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     * A Collector type for arrays.
444     *
445     * @param <O> The array type.
446     * @deprecated Use {@link org.apache.commons.lang3.stream.Streams.ArrayCollector}.
447     */
448    @Deprecated
449    public static class ArrayCollector<O> implements Collector<O, List<O>, O[]> {
450        private static final Set<Characteristics> characteristics = Collections.emptySet();
451        private final Class<O> elementType;
452
453        /**
454         * Constructs a new instance for the given element type.
455         *
456         * @param elementType The element type.
457         */
458        public ArrayCollector(final Class<O> elementType) {
459            this.elementType = elementType;
460        }
461
462        @Override
463        public Supplier<List<O>> supplier() {
464            return ArrayList::new;
465        }
466
467        @Override
468        public BiConsumer<List<O>, O> accumulator() {
469            return List::add;
470        }
471
472        @Override
473        public BinaryOperator<List<O>> combiner() {
474            return (left, right) -> {
475                left.addAll(right);
476                return left;
477            };
478        }
479
480        @Override
481        public Function<List<O>, O[]> finisher() {
482            return list -> {
483                @SuppressWarnings("unchecked")
484                final O[] array = (O[]) Array.newInstance(elementType, list.size());
485                return list.toArray(array);
486            };
487        }
488
489        @Override
490        public Set<Characteristics> characteristics() {
491            return characteristics;
492        }
493    }
494
495    /**
496     * Returns a {@code Collector} that accumulates the input elements into a
497     * new array.
498     *
499     * @param pElementType Type of an element in the array.
500     * @param <O> the type of the input elements
501     * @return a {@code Collector} which collects all the input elements into an
502     * array, in encounter order
503     */
504    public static <O extends Object> Collector<O, ?, O[]> toArray(final Class<O> pElementType) {
505        return new ArrayCollector<>(pElementType);
506    }
507}