onap-enabler/onap-enabler-be/src/main/java/org/onap/osam/utils/Streams.java

/*-
 * ============LICENSE_START=======================================================
 * OSAM
 * ================================================================================
 * Copyright (C) 2018 AT&T
 * ================================================================================
 * 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.
 * ============LICENSE_END=========================================================
 */



package org.onap.osam.utils;

import java.util.Iterator;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

public class Streams {
    public static <R> Predicate<R> not(Predicate<R> predicate) {
        return predicate.negate();
    }

    public static <T> Stream<T> fromIterator(final Iterator<T> iterator) {
        Iterable<T> iterable = () -> iterator;
        return StreamSupport.<T>stream(iterable.spliterator(), false);
    }


    // https://stackoverflow.com/questions/20746429/limit-a-stream-by-a-predicate
    private static <T> Spliterator<T> takeWhile(
            Spliterator<T> splitr, Predicate<? super T> predicate) {
        return new Spliterators.AbstractSpliterator<T>(splitr.estimateSize(), 0) {
            boolean stillGoing = true;
            @Override public boolean tryAdvance(Consumer<? super T> consumer) {
                if (stillGoing) {
                    boolean hadNext = splitr.tryAdvance(elem -> {
                        if (predicate.test(elem)) {
                            consumer.accept(elem);
                        } else {
                            stillGoing = false;
                        }
                    });
                    return hadNext && stillGoing;
                }
                return false;
            }
        };
    }

    public static <T> Stream<T> takeWhile(Stream<T> stream, Predicate<? super T> predicate) {
        return StreamSupport.stream(takeWhile(stream.spliterator(), predicate), false);
    }

}