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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.stream;

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.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
 * 
 *     Consumer<java.lang.reflect.Method> consumer = m -> {
 *         try {
 *             m.invoke(o, args);
 *         } catch (Throwable t) {
 *             throw Failable.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 Failable * @since 3.11 */ public class Streams { /** * A Collector type for arrays. * * @param The array type. */ 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 BiConsumer, O> accumulator() { return List::add; } @Override public Set characteristics() { return characteristics; } @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 Supplier> supplier() { return ArrayList::new; } } /** * A reduced, and simplified version of a {@link Stream} with failable method signatures. * * @param The streams element type. */ 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; } /** * 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(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. * *

* 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(Failable.asPredicate(predicate)); } 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. * *

* 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); } /** * 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(Failable.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(Failable.asConsumer(action)); } protected void makeTerminated() { assertNotTerminated(); terminated = true; } /** * 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(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: * *

         * {@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); } /** * 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; } } /** * 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 Failable.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 = Failable.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()); } /** * 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 Failable.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 = Failable.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); } /** * 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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