java Map按Key排序

public static void main(String[] args) {
        Map<String, String> map = new TreeMap<String, String>();
        map.put("d", "ddddd");
        map.put("c", "ccccc");

        List<Map.Entry<String, String>> list = new ArrayList<Map.Entry<String, String>>(map.entrySet());
        Collections.sort(list, new Comparator<Map.Entry<String, String>>() {
            public int compare(Map.Entry<String, String> o1, Map.Entry<String, String> o2) {
                return o1.getKey().compareTo(o2.getKey());
            }
        });
        String string = String.valueOf(list.get(0)) + String.valueOf(list.get(1));
        System.out.println(string);

    }