com.diffplug.common.base.MoreCollectors Maven / Gradle / Ivy
/*
* Copyright 2015 DiffPlug
*
* 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
*
* 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 com.diffplug.common.base;
import java.util.Optional;
import java.util.stream.Collector;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;
/** Useful collectors which aren't included as Java 8 built-ins. */
public class MoreCollectors {
/**
* Collector which traverses a stream and returns either a single element
* (if there was only one element) or empty (if there were 0 or more than 1
* elements). It traverses the entire stream, even if two elements
* have been encountered and the empty return value is now certain.
*
* Implementation credit to Misha on StackOverflow.
*/
public static Collector> singleOrEmpty() {
return Collectors.collectingAndThen(Collectors.toList(),
lst -> lst.size() == 1 ? Optional.of(lst.get(0)) : Optional.empty());
}
/**
* Same behavior as {@link #singleOrEmpty}, except that it returns
* early if it is possible to do so. Unfortunately, it is not possible
* to implement early-return behavior using the Collector interface,
* so MoreCollectors takes the stream as an argument.
*
* Implementation credit to Thomas Jungblut on StackOverflow.
*/
public static Optional singleOrEmptyShortCircuiting(Stream stream) {
return stream.limit(2).map(Optional::ofNullable).reduce(Optional.empty(),
(a, b) -> a.isPresent() ^ b.isPresent() ? b : Optional.empty());
}
/**
* Converts a stream of unicode code points into a String.
*
* {@code
* String spacesRemoved = MoreCollectors.codePointsToString("a b c".codePoints().filter(c -> c != ' '));
* Assert.assertEquals("abc", spacesRemoved);;
* }
*
*/
public static String codePointsToString(IntStream codePoints) {
return codePoints.collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append).toString();
}
}