1.创建字符流：“abcsdnvs”.chars().mapToObj(i -> (char)i)
2.使用收集器将这些字符分组：.collect(Collectors.groupingBy(Function.identity(), LinkedHashMap::new, Collectors.counting()));

    public static void main(String[] args) {
        Map<Character, Long> collect =  "abcsdnvs".chars().mapToObj(i -> (char)i).collect(Collectors.groupingBy(Function.identity(), LinkedHashMap::new, Collectors.counting()));
        collect.forEach( (x,y) -> System.out.println( "Key: " + x + " Val: " + y));

        Optional<Character> firstNonRepeat = collect.entrySet().stream().filter( (e) -> e.getValue() == 1).map(e -> e.getKey()).findFirst();
        if(firstNonRepeat.isPresent()) {
            System.out.println("First non repeating:" + firstNonRepeat.get());
        }
        Optional<Character> firstRepeat = collect.entrySet().stream().filter( (e) -> e.getValue() > 1).map(e -> e.getKey()).findFirst();
        System.out.println("First repeating:" + firstRepeat.orElse(null));

    }