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.util.ArrayList;
020import java.util.Collection;
021import java.util.Collections;
022import java.util.List;
023import java.util.Set;
024import java.util.function.BiConsumer;
025import java.util.function.BinaryOperator;
026import java.util.function.Consumer;
027import java.util.function.Function;
028import java.util.function.Predicate;
029import java.util.function.Supplier;
030import java.util.stream.Collector;
031import java.util.stream.Collectors;
032import java.util.stream.Stream;
033
034import org.apache.commons.lang3.Functions.FailableConsumer;
035import org.apache.commons.lang3.Functions.FailableFunction;
036import org.apache.commons.lang3.Functions.FailablePredicate;
037
038/**
039 * Provides utility functions, and classes for working with the
040 * {@code java.util.stream} package, or more generally, with Java 8 lambdas. More
041 * specifically, it attempts to address the fact that lambdas are supposed
042 * not to throw Exceptions, at least not checked Exceptions, AKA instances
043 * of {@link Exception}. This enforces the use of constructs like
044 * <pre>{@code
045 *     Consumer<java.lang.reflect.Method> consumer = m -> {
046 *         try {
047 *             m.invoke(o, args);
048 *         } catch (Throwable t) {
049 *             throw Functions.rethrow(t);
050 *         }
051 *    };
052 *    stream.forEach(consumer);
053 * }</pre>
054 * Using a {@link FailableStream}, this can be rewritten as follows:
055 * <pre>{@code
056 *     Streams.failable(stream).forEach(m -> m.invoke(o, args));
057 * }</pre>
058 * Obviously, the second version is much more concise and the spirit of
059 * Lambda expressions is met better than in the first version.
060 *
061 * @see Stream
062 * @see Functions
063 * @since 3.10
064 * @deprecated Use {@link org.apache.commons.lang3.stream.Streams}.
065 */
066@Deprecated
067public class Streams {
068
069    /**
070     * A Collector type for arrays.
071     *
072     * @param <O> The array type.
073     * @deprecated Use {@link org.apache.commons.lang3.stream.Streams.ArrayCollector}.
074     */
075    @Deprecated
076    public static class ArrayCollector<O> implements Collector<O, List<O>, O[]> {
077        private static final Set<Characteristics> characteristics = Collections.emptySet();
078        private final Class<O> elementType;
079
080        /**
081         * Constructs a new instance for the given element type.
082         *
083         * @param elementType The element type.
084         */
085        public ArrayCollector(final Class<O> elementType) {
086            this.elementType = elementType;
087        }
088
089        @Override
090        public BiConsumer<List<O>, O> accumulator() {
091            return List::add;
092        }
093
094        @Override
095        public Set<Characteristics> characteristics() {
096            return characteristics;
097        }
098
099        @Override
100        public BinaryOperator<List<O>> combiner() {
101            return (left, right) -> {
102                left.addAll(right);
103                return left;
104            };
105        }
106
107        @Override
108        public Function<List<O>, O[]> finisher() {
109            return list -> list.toArray(ArrayUtils.newInstance(elementType, list.size()));
110        }
111
112        @Override
113        public Supplier<List<O>> supplier() {
114            return ArrayList::new;
115        }
116    }
117
118    /**
119     * A reduced, and simplified version of a {@link Stream} with
120     * failable method signatures.
121     * @param <O> The streams element type.
122     * @deprecated Use {@link org.apache.commons.lang3.stream.Streams.FailableStream}.
123     */
124    @Deprecated
125    public static class FailableStream<O> {
126
127        private Stream<O> stream;
128        private boolean terminated;
129
130        /**
131         * Constructs a new instance with the given {@code stream}.
132         * @param stream The stream.
133         */
134        public FailableStream(final Stream<O> stream) {
135            this.stream = stream;
136        }
137
138        /**
139         * Returns whether all elements of this stream match the provided predicate.
140         * May not evaluate the predicate on all elements if not necessary for
141         * determining the result.  If the stream is empty then {@code true} is
142         * returned and the predicate is not evaluated.
143         *
144         * <p>
145         * This is a short-circuiting terminal operation.
146         * </p>
147         *
148         * <p>
149         * Note
150         * This method evaluates the <em>universal quantification</em> of the
151         * predicate over the elements of the stream (for all x P(x)).  If the
152         * stream is empty, the quantification is said to be <em>vacuously
153         * satisfied</em> and is always {@code true} (regardless of P(x)).
154         * </p>
155         *
156         * @param predicate A non-interfering, stateless predicate to apply to
157         * elements of this stream
158         * @return {@code true} If either all elements of the stream match the
159         * provided predicate or the stream is empty, otherwise {@code false}.
