    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.lang3;
    018
    019import java.lang.reflect.Array;
    020import java.util.ArrayList;
    021import java.util.Collection;
    022import java.util.Collections;
    023import java.util.List;
    024import java.util.Set;
    025import java.util.function.BiConsumer;
    026import java.util.function.BinaryOperator;
    027import java.util.function.Consumer;
    028import java.util.function.Function;
    029import java.util.function.Predicate;
    030import java.util.function.Supplier;
    031import java.util.stream.Collector;
    032import java.util.stream.Collectors;
    033import java.util.stream.Stream;
    034
    035import org.apache.commons.lang3.Functions.FailableConsumer;
    036import org.apache.commons.lang3.Functions.FailableFunction;
    037import org.apache.commons.lang3.Functions.FailablePredicate;
    038
    039/**
    040 * Provides utility functions, and classes for working with the
    041 * {@code java.util.stream} package, or more generally, with Java 8 lambdas. More
    042 * specifically, it attempts to address the fact that lambdas are supposed
    043 * not to throw Exceptions, at least not checked Exceptions, AKA instances
    044 * of {@link Exception}. This enforces the use of constructs like
    045 * <pre>
    046 *     Consumer&lt;java.lang.reflect.Method&gt; consumer = (m) -&gt; {
    047 *         try {
    048 *             m.invoke(o, args);
    049 *         } catch (Throwable t) {
    050 *             throw Functions.rethrow(t);
    051 *         }
    052 *    };
    053 *    stream.forEach(consumer);
    054 * </pre>
    055 * Using a {@link FailableStream}, this can be rewritten as follows:
    056 * <pre>
    057 *     Streams.failable(stream).forEach((m) -&gt; m.invoke(o, args));
    058 * </pre>
    059 * Obviously, the second version is much more concise and the spirit of
    060 * Lambda expressions is met better than in the first version.
    061 *
    062 * @see Stream
    063 * @see Functions
    064 * @since 3.10
    065 * @deprecated Use {@link org.apache.commons.lang3.stream.Streams}.
    066 */
    067@Deprecated
    068public class Streams {
    069
    070   /**
    071    * A reduced, and simplified version of a {@link Stream} with
    072    * failable method signatures.
    073    * @param <O> The streams element type.
    074    * @deprecated Use {@link org.apache.commons.lang3.stream.Streams.FailableStream}.
    075    */
    076    @Deprecated
    077    public static class FailableStream<O extends Object> {
    078
    079        private Stream<O> stream;
    080        private boolean terminated;
    081
    082        /**
    083         * Constructs a new instance with the given {@code stream}.
    084         * @param stream The stream.
    085         */
    086        public FailableStream(final Stream<O> stream) {
    087            this.stream = stream;
    088        }
    089
    090        protected void assertNotTerminated() {
    091            if (terminated) {
    092                throw new IllegalStateException("This stream is already terminated.");
    093            }
    094        }
    095
    096        protected void makeTerminated() {
    097            assertNotTerminated();
    098            terminated = true;
    099        }
    100
    101        /**
    102         * Returns a FailableStream consisting of the elements of this stream that match
    103         * the given FailablePredicate.
    104         *
    105         * <p>This is an intermediate operation.
    106         *
    107         * @param predicate a non-interfering, stateless predicate to apply to each
    108         * element to determine if it should be included.
    109         * @return the new stream
    110         */
    111        public FailableStream<O> filter(final FailablePredicate<O, ?> predicate){
    112            assertNotTerminated();
    113            stream = stream.filter(Functions.asPredicate(predicate));
    114            return this;
    115        }
    116
    117        /**
    118         * Performs an action for each element of this stream.
    119         *
    120         * <p>This is a terminal operation.
    121         *
    122         * <p>The behavior of this operation is explicitly nondeterministic.
