            if (characterList != null && !characterList.isEmpty()) {
    393                codePoint = generateRandomNumber(characterList);
    394            } else {
    395                codePoint = generateRandomNumber(minimumCodePoint, maximumCodePoint);
    396            }
    397            switch (Character.getType(codePoint)) {
    398            case Character.UNASSIGNED:
    399            case Character.PRIVATE_USE:
    400            case Character.SURROGATE:
    401                continue;
    402            default:
    403            }
    404            if (inclusivePredicates != null) {
    405                boolean matchedFilter = false;
    406                for (final CharacterPredicate predicate : inclusivePredicates) {
    407                    if (predicate.test(codePoint)) {
    408                        matchedFilter = true;
    409                        break;
    410                    }
    411                }
    412                if (!matchedFilter) {
    413                    continue;
    414                }
    415            }
    416            builder.appendCodePoint(codePoint);
    417            remaining--;
    418        } while (remaining != 0);
    419        return builder.toString();
    420    }
    421
    422    /**
    423     * Generates a random string, containing between the minimum (inclusive) and the maximum (inclusive)
    424     * number of code points.
    425     *
    426     * @param minLengthInclusive
    427     *            the minimum (inclusive) number of code points to generate
    428     * @param maxLengthInclusive
    429     *            the maximum (inclusive) number of code points to generate
    430     * @return The generated string
    431     * @throws IllegalArgumentException
    432     *             if {@code minLengthInclusive < 0}, or {@code maxLengthInclusive < minLengthInclusive}
    433     * @see RandomStringGenerator#generate(int)
    434     * @since 1.2
    435     */
    436    public String generate(final int minLengthInclusive, final int maxLengthInclusive) {
    437        Validate.isTrue(minLengthInclusive >= 0, "Minimum length %d is smaller than zero.", minLengthInclusive);
    438        Validate.isTrue(minLengthInclusive <= maxLengthInclusive,
    439                "Maximum length %d is smaller than minimum length %d.", maxLengthInclusive, minLengthInclusive);
    440        return generate(generateRandomNumber(minLengthInclusive, maxLengthInclusive));
    441    }
    442
    443    /**
    444     * Generates a random number within a range, using a {@link ThreadLocalRandom} instance
    445     * or the user-supplied source of randomness.
    446     *
    447     * @param minInclusive
    448     *            the minimum value allowed
    449     * @param maxInclusive
    450     *            the maximum value allowed
    451     * @return The random number.
    452     */
    453    private int generateRandomNumber(final int minInclusive, final int maxInclusive) {
    454        if (random != null) {
    455            return random.nextInt(maxInclusive - minInclusive + 1) + minInclusive;
    456        }
    457        return ThreadLocalRandom.current().nextInt(minInclusive, maxInclusive + 1);
    458    }
    459
    460    /**
    461     * Generates a random number within a range, using a {@link ThreadLocalRandom} instance
    462     * or the user-supplied source of randomness.
    463     *
    464     * @param characterList predefined char list.
    465     * @return The random number.
    466     */
    467    private int generateRandomNumber(final List<Character> characterList) {
    468        final int listSize = characterList.size();
    469        if (random != null) {
    470            return String.valueOf(characterList.get(random.nextInt(listSize))).codePointAt(0);
    471        }
    472        return String.valueOf(characterList.get(ThreadLocalRandom.current().nextInt(0, listSize))).codePointAt(0);
    473    }
    474}