160         */
161        public boolean allMatch(final FailablePredicate<O, ?> predicate) {
162            assertNotTerminated();
163            return stream().allMatch(Functions.asPredicate(predicate));
164        }
165
166        /**
167         * Returns whether any elements of this stream match the provided
168         * predicate.  May not evaluate the predicate on all elements if not
169         * necessary for determining the result.  If the stream is empty then
170         * {@code false} is returned and the predicate is not evaluated.
171         *
172         * <p>
173         * This is a short-circuiting terminal operation.
174         * </p>
175         *
176         * Note
177         * This method evaluates the <em>existential quantification</em> of the
178         * predicate over the elements of the stream (for some x P(x)).
179         *
180         * @param predicate A non-interfering, stateless predicate to apply to
181         * elements of this stream
182         * @return {@code true} if any elements of the stream match the provided
183         * predicate, otherwise {@code false}
184         */
185        public boolean anyMatch(final FailablePredicate<O, ?> predicate) {
186            assertNotTerminated();
187            return stream().anyMatch(Functions.asPredicate(predicate));
188        }
189
190        /**
191         * Throws IllegalStateException if this stream is already terminated.
192         *
193         * @throws IllegalStateException if this stream is already terminated.
194         */
195        protected void assertNotTerminated() {
196            if (terminated) {
197                throw new IllegalStateException("This stream is already terminated.");
198            }
199        }
200
201        /**
202         * Performs a mutable reduction operation on the elements of this stream using a
203         * {@link Collector}.  A {@link Collector}
204         * encapsulates the functions used as arguments to
205         * {@link #collect(Supplier, BiConsumer, BiConsumer)}, allowing for reuse of
206         * collection strategies and composition of collect operations such as
207         * multiple-level grouping or partitioning.
208         *
209         * <p>
210         * If the underlying stream is parallel, and the {@link Collector}
211         * is concurrent, and either the stream is unordered or the collector is
212         * unordered, then a concurrent reduction will be performed
213         * (see {@link Collector} for details on concurrent reduction.)
214         * </p>
215         *
216         * <p>
217         * This is an intermediate operation.
218         * </p>
219         *
220         * <p>
221         * When executed in parallel, multiple intermediate results may be
222         * instantiated, populated, and merged so as to maintain isolation of
223         * mutable data structures.  Therefore, even when executed in parallel
224         * with non-thread-safe data structures (such as {@link ArrayList}), no
225         * additional synchronization is needed for a parallel reduction.
226         * </p>
227         * <p>
228         * Note
229         * The following will accumulate strings into an ArrayList:
230         * </p>
231         * <pre>{@code
232         *     List<String> asList = stringStream.collect(Collectors.toList());
233         * }</pre>
234         *
235         * <p>
236         * The following will classify {@code Person} objects by city:
237         * </p>
238         * <pre>{@code
239         *     Map<String, List<Person>> peopleByCity
240         *         = personStream.collect(Collectors.groupingBy(Person::getCity));
241         * }</pre>
242         *
243         * <p>
244         * The following will classify {@code Person} objects by state and city,
245         * cascading two {@link Collector}s together:
246         * </p>
247         * <pre>{@code
248         *     Map<String, Map<String, List<Person>>> peopleByStateAndCity
249         *         = personStream.collect(Collectors.groupingBy(Person::getState,
250         *                                                      Collectors.groupingBy(Person::getCity)));
251         * }</pre>
252         *
253         * @param <R> the type of the result
254         * @param <A> the intermediate accumulation type of the {@link Collector}
255         * @param collector the {@link Collector} describing the reduction
256         * @return the result of the reduction
257         * @see #collect(Supplier, BiConsumer, BiConsumer)
258         * @see Collectors
259         */
260        public <A, R> R collect(final Collector<? super O, A, R> collector) {
261            makeTerminated();
262            return stream().collect(collector);
263        }
264
265        /**
266         * Performs a mutable reduction operation on the elements of this FailableStream.
267         * A mutable reduction is one in which the reduced value is a mutable result
268         * container, such as an {@link ArrayList}, and elements are incorporated by updating
269         * the state of the result rather than by replacing the result. This produces a result equivalent to:
270         * <pre>{@code
271         *     R result = supplier.get();
272         *     for (T element : this stream)
273         *         accumulator.accept(result, element);
274         *     return result;
275         * }</pre>
276         *
277         * <p>
278         * Like {@link #reduce(Object, BinaryOperator)}, {@code collect} operations
279         * can be parallelized without requiring additional synchronization.
280         * </p>
281         *
282         * <p>
283         * This is an intermediate operation.
284         * </p>
285         *
286         * <p>
287         * Note There are many existing classes in the JDK whose signatures are
288         * well-suited for use with method references as arguments to {@code collect()}.