    123         * For parallel stream pipelines, this operation does <em>not</em>
    124         * guarantee to respect the encounter order of the stream, as doing so
    125         * would sacrifice the benefit of parallelism.  For any given element, the
    126         * action may be performed at whatever time and in whatever thread the
    127         * library chooses.  If the action accesses shared state, it is
    128         * responsible for providing the required synchronization.
    129         *
    130         * @param action a non-interfering action to perform on the elements
    131         */
    132        public void forEach(final FailableConsumer<O, ?> action) {
    133            makeTerminated();
    134            stream().forEach(Functions.asConsumer(action));
    135        }
    136
    137        /**
    138         * Performs a mutable reduction operation on the elements of this stream using a
    139         * {@code Collector}.  A {@code Collector}
    140         * encapsulates the functions used as arguments to
    141         * {@link #collect(Supplier, BiConsumer, BiConsumer)}, allowing for reuse of
    142         * collection strategies and composition of collect operations such as
    143         * multiple-level grouping or partitioning.
    144         *
    145         * <p>If the underlying stream is parallel, and the {@code Collector}
    146         * is concurrent, and either the stream is unordered or the collector is
    147         * unordered, then a concurrent reduction will be performed
    148         * (see {@link Collector} for details on concurrent reduction.)
    149         *
    150         * <p>This is a terminal operation.
    151         *
    152         * <p>When executed in parallel, multiple intermediate results may be
    153         * instantiated, populated, and merged so as to maintain isolation of
    154         * mutable data structures.  Therefore, even when executed in parallel
    155         * with non-thread-safe data structures (such as {@code ArrayList}), no
    156         * additional synchronization is needed for a parallel reduction.
    157         *
    158         * Note
    159         * The following will accumulate strings into an ArrayList:
    160         * <pre>{@code
    161         *     List<String> asList = stringStream.collect(Collectors.toList());
    162         * }</pre>
    163         *
    164         * <p>The following will classify {@code Person} objects by city:
    165         * <pre>{@code
    166         *     Map<String, List<Person>> peopleByCity
    167         *         = personStream.collect(Collectors.groupingBy(Person::getCity));
    168         * }</pre>
    169         *
    170         * <p>The following will classify {@code Person} objects by state and city,
    171         * cascading two {@code Collector}s together:
    172         * <pre>{@code
    173         *     Map<String, Map<String, List<Person>>> peopleByStateAndCity
    174         *         = personStream.collect(Collectors.groupingBy(Person::getState,
    175         *                                                      Collectors.groupingBy(Person::getCity)));
    176         * }</pre>
    177         *
    178         * @param <R> the type of the result
    179         * @param <A> the intermediate accumulation type of the {@code Collector}
    180         * @param collector the {@code Collector} describing the reduction
    181         * @return the result of the reduction
    182         * @see #collect(Supplier, BiConsumer, BiConsumer)
    183         * @see Collectors
    184         */
    185        public <A, R> R collect(final Collector<? super O, A, R> collector) {
    186            makeTerminated();
    187            return stream().collect(collector);
    188        }
    189
    190        /**
    191         * Performs a mutable reduction operation on the elements of this FailableStream.
    192         * A mutable reduction is one in which the reduced value is a mutable result
    193         * container, such as an {@code ArrayList}, and elements are incorporated by updating
    194         * the state of the result rather than by replacing the result. This produces a result equivalent to:
    195         * <pre>{@code
    196         *     R result = supplier.get();
    197         *     for (T element : this stream)
    198         *         accumulator.accept(result, element);
    199         *     return result;
    200         * }</pre>
    201         *
    202         * <p>Like {@link #reduce(Object, BinaryOperator)}, {@code collect} operations
    203         * can be parallelized without requiring additional synchronization.
    204         *
    205         * <p>This is a terminal operation.
    206         *
    207         * Note There are many existing classes in the JDK whose signatures are
    208         * well-suited for use with method references as arguments to {@code collect()}.
