vid-app-common/src/main/java/org/onap/vid/utils/Streams.java

   1 package org.onap.vid.utils;
   2
   3 import java.util.Iterator;
   4 import java.util.Spliterator;
   5 import java.util.Spliterators;
   6 import java.util.function.Consumer;
   7 import java.util.function.Predicate;
   8 import java.util.stream.Stream;
   9 import java.util.stream.StreamSupport;
  10
  11 public class Streams {
  12     public static <R> Predicate<R> not(Predicate<R> predicate) {
  13         return predicate.negate();
  14     }
  15
  16     public static <T> Stream<T> fromIterator(final Iterator<T> iterator) {
  17         Iterable<T> iterable = () -> iterator;
  18         return StreamSupport.<T>stream(iterable.spliterator(), false);
  19     }
  20
  21
  22     // https://stackoverflow.com/questions/20746429/limit-a-stream-by-a-predicate
  23     private static <T> Spliterator<T> takeWhile(
  24             Spliterator<T> splitr, Predicate<? super T> predicate) {
  25         return new Spliterators.AbstractSpliterator<T>(splitr.estimateSize(), 0) {
  26             boolean stillGoing = true;
  27             @Override public boolean tryAdvance(Consumer<? super T> consumer) {
  28                 if (stillGoing) {
  29                     boolean hadNext = splitr.tryAdvance(elem -> {
  30                         if (predicate.test(elem)) {
  31                             consumer.accept(elem);
  32                         } else {
  33                             stillGoing = false;
  34                         }
  35                     });
  36                     return hadNext && stillGoing;
  37                 }
  38                 return false;
  39             }
  40         };
  41     }
  42
  43     public static <T> Stream<T> takeWhile(Stream<T> stream, Predicate<? super T> predicate) {
  44         return StreamSupport.stream(takeWhile(stream.spliterator(), predicate), false);
  45     }
  46
  47 }