对于云API服务，常见的方式就是按照API调用次数收费，某些API调用也就有某些限制，比如在特定时间内只允许调用指定的次数以免造成滥用。虽然Autodesk的view and Data API目前还没有应用这样的限制，但我们最好也能实现这样的机制，比如对于或者Access Token这样的操作，一个Access Token是有一定的有效期的，在这个token的有效期内，我们就没必要重复发出API调用获取新的Acces Token，只有返回仍然有效的token就可以了。下面是c#实现的简单的逻辑，用一个全局静态变量来缓存Access Token：
public class Util
{
private static readonly ILog logger = LogManager.GetLogger(typeof(Util));
string baseUrl = "";
RestClient m_client;
public static AccessToken token;
public static DateTime issueDateTime;
//refresh token if the token is about to expire in 5 seconds
public static int ABOUT_EXPIRED_SECONDS = 5;
public Util(string baseUrl)
{
this.baseUrl = baseUrl;
m_client = new RestClient(baseUrl);
}
public AccessToken GetAccessToken(string clientId, string clientSecret)
{
//no token or token is going to be expired
// (less than ABOUT_EXPIRED_SECONDS)
if (token == null
|| (DateTime.Now - issueDateTime).TotalSeconds
> (token.expires_in - ABOUT_EXPIRED_SECONDS))
{
RestRequest req = new RestRequest();
req.Resource = "authentication/v1/authenticate";
req.Method = Method.POST;
req.AddHeader("Content-Type", "application/x-www-form-urlencoded");
req.AddParameter("client_id", clientId);
req.AddParameter("client_secret", clientSecret);
req.AddParameter("grant_type", "client_credentials");
//avoid CORS issue, do not use this if you just need to get access token from same domain
req.AddHeader("Access-Control-Allow-Origin", "*");
IRestResponse<AccessToken> resp = m_client.Execute<AccessToken>(req);
logger.Debug(resp.Content);
if (resp.StatusCode == System.Net.HttpStatusCode.OK)
{
AccessToken ar = resp.Data;
if (ar != null)
{
token = ar;
//update the token issue time
issueDateTime = DateTime.Now;
}
}
else
{
logger.Fatal("Authentication failed! clientId:" + clientId);
}
}
else
{
;//Do nothing, use the saved access token in static var
}
return token;
}
}
当然，根据需要你可以选择其他的方式，比如把token保存在数据库中，或者memcache中。