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/*
* Copyright 2016-2024 the original author or authors.
*
* Licensed 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
*
* https://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.springframework.data.util;
import java.util.Arrays;
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.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 java.util.stream.StreamSupport;
import org.springframework.util.Assert;
/**
* Simple interface to ease streamability of {@link Iterable}s.
*
* @author Oliver Gierke
* @author Christoph Strobl
* @since 2.0
*/
@FunctionalInterface
public interface Streamable extends Iterable, Supplier> {
/**
* Returns an empty {@link Streamable}.
*
* @return will never be {@literal null}.
*/
static Streamable empty() {
return Collections::emptyIterator;
}
/**
* Returns a {@link Streamable} with the given elements.
*
* @param t the elements to return.
* @return
*/
@SafeVarargs
static Streamable of(T... t) {
return () -> Arrays.asList(t).iterator();
}
/**
* Returns a {@link Streamable} for the given {@link Iterable}.
*
* @param iterable must not be {@literal null}.
* @return
*/
static Streamable of(Iterable iterable) {
Assert.notNull(iterable, "Iterable must not be null");
return iterable::iterator;
}
static Streamable of(Supplier> supplier) {
return LazyStreamable.of(supplier);
}
/**
* Creates a non-parallel {@link Stream} of the underlying {@link Iterable}.
*
* @return will never be {@literal null}.
*/
default Stream stream() {
return StreamSupport.stream(spliterator(), false);
}
/**
* Returns a new {@link Streamable} that will apply the given {@link Function} to the current one.
*
* @param mapper must not be {@literal null}.
* @return
* @see Stream#map(Function)
*/
default Streamable map(Function mapper) {
Assert.notNull(mapper, "Mapping function must not be null");
return Streamable.of(() -> stream().map(mapper));
}
/**
* Returns a new {@link Streamable} that will apply the given {@link Function} to the current one.
*
* @param mapper must not be {@literal null}.
* @return
* @see Stream#flatMap(Function)
*/
default Streamable flatMap(Function> mapper) {
Assert.notNull(mapper, "Mapping function must not be null");
return Streamable.of(() -> stream().flatMap(mapper));
}
/**
* Returns a new {@link Streamable} that will apply the given filter {@link Predicate} to the current one.
*
* @param predicate must not be {@literal null}.
* @return
* @see Stream#filter(Predicate)
*/
default Streamable filter(Predicate predicate) {
Assert.notNull(predicate, "Filter predicate must not be null");
return Streamable.of(() -> stream().filter(predicate));
}
/**
* Returns whether the current {@link Streamable} is empty.
*
* @return
*/
default boolean isEmpty() {
return !iterator().hasNext();
}
/**
* Creates a new {@link Streamable} from the current one and the given {@link Stream} concatenated.
*
* @param stream must not be {@literal null}.
* @return
* @since 2.1
*/
default Streamable and(Supplier> stream) {
Assert.notNull(stream, "Stream must not be null");
return Streamable.of(() -> Stream.concat(this.stream(), stream.get()));
}
/**
* Creates a new {@link Streamable} from the current one and the given values concatenated.
*
* @param others must not be {@literal null}.
* @return will never be {@literal null}.
* @since 2.2
*/
@SuppressWarnings("unchecked")
default Streamable and(T... others) {
Assert.notNull(others, "Other values must not be null");
return Streamable.of(() -> Stream.concat(this.stream(), Arrays.stream(others)));
}
/**
* Creates a new {@link Streamable} from the current one and the given {@link Iterable} concatenated.
*
* @param iterable must not be {@literal null}.
* @return will never be {@literal null}.
* @since 2.2
*/
default Streamable and(Iterable iterable) {
Assert.notNull(iterable, "Iterable must not be null");
return Streamable.of(() -> Stream.concat(this.stream(), StreamSupport.stream(iterable.spliterator(), false)));
}
/**
* Convenience method to allow adding a {@link Streamable} directly as otherwise the invocation is ambiguous between
* {@link #and(Iterable)} and {@link #and(Supplier)}.
*
* @param streamable must not be {@literal null}.
* @return will never be {@literal null}.
* @since 2.2
*/
default Streamable and(Streamable streamable) {
return and((Supplier>) streamable);
}
/**
* Creates a new, unmodifiable {@link List}.
*
* @return will never be {@literal null}.
* @since 2.2
*/
default List toList() {
return stream().collect(StreamUtils.toUnmodifiableList());
}
/**
* Creates a new, unmodifiable {@link Set}.
*
* @return will never be {@literal null}.
* @since 2.2
*/
default Set toSet() {
return stream().collect(StreamUtils.toUnmodifiableSet());
}
default Stream get() {
return stream();
}
/**
* A collector to easily produce a {@link Streamable} from a {@link Stream} using {@link Collectors#toList} as
* intermediate collector.
*
* @return
* @see #toStreamable(Collector)
* @since 2.2
*/
public static Collector> toStreamable() {
return toStreamable(Collectors.toList());
}
/**
* A collector to easily produce a {@link Streamable} from a {@link Stream} and the given intermediate collector.
*
* @return
* @since 2.2
*/
@SuppressWarnings("unchecked")
public static > Collector> toStreamable(
Collector intermediate) {
return Collector.of( //
(Supplier) intermediate.supplier(), //
(BiConsumer) intermediate.accumulator(), //
(BinaryOperator) intermediate.combiner(), //
Streamable::of);
}
}