java 逗号分割汉字倒叙

public static String pinjie(String str){
        List split = Arrays.asList(str.split(""));
        Collections.reverse(split);
        StringBuilder result = new StringBuilder();
        for (int i = 0; i < split.size()-2; i++) {
            result.append(split.get(i)).append(",");
        }
        result.append(split.get(split.size()-2));
        return result.toString();
    }