Java tutorial
/* * 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 org.apache.commons.lang3.Validate; import java.util.ArrayList; import java.util.HashSet; import java.util.List; import java.util.Set; import java.util.Collections; import java.util.concurrent.ThreadLocalRandom; /** * <p> * 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. * </p> * <pre> * // 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); * </pre> * <pre> * // 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); * </pre> * <p> * {@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. * </p> * @since 1.1 */ public final class RandomStringGenerator { /** * 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<CharacterPredicate> inclusivePredicates; /** * The source of randomness for this generator. */ private final TextRandomProvider random; /** * The source of provided characters. */ private final List<Character> 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<CharacterPredicate> inclusivePredicates, final TextRandomProvider random, final List<Character> characterList) { this.minimumCodePoint = minimumCodePoint; this.maximumCodePoint = maximumCodePoint; this.inclusivePredicates = inclusivePredicates; this.random = random; this.characterList = characterList; } /** * 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<Character> 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); } /** * <p> * Generates a random string, containing the specified number of code points. * </p> * <p>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. * </p> * <p> * 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. * </p> * * @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 ""; } Validate.isTrue(length > 0, "Length %d is smaller than zero.", length); final StringBuilder builder = new StringBuilder(length); long remaining = length; do { 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)); } /** * <p>A builder for generating {@code RandomStringGenerator} instances.</p> * <p>The behaviour 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()}.</p> * * <p>All the property setting methods return the {@code Builder} instance to allow for method chaining.</p> * * <p>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.</p> * * <p>The source of randomness can be set using {@link #usingRandom(TextRandomProvider)}, * otherwise {@link ThreadLocalRandom} is used.</p> * * <p>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.</p> * * <p>This class is not thread safe.</p> * @since 1.1 */ public static class Builder implements org.apache.commons.text.Builder<RandomStringGenerator> { /** * 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<CharacterPredicate> inclusivePredicates; /** * The source of randomness. */ private TextRandomProvider random; /** * The source of provided characters. */ private List<Character> characterList; /** * <p> * Specifies the minimum and maximum code points allowed in the * generated string. * </p> * * @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; } /** * <p> * Specifies the array of minimum and maximum char allowed in the * generated string. * </p> * * For example: * <pre> * {@code * char [][] pairs = {{'0','9'}}; * char [][] pairs = {{'a','z'}}; * char [][] pairs = {{'a','z'},{'0','9'}}; * } * </pre> * * @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; } /** * <p> * Limits the characters in the generated string to those that match at * least one of the predicates supplied. * </p> * * <p> * Passing {@code null} or an empty array to this method will revert to the * default behaviour of allowing any character. Multiple calls to this * method will replace the previously stored predicates. * </p> * * @param predicates * the predicates, may be {@code null} or empty * @return {@code this}, to allow method chaining */ public Builder filteredBy(final CharacterPredicate... predicates) { if (predicates == null || predicates.length == 0) { inclusivePredicates = null; return this; } if (inclusivePredicates == null) { inclusivePredicates = new HashSet<>(); } else { inclusivePredicates.clear(); } Collections.addAll(inclusivePredicates, predicates); return this; } /** * <p> * Overrides the default source of randomness. It is highly * recommended that a random number generator library like * <a href="http://commons.apache.org/proper/commons-rng/">Apache Commons RNG</a> * be used to provide the random number generation. * </p> * * <p> * When using Java 8 or later, {@link TextRandomProvider} is a * functional interface and need not be explicitly implemented: * </p> * <pre> * {@code * UniformRandomProvider rng = RandomSource.create(...); * RandomStringGenerator gen = new RandomStringGenerator.Builder() * .usingRandom(rng::nextInt) * // additional builder calls as needed * .build(); * } * </pre> * * <p> * Passing {@code null} to this method will revert to the default source of * randomness. * </p> * * @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; } /** * <p> * Limits the characters in the generated string to those who match at * supplied list of Character. * </p> * * <p> * Passing {@code null} or an empty array to this method will revert to the * default behaviour of allowing any character. Multiple calls to this * method will replace the previously stored Character. * </p> * * @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; } /** * <p>Builds the {@code RandomStringGenerator} using the properties specified.</p> * @return the configured {@code RandomStringGenerator} */ @Override public RandomStringGenerator build() { return new RandomStringGenerator(minimumCodePoint, maximumCodePoint, inclusivePredicates, random, characterList); } } }