code: public GetMaterialListResponse batchGetMaterial(MaterialType type, int offset, int count){
          if(offset < 0) offset = 0;
          if(count > 20) count = 20;
          if(count < 1) count = 1;
  
          GetMaterialListResponse response = null;
          String url = BASE_API_URL + "cgi-bin/material/batchget_material?access_token=#";
          final Map<String, Object> params = new HashMap<String, Object>(4, 1);
          params.put("type", type.toString());
          params.put("offset", offset);
          params.put("count", count);
          BaseResponse r = executePost(url, JSONUtil.toJson(params));
          String resultJson = isSuccess(r.getErrcode()) ? r.getErrmsg() : r.toJsonString();
          response = JSONUtil.toBean(resultJson, GetMaterialListResponse.class);
  
          return response;
      }
docs: 获取素材列表
  @param type 素材类型
  @param offset 从全部素材的该偏移位置开始返回，0表示从第一个素材 返回
  @param count 返回素材的数量，取值在1到20之间
  @return 素材列表结果