Map 转成Json字符串

public class MapUtil {
// map 转成json字符串

    public static String mapToJsonStr(Map map){
        Gson gson = new GsonBuilder().enableComplexMapKeySerialization().create();
        return gson.toJson(map);
    }

// map 转成 key=value & key2=value2形式
    public static String mapToParam(Map<String, Object> map) {
        if (map == null) {
            return "";
        }
        StringBuffer sb = new StringBuffer();
        for (Map.Entry<String, Object> entry : map.entrySet()) {
            sb.append(entry.getKey() + "=" + entry.getValue());
            sb.append("&");
        }
        String s = sb.toString();
        if (s.endsWith("&")) {
            s = org.apache.commons.lang.StringUtils.substringBeforeLast(s, "&");
        }
        return s;
    }

}