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/*
 * 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;

import java.lang.reflect.Array;
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.Functions.FailableConsumer;
import org.apache.commons.lang3.Functions.FailableFunction;
import org.apache.commons.lang3.Functions.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
 * 
 *     Consumer<java.lang.reflect.Method> consumer = m -> {
 *         try {
 *             m.invoke(o, args);
 *         } catch (Throwable t) {
 *             throw Functions.rethrow(t);
 *         }
 *    };
 *    stream.forEach(consumer);
 * 
* Using a {@link FailableStream}, this can be rewritten as follows: *
 *     Streams.failable(stream).forEach((m) -> m.invoke(o, args));
 * 
* 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 Functions * @since 3.10 * @deprecated Use {@link org.apache.commons.lang3.stream.Streams}. */ @Deprecated public class Streams { /** * A reduced, and simplified version of a {@link Stream} with * failable method signatures. * @param The streams element type. * @deprecated Use {@link org.apache.commons.lang3.stream.Streams.FailableStream}. */ @Deprecated public static class FailableStream { private Stream stream; private boolean terminated; /** * Constructs a new instance with the given {@code stream}. * @param stream The stream. */ public FailableStream(final Stream stream) { this.stream = stream; } protected void assertNotTerminated() { if (terminated) { throw new IllegalStateException("This stream is already terminated."); } } protected void makeTerminated() { assertNotTerminated(); terminated = true; } /** * Returns a FailableStream consisting of the elements of this stream that match * the given FailablePredicate. * *

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 filter(final FailablePredicate predicate){ assertNotTerminated(); stream = stream.filter(Functions.asPredicate(predicate)); return this; } /** * Performs an action for each element of this stream. * *

This is a terminal operation. * *

The behavior of this operation is explicitly nondeterministic. * For parallel stream pipelines, this operation does not * 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 action) { makeTerminated(); stream().forEach(Functions.asConsumer(action)); } /** * 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. * *

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.) * *

This is a terminal operation. * *

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: *

{@code
         *     List asList = stringStream.collect(Collectors.toList());
         * }
* *

The following will classify {@code Person} objects by city: *

{@code
         *     Map> peopleByCity
         *         = personStream.collect(Collectors.groupingBy(Person::getCity));
         * }
* *

The following will classify {@code Person} objects by state and city, * cascading two {@code Collector}s together: *

{@code
         *     Map>> peopleByStateAndCity
         *         = personStream.collect(Collectors.groupingBy(Person::getState,
         *                                                      Collectors.groupingBy(Person::getCity)));
         * }
* * @param the type of the result * @param 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 R collect(final Collector 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: *
{@code
         *     R result = supplier.get();
         *     for (T element : this stream)
         *         accumulator.accept(result, element);
         *     return result;
         * }
* *

Like {@link #reduce(Object, BinaryOperator)}, {@code collect} operations * can be parallelized without requiring additional synchronization. * *

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}: *

{@code
         *     List asList = stringStream.collect(ArrayList::new, ArrayList::add,
         *                                                ArrayList::addAll);
         * }
* *

The following will take a stream of strings and concatenates them into a * single string: *

{@code
         *     String concat = stringStream.collect(StringBuilder::new, StringBuilder::append,
         *                                          StringBuilder::append)
         *                                 .toString();
         * }
* * @param type of the result * @param
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 R collect(final Supplier pupplier, final BiConsumer accumulator, final BiConsumer combiner) { makeTerminated(); return stream().collect(pupplier, accumulator, combiner); } /** * 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: *
{@code
         *     T result = identity;
         *     for (T element : this stream)
         *         result = accumulator.apply(result, element)
         *     return result;
         * }
* * but is not constrained to execute sequentially. * *

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. * *

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: * *

{@code
         *     Integer sum = integers.reduce(0, (a, b) -> a+b);
         * }
* * or: * *
{@code
         *     Integer sum = integers.reduce(0, Integer::sum);
         * }
* *

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 accumulator) { makeTerminated(); return stream().reduce(identity, accumulator); } /** * Returns a stream consisting of the results of applying the given * function to the elements of this stream. * *

This is an intermediate operation. * * @param The element type of the new stream * @param mapper A non-interfering, stateless function to apply to each element * @return the new stream */ public FailableStream map(final FailableFunction mapper) { assertNotTerminated(); return new FailableStream<>(stream.map(Functions.asFunction(mapper))); } /** * Converts the FailableStream into an equivalent stream. * @return A stream, which will return the same elements, which this FailableStream would return. */ public Stream stream() { return 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. * *

This is a short-circuiting terminal operation. * * Note * This method evaluates the universal quantification 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 vacuously * satisfied 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 predicate) { assertNotTerminated(); return stream().allMatch(Functions.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. * *

This is a short-circuiting terminal operation. * * Note * This method evaluates the existential quantification 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 predicate) { assertNotTerminated(); return stream().anyMatch(Functions.asPredicate(predicate)); } } /** * 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: *

     *     final List<O> list;
     *     final Method m;
     *     final Function<O,String> mapper = (o) -> {
     *         try {
     *             return (String) m.invoke(o);
     *         } catch (Throwable t) {
     *             throw Functions.rethrow(t);
     *         }
     *     };
     *     final List<String> strList = list.stream()
     *         .map(mapper).collect(Collectors.toList());
     *  
* as follows: *
     *     final List<O> list;
     *     final Method m;
     *     final List<String> strList = Functions.stream(list.stream())
     *         .map((o) -> (String) m.invoke(o)).collect(Collectors.toList());
     *  
* While the second version may not be quite 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 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 FailableStream stream(final Stream stream) { return new FailableStream<>(stream); } /** * 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: *
     *     final List<O> list;
     *     final Method m;
     *     final Function<O,String> mapper = (o) -> {
     *         try {
     *             return (String) m.invoke(o);
     *         } catch (Throwable t) {
     *             throw Functions.rethrow(t);
     *         }
     *     };
     *     final List<String> strList = list.stream()
     *         .map(mapper).collect(Collectors.toList());
     *  
* as follows: *
     *     final List<O> list;
     *     final Method m;
     *     final List<String> strList = Functions.stream(list.stream())
     *         .map((o) -> (String) m.invoke(o)).collect(Collectors.toList());
     *  
* While the second version may not be quite 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 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 FailableStream stream(final Collection stream) { return stream(stream.stream()); } /** * A Collector type for arrays. * * @param The array type. * @deprecated Use {@link org.apache.commons.lang3.stream.Streams.ArrayCollector}. */ @Deprecated public static class ArrayCollector implements Collector, O[]> { private static final Set characteristics = Collections.emptySet(); private final Class elementType; /** * Constructs a new instance for the given element type. * * @param elementType The element type. */ public ArrayCollector(final Class elementType) { this.elementType = elementType; } @Override public Supplier> supplier() { return ArrayList::new; } @Override public BiConsumer, O> accumulator() { return List::add; } @Override public BinaryOperator> combiner() { return (left, right) -> { left.addAll(right); return left; }; } @Override public Function, O[]> finisher() { return list -> { @SuppressWarnings("unchecked") final O[] array = (O[]) Array.newInstance(elementType, list.size()); return list.toArray(array); }; } @Override public Set characteristics() { return characteristics; } } /** * Returns a {@code Collector} that accumulates the input elements into a * new array. * * @param pElementType Type of an element in the array. * @param the type of the input elements * @return a {@code Collector} which collects all the input elements into an * array, in encounter order */ public static Collector toArray(final Class pElementType) { return new ArrayCollector<>(pElementType); } }




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