    209         * For example, the following will accumulate strings into an {@code ArrayList}:
    210         * <pre>{@code
    211         *     List<String> asList = stringStream.collect(ArrayList::new, ArrayList::add,
    212         *                                                ArrayList::addAll);
    213         * }</pre>
    214         *
    215         * <p>The following will take a stream of strings and concatenates them into a
    216         * single string:
    217         * <pre>{@code
    218         *     String concat = stringStream.collect(StringBuilder::new, StringBuilder::append,
    219         *                                          StringBuilder::append)
    220         *                                 .toString();
    221         * }</pre>
    222         *
    223         * @param <R> type of the result
    224         * @param <A> Type of the accumulator.
    225         * @param pupplier a function that creates a new result container. For a
    226         *                 parallel execution, this function may be called
    227         *                 multiple times and must return a fresh value each time.
    228         * @param accumulator An associative, non-interfering, stateless function for
    229         *   incorporating an additional element into a result
    230         * @param combiner An associative, non-interfering, stateless
    231         *   function for combining two values, which must be compatible with the
    232         *   accumulator function
    233         * @return The result of the reduction
    234         */
    235        public <A, R> R collect(final Supplier<R> pupplier, final BiConsumer<R, ? super O> accumulator, final BiConsumer<R, R> combiner) {
    236            makeTerminated();
    237            return stream().collect(pupplier, accumulator, combiner);
    238        }
    239
    240        /**
    241         * Performs a reduction on the elements of this stream, using the provided
    242         * identity value and an associative accumulation function, and returns
    243         * the reduced value.  This is equivalent to:
    244         * <pre>{@code
    245         *     T result = identity;
    246         *     for (T element : this stream)
    247         *         result = accumulator.apply(result, element)
    248         *     return result;
    249         * }</pre>
    250         *
    251         * but is not constrained to execute sequentially.
    252         *
    253         * <p>The {@code identity} value must be an identity for the accumulator
    254         * function. This means that for all {@code t},
    255         * {@code accumulator.apply(identity, t)} is equal to {@code t}.
    256         * The {@code accumulator} function must be an associative function.
    257         *
    258         * <p>This is a terminal operation.
    259         *
    260         * Note Sum, min, max, average, and string concatenation are all special
    261         * cases of reduction. Summing a stream of numbers can be expressed as:
    262         *
    263         * <pre>{@code
    264         *     Integer sum = integers.reduce(0, (a, b) -> a+b);
    265         * }</pre>
    266         *
    267         * or:
    268         *
    269         * <pre>{@code
    270         *     Integer sum = integers.reduce(0, Integer::sum);
    271         * }</pre>
    272         *
    273         * <p>While this may seem a more roundabout way to perform an aggregation
    274         * compared to simply mutating a running total in a loop, reduction
    275         * operations parallelize more gracefully, without needing additional
    276         * synchronization and with greatly reduced risk of data races.
    277         *
    278         * @param identity the identity value for the accumulating function
    279         * @param accumulator an associative, non-interfering, stateless
    280         *                    function for combining two values
    281         * @return the result of the reduction
    282         */
    283        public O reduce(final O identity, final BinaryOperator<O> accumulator) {
    284            makeTerminated();
    285            return stream().reduce(identity, accumulator);
    286        }
    287
    288        /**
    289         * Returns a stream consisting of the results of applying the given
    290         * function to the elements of this stream.
    291         *
    292         * <p>This is an intermediate operation.
    293         *
    294         * @param <R> The element type of the new stream
    295         * @param mapper A non-interfering, stateless function to apply to each element
    296         * @return the new stream
    297         */
    298        public <R> FailableStream<R> map(final FailableFunction<O, R, ?> mapper) {
    299            assertNotTerminated();
    300            return new FailableStream<>(stream.map(Functions.asFunction(mapper)));
    301        }
    302
    303        /**
    304         * Converts the FailableStream into an equivalent stream.
    305         * @return A stream, which will return the same elements, which this FailableStream would return.
