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