[Asp.net core]使用Polly网络请求异常重试

摘要

在网络传输过程当中，不能保证全部的请求都能正确的被服务端接受或者处理，那么进行简单的重试能够进行简单的补救。好比如今大部分支付功能，在支付成功以后，须要回调咱们网站的接口，而且要求咱们的接口给一个相似成功的响应，支付端收到咱们的成功响应，就再也不进行重试请求了。

好比：支付宝文档中有这么一段描述

Polly简单实用

private ILog _log; /// <summary>
        /// 重试时间点 /// </summary>
        private TimeSpan[] _retryTimes = new[] { TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(5), TimeSpan.FromSeconds(10), TimeSpan.FromSeconds(20), TimeSpan.FromMinutes(1) }; /// <summary>
        /// 提交文本 /// </summary>
        /// <param name="url"></param>
        /// <param name="data"></param>
        /// <returns></returns>
        public string PostTxt(string url, Dictionary<string, string> paras) { try { 

 string data = ConvertDic2QueryString(paras); byte[] byteArray = Encoding.UTF8.GetBytes(data);

var retry4TimePolicy = Polly.Policy.Handle<WebException>().WaitAndRetry( _retryTimes, (ex, ts, i, context) => { _log.Info(new LogModel { Content = $"Request:{url},data:{ConvertDic2QueryString(paras)},第{i}次重试", userId= "", Op = "posttxt" }); }); return retry4TimePolicy.Execute(() => {  HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url); request.ContentType = "application/x-www-form-urlencoded"; request.Method = "POST"; request.ContentLength = byteArray.Length; request.Timeout = 60000; if (url.StartsWith("https")) { request.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) => true; } Stream requestStream = request.GetRequestStream(); requestStream.Write(byteArray, 0, byteArray.Length); HttpWebResponse webResponse = (HttpWebResponse)request.GetResponse(); StreamReader reader = new StreamReader(webResponse.GetResponseStream(), Encoding.UTF8); String sResult = reader.ReadToEnd(); requestStream.Close(); reader.Close(); webResponse.Close(); return sResult; }); } catch (WebException ex) { throw ex; } }

public string ConvertDic2QueryString(Dictionary<string, string> dic) { if (dic == null) { return string.Empty; } StringBuilder sb = new StringBuilder(); foreach (var key in dic.Keys) { sb.AppendFormat("{0}={1}&", key, HttpUtility.UrlEncode(dic[key])); } return sb.ToString().TrimEnd('&'); }

能够相似上面的一种请求，在捕获到webException异常时，立马重试一次，检查网络是否正常，若是仍不能正确进行请求，下次5s，10s，20s，进行尝试，若是仍不正常，则在1分钟后进行最后尝试。不然认为网络不正常，则抛出异常，进行日志记录。

 总结

Polly支持多种重试策略，感兴趣的能够移步这里。

http://www.javashuo.com/article/p-opmxxgua-ee.html

http://www.cnblogs.com/xishuai/p/asp-net-core-polly.html