    306         */
    307        public Stream<O> stream() {
    308            return stream;
    309        }
    310
    311        /**
    312         * Returns whether all elements of this stream match the provided predicate.
    313         * May not evaluate the predicate on all elements if not necessary for
    314         * determining the result.  If the stream is empty then {@code true} is
    315         * returned and the predicate is not evaluated.
    316         *
    317         * <p>This is a short-circuiting terminal operation.
    318         *
    319         * Note
    320         * This method evaluates the <em>universal quantification</em> of the
    321         * predicate over the elements of the stream (for all x P(x)).  If the
    322         * stream is empty, the quantification is said to be <em>vacuously
    323         * satisfied</em> and is always {@code true} (regardless of P(x)).
    324         *
    325         * @param predicate A non-interfering, stateless predicate to apply to
    326         * elements of this stream
    327         * @return {@code true} If either all elements of the stream match the
    328         * provided predicate or the stream is empty, otherwise {@code false}.
    329         */
    330        public boolean allMatch(final FailablePredicate<O, ?> predicate) {
    331            assertNotTerminated();
    332            return stream().allMatch(Functions.asPredicate(predicate));
    333        }
    334
    335        /**
    336         * Returns whether any elements of this stream match the provided
    337         * predicate.  May not evaluate the predicate on all elements if not
    338         * necessary for determining the result.  If the stream is empty then
    339         * {@code false} is returned and the predicate is not evaluated.
    340         *
    341         * <p>This is a short-circuiting terminal operation.
    342         *
    343         * Note
    344         * This method evaluates the <em>existential quantification</em> of the
    345         * predicate over the elements of the stream (for some x P(x)).
    346         *
    347         * @param predicate A non-interfering, stateless predicate to apply to
    348         * elements of this stream
    349         * @return {@code true} if any elements of the stream match the provided
    350         * predicate, otherwise {@code false}
    351         */
    352        public boolean anyMatch(final FailablePredicate<O, ?> predicate) {
    353            assertNotTerminated();
    354            return stream().anyMatch(Functions.asPredicate(predicate));
    355        }
    356    }
    357
    358    /**
    359     * Converts the given {@link Stream stream} into a {@link FailableStream}.
    360     * This is basically a simplified, reduced version of the {@link Stream}
    361     * class, with the same underlying element stream, except that failable
    362     * objects, like {@link FailablePredicate}, {@link FailableFunction}, or
    363     * {@link FailableConsumer} may be applied, instead of
    364     * {@link Predicate}, {@link Function}, or {@link Consumer}. The idea is
    365     * to rewrite a code snippet like this:
    366     * <pre>
    367     *     final List&lt;O&gt; list;
    368     *     final Method m;
    369     *     final Function&lt;O,String&gt; mapper = (o) -&gt; {
    370     *         try {
    371     *             return (String) m.invoke(o);
    372     *         } catch (Throwable t) {
    373     *             throw Functions.rethrow(t);
    374     *         }
    375     *     };
    376     *     final List&lt;String&gt; strList = list.stream()
    377     *         .map(mapper).collect(Collectors.toList());
    378     *  </pre>
    379     *  as follows:
    380     *  <pre>
    381     *     final List&lt;O&gt; list;
    382     *     final Method m;
    383     *     final List&lt;String&gt; strList = Functions.stream(list.stream())
    384     *         .map((o) -&gt; (String) m.invoke(o)).collect(Collectors.toList());
    385     *  </pre>
    386     *  While the second version may not be <em>quite</em> as
    387     *  efficient (because it depends on the creation of additional,
    388     *  intermediate objects, of type FailableStream), it is much more
    389     *  concise, and readable, and meets the spirit of Lambdas better
    390     *  than the first version.
    391     * @param <O> The streams element type.
    392     * @param stream The stream, which is being converted.
    393     * @return The {@link FailableStream}, which has been created by
    394     *   converting the stream.
