/**

     *

     * @Description: objectid 转换成string 不然就会objectid对象序列化了

     * @param @param obj

     * @param @return

     * @return String

     * @throws

     * @author liangbo

     * @date 2016-5-13

     */

    public static String parseJsonSetId(Object obj) {

        GsonBuilder builder = new GsonBuilder();

        builder.registerTypeAdapter(ObjectId.class,

                new JsonSerializer<ObjectId>() {

                    @Override

                    public JsonElement serialize(ObjectId arg0, Type arg1,

                            JsonSerializationContext arg2) {

                        return new JsonPrimitive(arg0.toString());

                    }

                });

        Gson gson = builder.create();

        return gson.toJson(obj);

    }