289         * For example, the following will accumulate strings into an {@link ArrayList}:
290         * </p>
291         * <pre>{@code
292         *     List<String> asList = stringStream.collect(ArrayList::new, ArrayList::add,
293         *                                                ArrayList::addAll);
294         * }</pre>
295         *
296         * <p>
297         * The following will take a stream of strings and concatenates them into a
298         * single string:
299         * </p>
300         * <pre>{@code
301         *     String concat = stringStream.collect(StringBuilder::new, StringBuilder::append,
302         *                                          StringBuilder::append)
303         *                                 .toString();
304         * }</pre>
305         *
306         * @param <R> type of the result
307         * @param <A> Type of the accumulator.
308         * @param supplier a function that creates a new result container. For a
309         *                 parallel execution, this function may be called
310         *                 multiple times and must return a fresh value each time.
311         * @param accumulator An associative, non-interfering, stateless function for
312         *   incorporating an additional element into a result
313         * @param combiner An associative, non-interfering, stateless
314         *   function for combining two values, which must be compatible with the
315         *   accumulator function
316         * @return The result of the reduction
317         */
318        public <A, R> R collect(final Supplier<R> supplier, final BiConsumer<R, ? super O> accumulator, final BiConsumer<R, R> combiner) {
319            makeTerminated();
320            return stream().collect(supplier, accumulator, combiner);
321        }
322
323        /**
324         * Returns a FailableStream consisting of the elements of this stream that match
325         * the given FailablePredicate.
326         *
327         * <p>
328         * This is an intermediate operation.
329         * </p>
330         *
331         * @param predicate a non-interfering, stateless predicate to apply to each
332         * element to determine if it should be included.
333         * @return the new stream
334         */
335        public FailableStream<O> filter(final FailablePredicate<O, ?> predicate) {
336            assertNotTerminated();
337            stream = stream.filter(Functions.asPredicate(predicate));
338            return this;
339        }
340
341        /**
342         * Performs an action for each element of this stream.
343         *
344         * <p>
345         * This is an intermediate operation.
346         * </p>
347         *
348         * <p>
349         * The behavior of this operation is explicitly nondeterministic.
350         * For parallel stream pipelines, this operation does <em>not</em>
351         * guarantee to respect the encounter order of the stream, as doing so
352         * would sacrifice the benefit of parallelism.  For any given element, the
353         * action may be performed at whatever time and in whatever thread the
354         * library chooses.  If the action accesses shared state, it is
355         * responsible for providing the required synchronization.
356         * </p>
357         *
358         * @param action a non-interfering action to perform on the elements
359         */
360        public void forEach(final FailableConsumer<O, ?> action) {
361            makeTerminated();
362            stream().forEach(Functions.asConsumer(action));
363        }
364
365        /**
366         * Marks this stream as terminated.
367         *
368         * @throws IllegalStateException if this stream is already terminated.
369         */
370        protected void makeTerminated() {
371            assertNotTerminated();
372            terminated = true;
373        }
374
375        /**
376         * Returns a stream consisting of the results of applying the given
377         * function to the elements of this stream.
378         *
379         * <p>
380         * This is an intermediate operation.
381         * </p>
382         *
383         * @param <R> The element type of the new stream
384         * @param mapper A non-interfering, stateless function to apply to each element
385         * @return the new stream
386         */
387        public <R> FailableStream<R> map(final FailableFunction<O, R, ?> mapper) {
388            assertNotTerminated();
389            return new FailableStream<>(stream.map(Functions.asFunction(mapper)));
390        }
391
392        /**
393         * Performs a reduction on the elements of this stream, using the provided
394         * identity value and an associative accumulation function, and returns
395         * the reduced value.  This is equivalent to:
396         * <pre>{@code
397         *     T result = identity;
398         *     for (T element : this stream)
399         *         result = accumulator.apply(result, element)
400         *     return result;
401         * }</pre>
402         *
403         * but is not constrained to execute sequentially.
404         *
405         * <p>
406         * The {@code identity} value must be an identity for the accumulator
407         * function. This means that for all {@code t},
408         * {@code accumulator.apply(identity, t)} is equal to {@code t}.
409         * The {@code accumulator} function must be an associative function.
410         * </p>
411         *
412         * <p>
413         * This is an intermediate operation.
414         * </p>
415         *
416         * Note Sum, min, max, average, and string concatenation are all special
417         * cases of reduction. Summing a stream of numbers can be expressed as:
418         *
419         * <pre>{@code
420         *     Integer sum = integers.reduce(0, (a, b) -> a+b);
421         * }</pre>
422         *
423         * or:
424         *
425         * <pre>{@code
426         *     Integer sum = integers.reduce(0, Integer::sum);
427         * }</pre>
428         *
429         * <p>
430         * While this may seem a more roundabout way to perform an aggregation
431         * compared to simply mutating a running total in a loop, reduction
432         * operations parallelize more gracefully, without needing additional
433         * synchronization and with greatly reduced risk of data races.