    395     */
    396    public static <O> FailableStream<O> stream(final Stream<O> stream) {
    397        return new FailableStream<>(stream);
    398    }
    399
    400    /**
    401     * Converts the given {@link Collection} into a {@link FailableStream}.
    402     * This is basically a simplified, reduced version of the {@link Stream}
    403     * class, with the same underlying element stream, except that failable
    404     * objects, like {@link FailablePredicate}, {@link FailableFunction}, or
    405     * {@link FailableConsumer} may be applied, instead of
    406     * {@link Predicate}, {@link Function}, or {@link Consumer}. The idea is
    407     * to rewrite a code snippet like this:
    408     * <pre>
    409     *     final List&lt;O&gt; list;
    410     *     final Method m;
    411     *     final Function&lt;O,String&gt; mapper = (o) -&gt; {
    412     *         try {
    413     *             return (String) m.invoke(o);
    414     *         } catch (Throwable t) {
    415     *             throw Functions.rethrow(t);
    416     *         }
    417     *     };
    418     *     final List&lt;String&gt; strList = list.stream()
    419     *         .map(mapper).collect(Collectors.toList());
    420     *  </pre>
    421     *  as follows:
    422     *  <pre>
    423     *     final List&lt;O&gt; list;
    424     *     final Method m;
    425     *     final List&lt;String&gt; strList = Functions.stream(list.stream())
    426     *         .map((o) -&gt; (String) m.invoke(o)).collect(Collectors.toList());
    427     *  </pre>
    428     *  While the second version may not be <em>quite</em> as
    429     *  efficient (because it depends on the creation of additional,
    430     *  intermediate objects, of type FailableStream), it is much more
    431     *  concise, and readable, and meets the spirit of Lambdas better
    432     *  than the first version.
    433     * @param <O> The streams element type.
    434     * @param stream The stream, which is being converted.
    435     * @return The {@link FailableStream}, which has been created by
    436     *   converting the stream.
    437     */
    438    public static <O> FailableStream<O> stream(final Collection<O> stream) {
    439        return stream(stream.stream());
    440    }
    441
    442    /**
    443     * @deprecated Use {@link org.apache.commons.lang3.stream.Streams.ArrayCollector}.
    444     */
    445    @Deprecated
    446    public static class ArrayCollector<O> implements Collector<O, List<O>, O[]> {
    447        private static final Set<Characteristics> characteristics = Collections.emptySet();
    448        private final Class<O> elementType;
    449
    450        public ArrayCollector(final Class<O> elementType) {
    451            this.elementType = elementType;
    452        }
    453
    454        @Override
    455        public Supplier<List<O>> supplier() {
    456            return ArrayList::new;
    457        }
    458
    459        @Override
    460        public BiConsumer<List<O>, O> accumulator() {
    461            return List::add;
    462        }
    463
    464        @Override
    465        public BinaryOperator<List<O>> combiner() {
    466            return (left, right) -> {
    467                left.addAll(right);
    468                return left;
    469            };
    470        }
    471
    472        @Override
    473        public Function<List<O>, O[]> finisher() {
    474            return list -> {
    475                @SuppressWarnings("unchecked")
    476                final O[] array = (O[]) Array.newInstance(elementType, list.size());
    477                return list.toArray(array);
    478            };
    479        }
    480
    481        @Override
    482        public Set<Characteristics> characteristics() {
    483            return characteristics;
    484        }
    485    }
    486
    487    /**
    488     * Returns a {@code Collector} that accumulates the input elements into a
    489     * new array.
    490     *
    491     * @param pElementType Type of an element in the array.
    492     * @param <O> the type of the input elements
    493     * @return a {@code Collector} which collects all the input elements into an
    494     * array, in encounter order
    495     */
    496    public static <O extends Object> Collector<O, ?, O[]> toArray(final Class<O> pElementType) {
    497        return new ArrayCollector<>(pElementType);
    498    }
    499}