读取yahoo的天气，并下载其中的图片和FLASH到本地

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Net;
using System.IO;
using System.Text.RegularExpressions;
using System.Collections.Generic;
using System.Text;

/**//// <summary>
/// weather 的摘要说明
/// </summary>
public class weather
{
    private string htmlInfo;
    public weather(string city)
    {
        //
        // TODO: 在此处添加构造函数逻辑
        //
        string fileName = DateTime.Now.ToString("yyyyMMdd") + city + ".txt";  //文件名
        string FilePath = System.Web.HttpContext.Current.Server.MapPath(System.Web.HttpContext.Current.Request.ApplicationPath) + "\\images\\";
        fileName = FilePath + fileName;
        string html = "";
        Encoding code = Encoding.GetEncoding("utf-8");
        int start, stop;
        if (!File.Exists(FilePath + fileName))
        {

            WebRequest wreq = WebRequest.Create("http://weather.cn.yahoo.com/weather.html?city=" + city);

            HttpWebResponse wresp = (HttpWebResponse)wreq.GetResponse();
            Stream s = wresp.GetResponseStream();

            StreamReader objreader = new StreamReader(s);

            string sline = "";
            int i = 0;

            while (sline != null)
            {
                i++;
                sline = objreader.ReadLine();
                if (sline != null)
                    html += sline;
            }

            start = html.IndexOf("<!--today -->");
            stop = html.LastIndexOf("<!--//today -->");
            html = html.Substring(start, stop - start);

            html = RequestFileFromHtml(html, "images/", FilePath);

            //保存到Text文件中
            StreamWriter sw = null;
            try
            {
                sw = new StreamWriter(fileName, false, code);
                sw.Write(html);
                sw.Flush();
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                sw.Close();
            }
        }
        else
        {
            //读取文件
            StreamReader sr = null;

            //读取 
            try
            {
                sr = new StreamReader(fileName, code);
                html = sr.ReadToEnd();
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                sr.Close();
            }
        }
        this.htmlInfo = html;
    }

    /**//// <summary>
    /// 读取今天的天气
    /// </summary>
    /// <returns></returns>
    public string getToday()
    {
        string html = this.htmlInfo;
        int start = html.IndexOf("<!--today -->");
        int stop = html.IndexOf("<!--//today -->");
        string html1 = html.Substring(start, stop - start);

        start = html1.IndexOf("<span class=\"ft1\">");
        stop = html1.LastIndexOf("</span>");

        string str = "";
        if (stop > start)
        {
            str = html1.Substring(start, stop - start);
        }

        return str;
    }

    /**//// <summary>
    /// 读取三天的天气
    /// </summary>
    /// <returns></returns>
    public string getThreeDay()
    {
        string html = this.htmlInfo;
        html = html.Replace("<!--//today -->", "&");
        string[] a = html.Split('&');
        string str = "";
        str += "<table width=100% border=0 align=center cellpadding=4 cellspacing=0>";
        str += "<tr>";
        for (int i = 0; i < a.Length; i++)
        {
            if (a[i] != "")
            {
                str += " <td width=33%>" + a[i] + "</td>";
            }
        }
        str += "</tr>";
        str += "</table>";
        return str;
    }

    /**//// <summary>
    /// 下载图片和SWF并修改链接
    /// </summary>
    /// <param name="html">要转换的字符串</param>
    /// <param name="fileUrl">链接</param>
    /// <param name="filePath">保存路径</param>
    /// <returns></returns>
    private string RequestFileFromHtml(string html, string fileUrl, string filePath)
    {
        Uri url;
        string fileName;
        WebClient c = new WebClient();
        string p = @"((http|https|ftp):(\/\/|\\\\){1}(([A-Za-z0-9_-])+[.]){1,}(net|com|cn|org|cc|tv|[0-9]{1,3})(\S*\/)((\S)+[.]{1}(gif|jpg|png|swf)))";
        Regex r = new Regex(p, RegexOptions.Compiled | RegexOptions.IgnoreCase);
        MatchCollection mc = r.Matches(html);

        if (mc.Count > 0)
        {
            List<Uri> urlList = new List<Uri>();
            int matchIndex = 0;

            for (int i = 0; i < mc.Count; i++)
            {
                url = new Uri(mc[i].Value);

                bool repeated = false;
                for (int j = 0; j < urlList.Count; j++)
                {
                    if (url == urlList[j])
                    {
                        repeated = true;
                        break;
                    }
                }

                if (!repeated)
                {
                    urlList.Add(url);
                    matchIndex++;
                }
            }

            for (int i = 0; i < urlList.Count; i++)
            {
                url = urlList[i];
                //fileExt = url.AbsoluteUri.Substring(url.AbsoluteUri.LastIndexOf("."));
                //fileName = string.Format("{0:yyMMddHHmmssff}{1}{2}", DateTime.Now, i, fileExt);
                fileName = url.AbsoluteUri.Substring(url.AbsoluteUri.LastIndexOf("/") + 1);

                html = html.Replace(url.AbsoluteUri, fileUrl + fileName);
                if (!File.Exists(filePath + fileName))
                {
                    try
                    {
                        c.DownloadFile(url, filePath + fileName);
                    }
                    catch
                    {

                    }
                }
            }
        }

        return html;
    } 


}