| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.commons.lang3.stream; |
| |
| import java.util.ArrayList; |
| import java.util.Collection; |
| import java.util.Collections; |
| import java.util.List; |
| import java.util.Set; |
| import java.util.function.BiConsumer; |
| import java.util.function.BinaryOperator; |
| import java.util.function.Consumer; |
| import java.util.function.Function; |
| import java.util.function.Predicate; |
| import java.util.function.Supplier; |
| import java.util.stream.Collector; |
| import java.util.stream.Collectors; |
| import java.util.stream.Stream; |
| |
| import org.apache.commons.lang3.ArrayUtils; |
| import org.apache.commons.lang3.function.Failable; |
| import org.apache.commons.lang3.function.FailableConsumer; |
| import org.apache.commons.lang3.function.FailableFunction; |
| import org.apache.commons.lang3.function.FailablePredicate; |
| |
| /** |
| * Provides utility functions, and classes for working with the |
| * {@code java.util.stream} package, or more generally, with Java 8 lambdas. More |
| * specifically, it attempts to address the fact that lambdas are supposed |
| * not to throw Exceptions, at least not checked Exceptions, AKA instances |
| * of {@link Exception}. This enforces the use of constructs like |
| * <pre> |
| * Consumer<java.lang.reflect.Method> consumer = m -> { |
| * try { |
| * m.invoke(o, args); |
| * } catch (Throwable t) { |
| * throw Failable.rethrow(t); |
| * } |
| * }; |
| * stream.forEach(consumer); |
| * </pre> |
| * Using a {@link FailableStream}, this can be rewritten as follows: |
| * <pre> |
| * Streams.failable(stream).forEach((m) -> m.invoke(o, args)); |
| * </pre> |
| * Obviously, the second version is much more concise and the spirit of |
| * Lambda expressions is met better than in the first version. |
| * |
| * @see Stream |
| * @see Failable |
| * @since 3.11 |
| */ |
| public class Streams { |
| |
| /** |
| * A Collector type for arrays. |
| * |
| * @param <O> The array type. |
| */ |
| public static class ArrayCollector<O> implements Collector<O, List<O>, O[]> { |
| private static final Set<Characteristics> characteristics = Collections.emptySet(); |
| private final Class<O> elementType; |
| |
| /** |
| * Constructs a new instance for the given element type. |
| * |
| * @param elementType The element type. |
| */ |
| public ArrayCollector(final Class<O> elementType) { |
| this.elementType = elementType; |
| } |
| |
| @Override |
| public BiConsumer<List<O>, O> accumulator() { |
| return List::add; |
| } |
| |
| @Override |
| public Set<Characteristics> characteristics() { |
| return characteristics; |
| } |
| |
| @Override |
| public BinaryOperator<List<O>> combiner() { |
| return (left, right) -> { |
| left.addAll(right); |
| return left; |
| }; |
| } |
| |
| @Override |
| public Function<List<O>, O[]> finisher() { |
| return list -> list.toArray(ArrayUtils.newInstance(elementType, list.size())); |
| } |
| |
| @Override |
| public Supplier<List<O>> supplier() { |
| return ArrayList::new; |
| } |
| } |
| |
| /** |
| * A reduced, and simplified version of a {@link Stream} with failable method signatures. |
| * |
| * @param <O> The streams element type. |
| */ |
| public static class FailableStream<O extends Object> { |
| |
| private Stream<O> stream; |
| private boolean terminated; |
| |
| /** |
| * Constructs a new instance with the given {@code stream}. |
| * |
| * @param stream The stream. |
| */ |
| public FailableStream(final Stream<O> stream) { |
| this.stream = stream; |
| } |
| |
| /** |
| * Returns whether all elements of this stream match the provided predicate. May not evaluate the predicate on |
| * all elements if not necessary for determining the result. If the stream is empty then {@code true} is |
| * returned and the predicate is not evaluated. |
| * |
| * <p> |
| * This is a short-circuiting terminal operation. |
| * |
| * Note This method evaluates the <em>universal quantification</em> of the predicate over the elements of |
| * the stream (for all x P(x)). If the stream is empty, the quantification is said to be <em>vacuously |
| * satisfied</em> and is always {@code true} (regardless of P(x)). |
| * |
| * @param predicate A non-interfering, stateless predicate to apply to elements of this stream |
| * @return {@code true} If either all elements of the stream match the provided predicate or the stream is |
| * empty, otherwise {@code false}. |
| */ |
| public boolean allMatch(final FailablePredicate<O, ?> predicate) { |
| assertNotTerminated(); |
| return stream().allMatch(Failable.asPredicate(predicate)); |
| } |
| |
| /** |
| * Returns whether any elements of this stream match the provided predicate. May not evaluate the predicate on |
| * all elements if not necessary for determining the result. If the stream is empty then {@code false} is |