434         * </p>
435         *
436         * @param identity the identity value for the accumulating function
437         * @param accumulator an associative, non-interfering, stateless
438         *                    function for combining two values
439         * @return the result of the reduction
440         */
441        public O reduce(final O identity, final BinaryOperator<O> accumulator) {
442            makeTerminated();
443            return stream().reduce(identity, accumulator);
444        }
445
446        /**
447         * Converts the FailableStream into an equivalent stream.
448         * @return A stream, which will return the same elements, which this FailableStream would return.
449         */
450        public Stream<O> stream() {
451            return stream;
452        }
453    }
454
455    /**
456     * Converts the given {@link Collection} into a {@link FailableStream}.
457     * This is basically a simplified, reduced version of the {@link Stream}
458     * class, with the same underlying element stream, except that failable
459     * objects, like {@link FailablePredicate}, {@link FailableFunction}, or
460     * {@link FailableConsumer} may be applied, instead of
461     * {@link Predicate}, {@link Function}, or {@link Consumer}. The idea is
462     * to rewrite a code snippet like this:
463     * <pre>{@code
464     *     final List<O> list;
465     *     final Method m;
466     *     final Function<O,String> mapper = (o) -> {
467     *         try {
468     *             return (String) m.invoke(o);
469     *         } catch (Throwable t) {
470     *             throw Functions.rethrow(t);
471     *         }
472     *     };
473     *     final List<String> strList = list.stream()
474     *         .map(mapper).collect(Collectors.toList());
475     *  }</pre>
476     *  as follows:
477     *  <pre>{@code
478     *     final List<O> list;
479     *     final Method m;
480     *     final List<String> strList = Functions.stream(list.stream())
481     *         .map((o) -> (String) m.invoke(o)).collect(Collectors.toList());
482     *  }</pre>
483     *  While the second version may not be <em>quite</em> as
484     *  efficient (because it depends on the creation of additional,
485     *  intermediate objects, of type FailableStream), it is much more
486     *  concise, and readable, and meets the spirit of Lambdas better
487     *  than the first version.
488     * @param <O> The streams element type.
489     * @param stream The stream, which is being converted.
490     * @return The {@link FailableStream}, which has been created by
491     *   converting the stream.
492     */
493    public static <O> FailableStream<O> stream(final Collection<O> stream) {
494        return stream(stream.stream());
495    }
496
497    /**
498     * Converts the given {@link Stream stream} into a {@link FailableStream}.
499     * This is basically a simplified, reduced version of the {@link Stream}
500     * class, with the same underlying element stream, except that failable
501     * objects, like {@link FailablePredicate}, {@link FailableFunction}, or
502     * {@link FailableConsumer} may be applied, instead of
503     * {@link Predicate}, {@link Function}, or {@link Consumer}. The idea is
504     * to rewrite a code snippet like this:
505     * <pre>{@code
506     *     final List<O> list;
507     *     final Method m;
508     *     final Function<O,String> mapper = (o) -> {
509     *         try {
510     *             return (String) m.invoke(o);
511     *         } catch (Throwable t) {
512     *             throw Functions.rethrow(t);
513     *         }
514     *     };
515     *     final List<String> strList = list.stream()
516     *         .map(mapper).collect(Collectors.toList());
517     *  }</pre>
518     *  as follows:
519     *  <pre>{@code
520     *     final List<O> list;
521     *     final Method m;
522     *     final List<String> strList = Functions.stream(list.stream())
523     *         .map((o) -> (String) m.invoke(o)).collect(Collectors.toList());
524     *  }</pre>
525     *  While the second version may not be <em>quite</em> as
526     *  efficient (because it depends on the creation of additional,
527     *  intermediate objects, of type FailableStream), it is much more
528     *  concise, and readable, and meets the spirit of Lambdas better
529     *  than the first version.
530     * @param <O> The streams element type.
531     * @param stream The stream, which is being converted.
532     * @return The {@link FailableStream}, which has been created by
533     *   converting the stream.
534     */
535    public static <O> FailableStream<O> stream(final Stream<O> stream) {
536        return new FailableStream<>(stream);
537    }
538
539    /**
540     * Returns a {@link Collector} that accumulates the input elements into a
541     * new array.
542     *
543     * @param pElementType Type of an element in the array.
544     * @param <O> the type of the input elements
545     * @return a {@link Collector} which collects all the input elements into an
546     * array, in encounter order
547     */
548    public static <O> Collector<O, ?, O[]> toArray(final Class<O> pElementType) {
549        return new ArrayCollector<>(pElementType);
550    }
551
552    /**
553     * Constructs a new instance.
554     */
555    public Streams() {
556        // empty
557    }
558}