stream流中 filter方法自定义过滤方式

  // 去重
    static <T, R> Predicate<T> distinctByKey(Function<? super T, R> keyExtractor) {
        Map<R, Boolean> seen = new ConcurrentHashMap<>();
        return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
    }
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