| * returned and the predicate is not evaluated. |
| * |
| * <p> |
| * This is a short-circuiting terminal operation. |
| * |
| * Note This method evaluates the <em>existential quantification</em> of the predicate over the elements of |
| * the stream (for some x P(x)). |
| * |
| * @param predicate A non-interfering, stateless predicate to apply to elements of this stream |
| * @return {@code true} if any elements of the stream match the provided predicate, otherwise {@code false} |
| */ |
| public boolean anyMatch(final FailablePredicate<O, ?> predicate) { |
| assertNotTerminated(); |
| return stream().anyMatch(Failable.asPredicate(predicate)); |
| } |
| |
| /** |
| * Throws IllegalStateException if this stream is already terminated. |
| * |
| * @throws IllegalStateException if this stream is already terminated. |
| */ |
| protected void assertNotTerminated() { |
| if (terminated) { |
| throw new IllegalStateException("This stream is already terminated."); |
| } |
| } |
| |
| /** |
| * Performs a mutable reduction operation on the elements of this stream using a {@code Collector}. A |
| * {@code Collector} encapsulates the functions used as arguments to |
| * {@link #collect(Supplier, BiConsumer, BiConsumer)}, allowing for reuse of collection strategies and |
| * composition of collect operations such as multiple-level grouping or partitioning. |
| * |
| * <p> |
| * If the underlying stream is parallel, and the {@code Collector} is concurrent, and either the stream is |
| * unordered or the collector is unordered, then a concurrent reduction will be performed (see {@link Collector} |
| * for details on concurrent reduction.) |
| * |
| * <p> |
| * This is a terminal operation. |
| * |
| * <p> |
| * When executed in parallel, multiple intermediate results may be instantiated, populated, and merged so as to |
| * maintain isolation of mutable data structures. Therefore, even when executed in parallel with non-thread-safe |
| * data structures (such as {@code ArrayList}), no additional synchronization is needed for a parallel |
| * reduction. |
| * |
| * Note The following will accumulate strings into an ArrayList: |
| * |
| * <pre> |
| * {@code |
| * List<String> asList = stringStream.collect(Collectors.toList()); |
| * } |
| * </pre> |
| * |
| * <p> |
| * The following will classify {@code Person} objects by city: |
| * |
| * <pre> |
| * {@code |
| * Map<String, List<Person>> peopleByCity = personStream.collect(Collectors.groupingBy(Person::getCity)); |
| * } |
| * </pre> |
| * |
| * <p> |
| * The following will classify {@code Person} objects by state and city, cascading two {@code Collector}s |
| * together: |
| * |
| * <pre> |
| * {@code |
| * Map<String, Map<String, List<Person>>> peopleByStateAndCity = personStream |
| * .collect(Collectors.groupingBy(Person::getState, Collectors.groupingBy(Person::getCity))); |
| * } |
| * </pre> |
| * |
| * @param <R> the type of the result |
| * @param <A> the intermediate accumulation type of the {@code Collector} |
| * @param collector the {@code Collector} describing the reduction |
| * @return the result of the reduction |
| * @see #collect(Supplier, BiConsumer, BiConsumer) |
| * @see Collectors |
| */ |
| public <A, R> R collect(final Collector<? super O, A, R> collector) { |
| makeTerminated(); |
| return stream().collect(collector); |
| } |
| |
| /** |
| * Performs a mutable reduction operation on the elements of this FailableStream. A mutable reduction is one in |
| * which the reduced value is a mutable result container, such as an {@code ArrayList}, and elements are |
| * incorporated by updating the state of the result rather than by replacing the result. This produces a result |
| * equivalent to: |
| * |
| * <pre> |
| * {@code |
| * R result = supplier.get(); |
| * for (T element : this stream) |
| * accumulator.accept(result, element); |
| * return result; |
| * } |
| * </pre> |
| * |
| * <p> |
| * Like {@link #reduce(Object, BinaryOperator)}, {@code collect} operations can be parallelized without |
| * requiring additional synchronization. |
| * |
| * <p> |
| * This is a terminal operation. |
| * |
| * Note There are many existing classes in the JDK whose signatures are well-suited for use with method |
| * references as arguments to {@code collect()}. For example, the following will accumulate strings into an |
| * {@code ArrayList}: |
| * |
| * <pre> |
| * {@code |
| * List<String> asList = stringStream.collect(ArrayList::new, ArrayList::add, ArrayList::addAll); |
| * } |
| * </pre> |
| * |
| * <p> |
| * The following will take a stream of strings and concatenates them into a single string: |
| * |
| * <pre> |
| * {@code |
| * String concat = stringStream.collect(StringBuilder::new, StringBuilder::append, StringBuilder::append) |
