com.foursoft.vecmodel.common.util.StreamUtils Maven / Gradle / Ivy
/*-
* ========================LICENSE_START=================================
* vec-common
* %%
* Copyright (C) 2020 - 2022 4Soft GmbH
* %%
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* of this software and associated documentation files (the "Software"), to deal
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* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* THE SOFTWARE.
* =========================LICENSE_END==================================
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package com.foursoft.vecmodel.common.util;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.*;
import java.util.function.Function;
import java.util.stream.Collector;
import java.util.stream.Stream;
/**
* Utility class that contains helping methods for Streams.
*/
public final class StreamUtils {
private static final Logger LOGGER = LoggerFactory.getLogger(StreamUtils.class);
private StreamUtils() {
// hide default constructor
}
/**
* Removes empty {@link Optional}s from a Stream and unwraps them, when used as a "flatMapper".
*
* @return Unwrapped optional.
* @see Stream#flatMap(Function)
*/
public static Function, Stream> unwrapOptional() {
return o -> o.map(Stream::of)
.orElseGet(Stream::empty);
}
/**
* Returns a function which returns a stream from the given function.
*
* Can be used together with {@link Stream#flatMap(Function)} to cast the stream.
*
* {@code
* List<Person> people = streamOfHouses
* .flatMap(StreamUtils.toStream(House::getPeople))
* .collect(Collectors.toList());
* }
*
*
* @param inputFunction Function to create a Stream.
* @param Input Type of the Function.
* @param Type of the Collection within the given function. Will also determine the type of the Stream.
* @return A stream of the applied Function.
*/
public static Function> toStream(final Function> inputFunction) {
return t -> inputFunction.apply(t)
.stream();
}
/**
* Returns an optional with the first element of a list if available, else an empty optional.
*
* If the list contains more than one element, a debug log entry is fired.
* It also contains the calling stacktrace attached if {@link Logger#isDebugEnabled()} is {@code true}.
*/
public static Collector, Optional> findOneOrNone() {
return Collector.of(ArrayList::new, List::add, (left, right) -> {
left.addAll(right);
return left;
}, list -> {
if (list.isEmpty()) {
return Optional.empty();
}
if (list.size() > 1) {
final String message =
"Did find more than one element in list; will choose first one. All elements: {}";
if (LOGGER.isDebugEnabled()) {
LOGGER.debug(message, list, new IllegalArgumentException("Too many elements found in list."));
} else {
LOGGER.debug(message, list);
}
}
return Optional.ofNullable(list.get(0));
});
}
/**
* Returns the only element in the list. If zero or more than one element is in the list, an exception is thrown.
*/
public static Collector, T> findOne() {
return Collector.of(ArrayList::new, List::add, (left, right) -> {
left.addAll(right);
return left;
}, list -> {
if (list.size() != 1) {
throw new IllegalStateException("Did find zero or more than one element in list: " + list);
}
return list.get(0);
});
}
/**
* Returns a Function which returns a Stream of elements of the given class.
*
* Can be used together with {@link Stream#flatMap(Function)} to filter the stream.
*
* {@code
* List<Developer> developers = streamOfPeople
* .flatMap(StreamUtils.ofClass(Developer.class))
* .collect(Collectors.toList());
* }
*
*
* @param classOfT Class an element must have to stay in the stream.
* @param Input type of the function.
* @param Type of the class which the stream should have.
* @return A stream with the input cast to the given class if applicable.
* If this is not the case, an empty stream will be returned.
*/
public static Function> ofClass(final Class classOfT) {
return t -> {
if (t == null || !classOfT.isAssignableFrom(t.getClass())) {
return Stream.empty();
}
return Stream.of(classOfT.cast(t));
};
}
/**
* Filters a given stream checking if an element is an instance of the given class and casts to it.
*
* @param stream Stream to check and cast to the given class.
* @param clazz Class which should be checked and cast to.
* @param Input type.
* @param Output type.
* @return Stream of the type of the given class.
*/
public static Stream checkAndCast(final Stream stream, final Class clazz) {
return stream
.flatMap(ofClass(clazz));
}
/**
* Streams and filters a given collection checking if an element is an instance of the given class and casts to it.
*
* @param collection Collection to stream, check and cast to the given class.
* @param clazz Class which should be checked and cast to.
* @param Input type.
* @param Output type.
* @return Stream of the type of the given class.
*/
public static Stream checkAndCast(final Collection collection, final Class clazz) {
return checkAndCast(collection.stream(), clazz);
}
/**
* Returns a stream of the given {@link Collection} and removes {@code null} elements from it.
*
* @param collection Collection to stream.
* @param Type of the Collection / Stream.
* @return A Stream of the given Collection without {@code null} elements.
*/
public static Stream nonNullStream(final Collection collection) {
return collection.stream().filter(Objects::nonNull);
}
}