List<String> list = Arrays.asList("a","b","c","d");
        System.out.println(list);
        String aa=list.stream().collect(Collectors.joining("、"));
        String bb=String.join("、",list);
        System.out.println(aa);
        System.out.println(bb);

        // String转List
        String[] split = aa.split("、");
        System.out.println(split);
        List<String> strings = Arrays.asList(split);
        System.out.println(strings);