| * .toString(); |
| * } |
| * </pre> |
| * |
| * @param <R> type of the result |
| * @param <A> Type of the accumulator. |
| * @param pupplier a function that creates a new result container. For a parallel execution, this function may |
| * be called multiple times and must return a fresh value each time. |
| * @param accumulator An associative, non-interfering, stateless function for incorporating an additional |
| * element into a result |
| * @param combiner An associative, non-interfering, stateless function for combining two values, which must be |
| * compatible with the accumulator function |
| * @return The result of the reduction |
| */ |
| public <A, R> R collect(final Supplier<R> pupplier, final BiConsumer<R, ? super O> accumulator, |
| final BiConsumer<R, R> combiner) { |
| makeTerminated(); |
| return stream().collect(pupplier, accumulator, combiner); |
| } |
| |
| /** |
| * Returns a FailableStream consisting of the elements of this stream that match the given FailablePredicate. |
| * |
| * <p> |
| * This is an intermediate operation. |
| * |
| * @param predicate a non-interfering, stateless predicate to apply to each element to determine if it should be |
| * included. |
| * @return the new stream |
| */ |
| public FailableStream<O> filter(final FailablePredicate<O, ?> predicate) { |
| assertNotTerminated(); |
| stream = stream.filter(Failable.asPredicate(predicate)); |
| return this; |
| } |
| |
| /** |
| * Performs an action for each element of this stream. |
| * |
| * <p> |
| * This is a terminal operation. |
| * |
| * <p> |
| * The behavior of this operation is explicitly nondeterministic. For parallel stream pipelines, this operation |
| * does <em>not</em> guarantee to respect the encounter order of the stream, as doing so would sacrifice the |
| * benefit of parallelism. For any given element, the action may be performed at whatever time and in whatever |
| * thread the library chooses. If the action accesses shared state, it is responsible for providing the required |
| * synchronization. |
| * |
| * @param action a non-interfering action to perform on the elements |
| */ |
| public void forEach(final FailableConsumer<O, ?> action) { |
| makeTerminated(); |
| stream().forEach(Failable.asConsumer(action)); |
| } |
| |
| /** |
| * Marks this stream as terminated. |
| * |
| * @throws IllegalStateException if this stream is already terminated. |
| */ |
| protected void makeTerminated() { |
| assertNotTerminated(); |
| terminated = true; |
| } |
| |
| /** |
| * Returns a stream consisting of the results of applying the given function to the elements of this stream. |
| * |
| * <p> |
| * This is an intermediate operation. |
| * |
| * @param <R> The element type of the new stream |
| * @param mapper A non-interfering, stateless function to apply to each element |
| * @return the new stream |
| */ |
| public <R> FailableStream<R> map(final FailableFunction<O, R, ?> mapper) { |
| assertNotTerminated(); |
| return new FailableStream<>(stream.map(Failable.asFunction(mapper))); |
| } |
| |
| /** |
| * Performs a reduction on the elements of this stream, using the provided identity value and an associative |
| * accumulation function, and returns the reduced value. This is equivalent to: |
| * |
| * <pre> |
| * {@code |
| * T result = identity; |
| * for (T element : this stream) |
| * result = accumulator.apply(result, element) |
| * return result; |
| * } |
| * </pre> |
| * |
| * but is not constrained to execute sequentially. |
| * |
| * <p> |
| * The {@code identity} value must be an identity for the accumulator function. This means that for all |
| * {@code t}, {@code accumulator.apply(identity, t)} is equal to {@code t}. The {@code accumulator} function |
| * must be an associative function. |
| * |
| * <p> |
| * This is a terminal operation. |
| * |
| * Note Sum, min, max, average, and string concatenation are all special cases of reduction. Summing a |
| * stream of numbers can be expressed as: |
| * |
| * <pre> |
| * {@code |
| * Integer sum = integers.reduce(0, (a, b) -> a + b); |
| * } |
| * </pre> |
| * |
| * or: |
| * |
| * <pre> |
| * {@code |
| * Integer sum = integers.reduce(0, Integer::sum); |
| * } |
| * </pre> |
| * |
| * <p> |
| * While this may seem a more roundabout way to perform an aggregation compared to simply mutating a running |
| * total in a loop, reduction operations parallelize more gracefully, without needing additional synchronization |
| * and with greatly reduced risk of data races. |
| * |
| * @param identity the identity value for the accumulating function |
| * @param accumulator an associative, non-interfering, stateless function for combining two values |
| * @return the result of the reduction |
| */ |
| public O reduce(final O identity, final BinaryOperator<O> accumulator) { |
