【stream】處理含null欄位的排序
阿新 • • 發佈:2018-12-10
msgInfoList=msgInfoList.stream().sorted(Comparator.comparing(l->l.getCreateDate(), Comparator.nullsFirst(java.util.Date::compareTo).reversed())).collect(Collectors.toList());
原始碼:
public static <T, U> Comparator<T> comparing( Function<? super T, ? extends U> keyExtractor, Comparator<? super U> keyComparator) { Objects.requireNonNull(keyExtractor); Objects.requireNonNull(keyComparator); return (Comparator<T> & Serializable) (c1, c2) -> keyComparator.compare(keyExtractor.apply(c1), keyExtractor.apply(c2)); } public static <T> Comparator<T> nullsFirst(Comparator<? super T> comparator) { return new Comparators.NullComparator<>(true, comparator); } final static class NullComparator<T> implements Comparator<T>, Serializable { private static final long serialVersionUID = -7569533591570686392L; private final boolean nullFirst; // if null, non-null Ts are considered equal private final Comparator<T> real; @SuppressWarnings("unchecked") NullComparator(boolean nullFirst, Comparator<? super T> real) { this.nullFirst = nullFirst; this.real = (Comparator<T>) real; } @Override public int compare(T a, T b) { if (a == null) { return (b == null) ? 0 : (nullFirst ? -1 : 1); } else if (b == null) { return nullFirst ? 1: -1; } else { return (real == null) ? 0 : real.compare(a, b); } } @Override public Comparator<T> thenComparing(Comparator<? super T> other) { Objects.requireNonNull(other); return new NullComparator<>(nullFirst, real == null ? other : real.thenComparing(other)); } @Override public Comparator<T> reversed() { return new NullComparator<>(!nullFirst, real == null ? null : real.reversed()); } }