.NET Core 实现定时抓取网站文章并发送到邮箱

2020-01-17 22:13:55

字体：大中小

来源：转载

供稿：网友

前言

大家好，我是晓晨。许久没有更新博客了，今天给大家带来一篇干货型文章，一个每隔5分钟抓取博客园首页文章信息并在第二天的上午9点发送到你的邮箱的小工具。比如我在2018年2月14日，9点来到公司我就会收到一封邮件，是2018年2月13日的博客园首页的文章信息。写这个小工具的初衷是，一直有看博客的习惯，但是最近由于各种原因吧，可能几天都不会看一下博客，要是中途错过了什么好文可是十分心疼的哈哈。所以做了个工具，每天归档发到邮箱，妈妈再也不会担心我错过好的文章了。为什么只抓取首页？因为博客园首页文章的质量相对来说高一些。

准备

作为一个持续运行的工具，没有日志记录怎么行，我准备使用的是NLog来记录日志，它有个日志归档功能非常不错。在http请求中，由于网络问题吧可能会出现失败的情况，这里我使用Polly来进行Retry。使用HtmlAgilityPack来解析网页，需要对xpath有一定了解。下面是详细说明：

组件名	用途	github
NLog	记录日志	https://github.com/NLog/NLog
Polly	当http请求失败，进行重试	https://github.com/App-vNext/Polly
HtmlAgilityPack	网页解析	https://github.com/zzzprojects/html-agility-pack
MailKit	发送邮件	https://github.com/jstedfast/MailKit

有不了解的组件，可以通过访问github获取资料。

参考文章

//www.VeVB.COm/article/112595.htm

获取&解析博客园首页数据

我是用的是HttpWebRequest来进行http请求，下面分享一下我简单封装的类库：

using System;using System.IO;using System.Net;using System.Text;namespace CnBlogSubscribeTool{ /// <summary> /// Simple Http Request Class /// .NET Framework >= 4.0 /// Author:stulzq /// CreatedTime:2017-12-12 15:54:47 /// </summary> public class HttpUtil { static HttpUtil() {  //Set connection limit ,Default limit is 2  ServicePointManager.DefaultConnectionLimit = 1024; } /// <summary> /// Default Timeout 20s /// </summary> public static int DefaultTimeout = 20000; /// <summary> /// Is Auto Redirect /// </summary> public static bool DefalutAllowAutoRedirect = true; /// <summary> /// Default Encoding /// </summary> public static Encoding DefaultEncoding = Encoding.UTF8; /// <summary> /// Default UserAgent /// </summary> public static string DefaultUserAgent =  "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.94 Safari/537.36"  ; /// <summary> /// Default Referer /// </summary> public static string DefaultReferer = ""; /// <summary> /// httpget request /// </summary> /// <param name="url">Internet Address</param> /// <returns>string</returns> public static string GetString(string url) {  var stream = GetStream(url);  string result;  using (StreamReader sr = new StreamReader(stream))  {  result = sr.ReadToEnd();  }  return result; } /// <summary> /// httppost request /// </summary> /// <param name="url">Internet Address</param> /// <param name="postData">Post request data</param> /// <returns>string</returns> public static string PostString(string url, string postData) {  var stream = PostStream(url, postData);  string result;  using (StreamReader sr = new StreamReader(stream))  {  result = sr.ReadToEnd();  }  return result; } /// <summary> /// Create Response /// </summary> /// <param name="url"></param> /// <param name="post">Is post Request</param> /// <param name="postData">Post request data</param> /// <returns></returns> public static WebResponse CreateResponse(string url, bool post, string postData = "") {  var httpWebRequest = WebRequest.CreateHttp(url);  httpWebRequest.Timeout = DefaultTimeout;  httpWebRequest.AllowAutoRedirect = DefalutAllowAutoRedirect;  httpWebRequest.UserAgent = DefaultUserAgent;  httpWebRequest.Referer = DefaultReferer;  if (post)  {  var data = DefaultEncoding.GetBytes(postData);  httpWebRequest.Method = "POST";  httpWebRequest.ContentType = "application/x-www-form-urlencoded;charset=utf-8";  httpWebRequest.ContentLength = data.Length;  using (var stream = httpWebRequest.GetRequestStream())  {   stream.Write(data, 0, data.Length);  }  }  try  {  var response = httpWebRequest.GetResponse();  return response;  }  catch (Exception e)  {  throw new Exception(string.Format("Request error,url:{0},IsPost:{1},Data:{2},Message:{3}", url, post, postData, e.Message), e);  } } /// <summary> /// http get request /// </summary> /// <param name="url"></param> /// <returns>Response Stream</returns> public static Stream GetStream(string url) {  var stream = CreateResponse(url, false).GetResponseStream();  if (stream == null)  {  throw new Exception("Response error,the response stream is null");  }  else  {  return stream;  } } /// <summary> /// http post request /// </summary> /// <param name="url"></param> /// <param name="postData">post data</param> /// <returns>Response Stream</returns> public static Stream PostStream(string url, string postData) {  var stream = CreateResponse(url, true, postData).GetResponseStream();  if (stream == null)  {  throw new Exception("Response error,the response stream is null");  }  else  {  return stream;  } } }}

获取首页数据

string res = HttpUtil.GetString(https://www.cnblogs.com);

解析数据

我们成功获取到了html，但是怎么提取我们需要的信息（文章标题、地址、摘要、作者、发布时间）呢。这里就亮出了我们的利剑HtmlAgilityPack，他是一个可以根据xpath来解析网页的组件。

