/* * 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
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 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 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:
* The following will classify {@code Person} objects by city:
* The following will classify {@code Person} objects by state and city,
* cascading two {@code Collector}s together:
* 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}:
* The following will take a stream of strings and concatenates them into a
* single string:
* 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:
*
* 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 This is an intermediate operation.
*
* @param 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 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{@code
* List
*
* {@code
* Map
*
* {@code
* Map
*
* @param {@code
* R result = supplier.get();
* for (T element : this stream)
* accumulator.accept(result, element);
* return result;
* }
*
* {@code
* List
*
* {@code
* String concat = stringStream.collect(StringBuilder::new, StringBuilder::append,
* StringBuilder::append)
* .toString();
* }
*
* @param {@code
* T result = identity;
* for (T element : this stream)
* result = accumulator.apply(result, element)
* return result;
* }
*
* but is not constrained to execute sequentially.
*
* {@code
* Integer sum = integers.reduce(0, (a, b) -> a+b);
* }
*
* or:
*
* {@code
* Integer sum = integers.reduce(0, Integer::sum);
* }
*
*
* 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
* 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 > 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