| makeTerminated(); |
| return stream().reduce(identity, accumulator); |
| } |
| |
| /** |
| * Converts the FailableStream into an equivalent stream. |
| * |
| * @return A stream, which will return the same elements, which this FailableStream would return. |
| */ |
| public Stream<O> stream() { |
| return stream; |
| } |
| } |
| |
| private static <O> Stream<O> nullSafeStream(final Collection<O> collection) { |
| return collection == null ? Stream.empty() : collection.stream(); |
| } |
| |
| /** |
| * Null-safe version of {@link Stream#of(Object[])}. |
| * |
| * @param <T> the type of stream elements. |
| * @param values the elements of the new stream, may be {@code null}. |
| * @return the new stream on {@code values} or {@link Stream#empty()}. |
| * @since 3.13.0 |
| */ |
| @SafeVarargs // Creating a stream from an array is safe |
| public static <T> Stream<T> of(final T... values) { |
| return values == null ? Stream.empty() : Stream.of(values); |
| } |
| |
| /** |
| * Converts the given {@link Collection} into a {@link FailableStream}. This is basically a simplified, reduced |
| * version of the {@link Stream} class, with the same underlying element stream, except that failable objects, like |
| * {@link FailablePredicate}, {@link FailableFunction}, or {@link FailableConsumer} may be applied, instead of |
| * {@link Predicate}, {@link Function}, or {@link Consumer}. The idea is to rewrite a code snippet like this: |
| * |
| * <pre> |
| * final List<O> list; |
| * final Method m; |
| * final Function<O, String> mapper = (o) -> { |
| * try { |
| * return (String) m.invoke(o); |
| * } catch (Throwable t) { |
| * throw Failable.rethrow(t); |
| * } |
| * }; |
| * final List<String> strList = list.stream().map(mapper).collect(Collectors.toList()); |
| * </pre> |
| * |
| * as follows: |
| * |
| * <pre> |
| * final List<O> list; |
| * final Method m; |
| * final List<String> strList = Failable.stream(list.stream()).map((o) -> (String) m.invoke(o)) |
| * .collect(Collectors.toList()); |
| * </pre> |
| * |
| * While the second version may not be <em>quite</em> as efficient (because it depends on the creation of |
| * additional, intermediate objects, of type FailableStream), it is much more concise, and readable, and meets the |
| * spirit of Lambdas better than the first version. |
| * |
| * @param <O> The streams element type. |
| * @param stream The stream, which is being converted. |
| * @return The {@link FailableStream}, which has been created by converting the stream. |
| */ |
| public static <O> FailableStream<O> stream(final Collection<O> stream) { |
| return stream(nullSafeStream(stream)); |
| } |
| |
| /** |
| * Converts the given {@link Stream stream} into a {@link FailableStream}. This is basically a simplified, reduced |
| * version of the {@link Stream} class, with the same underlying element stream, except that failable objects, like |
| * {@link FailablePredicate}, {@link FailableFunction}, or {@link FailableConsumer} may be applied, instead of |
| * {@link Predicate}, {@link Function}, or {@link Consumer}. The idea is to rewrite a code snippet like this: |
| * |
| * <pre> |
| * final List<O> list; |
| * final Method m; |
| * final Function<O, String> mapper = (o) -> { |
| * try { |
| * return (String) m.invoke(o); |
| * } catch (Throwable t) { |
| * throw Failable.rethrow(t); |
| * } |
| * }; |
| * final List<String> strList = list.stream().map(mapper).collect(Collectors.toList()); |
| * </pre> |
| * |
| * as follows: |
| * |
| * <pre> |
| * final List<O> list; |
| * final Method m; |
| * final List<String> strList = Failable.stream(list.stream()).map((o) -> (String) m.invoke(o)) |
| * .collect(Collectors.toList()); |
| * </pre> |
| * |
| * While the second version may not be <em>quite</em> as efficient (because it depends on the creation of |
| * additional, intermediate objects, of type FailableStream), it is much more concise, and readable, and meets the |
| * spirit of Lambdas better than the first version. |
| * |
| * @param <O> The streams element type. |
| * @param stream The stream, which is being converted. |
| * @return The {@link FailableStream}, which has been created by converting the stream. |
| */ |
| public static <O> FailableStream<O> stream(final Stream<O> stream) { |
| return new FailableStream<>(stream); |
| } |
| |
| /** |
| * Returns a {@code Collector} that accumulates the input elements into a new array. |
| * |
| * @param pElementType Type of an element in the array. |
| * @param <O> the type of the input elements |
| * @return a {@code Collector} which collects all the input elements into an array, in encounter order |
| */ |
| public static <O extends Object> Collector<O, ?, O[]> toArray(final Class<O> pElementType) { |
| return new ArrayCollector<>(pElementType); |
| } |
| } |