Android按照key的字母给Map排序

/**
     * 按key的英文字母从小到大排列
     *
     * @param map 原来的map
     * @return 排序之后的map
     */
    public static String key_sort(TreeMap map) {
        String key_sort = "";

        TreeMap map2 = new TreeMap(new Comparator() {
            public int compare(String obj1, String obj2) {
                // 降序排序
                return obj2.compareTo(obj1);
            }
        });
        map2 = map;

        Set keySet = map2.keySet();
        Iterator iter = keySet.iterator();
        while (iter.hasNext()) {
            String key = iter.next();
            key_sort = key_sort + key + "=" + map2.get(key) + "&";
        }
        return key_sort.substring(0, key_sort.length() - 1);
    }