载入我们前面获取的html：

HtmlDocument doc = new HtmlDocument();doc.LoadHtml(html);

从上图中，我们可以看出，每条文章所有信息都在一个class为post_item的div里，我们先获取所有的class=post_item的div

//获取所有文章数据项var itemBodys = doc.DocumentNode.SelectNodes("//div[@class='post_item_body']");

我们继续分析，可以看出文章的标题在class=post_item_body的div下面的h3标签下的a标签，摘要信息在class=post_item_summary的p标签里面，发布时间和作者在class=post_item_foot的div里，分析完毕，我们可以取出我们想要的数据了：

foreach (var itemBody in itemBodys){ //标题元素 var titleElem = itemBody.SelectSingleNode("h3/a"); //获取标题 var title = titleElem?.InnerText; //获取url var url = titleElem?.Attributes["href"]?.Value; //摘要元素 var summaryElem = itemBody.SelectSingleNode("p[@class='post_item_summary']"); //获取摘要 var summary = summaryElem?.InnerText.Replace("/r/n", "").Trim(); //数据项底部元素 var footElem = itemBody.SelectSingleNode("div[@class='post_item_foot']"); //获取作者 var author = footElem?.SelectSingleNode("a")?.InnerText; //获取文章发布时间 var publishTime = Regex.Match(footElem?.InnerText, "//d+-//d+-//d+ //d+://d+").Value; Console.WriteLine($"标题：{title}"); Console.WriteLine($"网址：{url}"); Console.WriteLine($"摘要：{summary}"); Console.WriteLine($"作者：{author}"); Console.WriteLine($"发布时间：{publishTime}"); Console.WriteLine("--------------华丽的分割线---------------");}

运行一下：

我们成功的获取了我们想要的信息。现在我们定义一个Blog对象将它们装起来。

public class Blog{ /// <summary> /// 标题 /// </summary> public string Title { get; set; } /// <summary> /// 博文url /// </summary> public string Url { get; set; } /// <summary> /// 摘要 /// </summary> public string Summary { get; set; } /// <summary> /// 作者 /// </summary> public string Author { get; set; } /// <summary> /// 发布时间 /// </summary> public DateTime PublishTime { get; set; }}

http请求失败重试

我们使用Polly在我们的http请求失败时进行重试，设置为重试3次。

//初始化重试器_retryTwoTimesPolicy = Policy .Handle<Exception>() .Retry(3, (ex, count) => {  _logger.Error("Excuted Failed! Retry {0}", count);  _logger.Error("Exeption from {0}", ex.GetType().Name); });

测试一下：

可以看到当遇到exception是Polly会帮我们重试三次，如果三次重试都失败了那么会放弃。

发送邮件

使用MailKit来进行邮件发送，它支持IMAP，POP3和SMTP协议，并且是跨平台的十分优秀。下面是根据前面园友的分享自己封装的一个类库：

using System.Collections.Generic;using CnBlogSubscribeTool.Config;using MailKit.Net.Smtp;using MimeKit;namespace CnBlogSubscribeTool{ /// <summary> /// send email /// </summary> public class MailUtil { private static bool SendMail(MimeMessage mailMessage,MailConfig config) {  try  {  var smtpClient = new SmtpClient();  smtpClient.Timeout = 10 * 1000; //设置超时时间  smtpClient.Connect(config.Host, config.Port, MailKit.Security.SecureSocketOptions.None);//连接到远程smtp服务器  smtpClient.Authenticate(config.Address, config.Password);  smtpClient.Send(mailMessage);//发送邮件  smtpClient.Disconnect(true);  return true;  }  catch  {  throw;  } } /// <summary> ///发送邮件 /// </summary> /// <param name="config">配置</param> /// <param name="receives">接收人</param> /// <param name="sender">发送人</param> /// <param name="subject">标题</param> /// <param name="body">内容</param> /// <param name="attachments">附件</param> /// <param name="fileName">附件名</param> /// <returns></returns> public static bool SendMail(MailConfig config,List<string> receives, string sender, string subject, string body, byte[] attachments = null,string fileName="") {  var fromMailAddress = new MailboxAddress(config.Name, config.Address);    var mailMessage = new MimeMessage();  mailMessage.From.Add(fromMailAddress);    foreach (var add in receives)  {  var toMailAddress = new MailboxAddress(add);  mailMessage.To.Add(toMailAddress);  }  if (!string.IsNullOrEmpty(sender))  {  var replyTo = new MailboxAddress(config.Name, sender);  mailMessage.ReplyTo.Add(replyTo);  }  var bodyBuilder = new BodyBuilder() { HtmlBody = body };  //附件  if (attachments != null)  {  if (string.IsNullOrEmpty(fileName))  {   fileName = "未命名文件.txt";  }  var attachment = bodyBuilder.Attachments.Add(fileName, attachments);  //解决中文文件名乱码  var charset = "GB18030";  attachment.ContentType.Parameters.Clear();  attachment.ContentDisposition.Parameters.Clear();  attachment.ContentType.Parameters.Add(charset, "name", fileName);  attachment.ContentDisposition.Parameters.Add(charset, "filename", fileName);  //解决文件名不能超过41字符  foreach (var param in attachment.ContentDisposition.Parameters)   param.EncodingMethod = ParameterEncodingMethod.Rfc2047;  foreach (var param in attachment.ContentType.Parameters)   param.EncodingMethod = ParameterEncodingMethod.Rfc2047;  }  mailMessage.Body = bodyBuilder.ToMessageBody();  mailMessage.Subject = subject;  return SendMail(mailMessage, config); } }}

测试一下：