简单CACHE机制的实现 using System; using System.Web; using System.Web.Caching; using System.Web.Security; using System.Text; using SnapLibrary; using System.Threading; using System.Drawing; using System.Collections; using System.IO; /**/ /// <summary>

/// 简单CACHE机制的实现

/// </summary> public static class SnapPreviewCache { // 线程超时（毫秒）

static int ThreadTimeOut = 120000; // 页面的超时（毫秒）

static int GetPageTimeOut = 100000; // hashtable，登记每笔的抓取时间

static Hashtable cacheTable = new Hashtable(); static SnapPreviewCache() { } /**/ /// <summary>

/// 简单处理url 到 file的方法，base64编码

/// </summary>

/// <param name="previewUrl"> url </param>

/// <returns> 文件名 </returns> static string adjustPreviewUrl( string previewUrl) { return Convert.ToBase64String(Encoding.GetEncoding("GB2312").GetBytes(previewUrl), Base64FormattingOptions.None); } /**/ /// <summary>

/// 创建一个图象

/// </summary>

/// <param name="previewUrl"> url </param>

/// <returns> 物理文件名 </returns> public static string CreateSnapPreviewFile( string previewUrl) { // STA线程模式

Thread threadProc = new Thread(STAThreadProc); threadProc.SetApartmentState(ApartmentState.STA); // 线程函数参

SnapPreviewFileParam sp = new SnapPreviewFileParam(); sp.Exception = null; sp.File = HttpContext.Current.Request.PhysicalApplicationPath + "Caches\\" + adjustPreviewUrl(previewUrl) + ".jpg"; sp.Url = previewUrl; // 图体积（参考snap.com）

sp.Width = 274; sp.Height = 161; threadProc.Start(sp); try { if (!threadProc.Join(ThreadTimeOut)) { threadProc.Abort(); throw new TimeoutException(); } if (sp.Exception != null) return sp.Exception.Message; } catch { sp.File = HttpContext.Current.Request.PhysicalApplicationPath + "Caches\\loading.gif"; } return sp.File; } /**/ /// <summary>

/// 线程函数

/// </summary>

/// <param name="p"></param> static void STAThreadProc( object p) { SnapPreviewFileParam sp = (p as SnapPreviewFileParam); // 检查是否需要更新

bool update = false; if (cacheTable.ContainsKey(sp.Url)) { DateTime dt = (DateTime)cacheTable[sp.Url]; TimeSpan ts = DateTime.Now - dt; if (ts.TotalDays > 1) update = true; } else { update = true; cacheTable.Add(sp.Url, DateTime.Now); } cacheTable[sp.Url] = DateTime.Now; if (!update && File.Exists(sp.File)) return; // 构造webpage snapshot class

WebPageSnapshot wpsh = new WebPageSnapshot(); wpsh.Width = 300; wpsh.Height = 300; wpsh.Url = sp.Url; wpsh.TimeOut = GetPageTimeOut; Bitmap bmp = new Bitmap(sp.Width, sp.Height); Graphics g = Graphics.FromImage(bmp); try { // 局部复制

g.DrawImage(wpsh.TakeSnapshot(), 0, 0); bmp.Save(sp.File); } catch (Exception ex) { sp.Exception = ex; } finally { g.Dispose(); bmp.Dispose(); } } } /**/ /// <summary>

/// 线程函数参类

/// </summary> class SnapPreviewFileParam { public string File; public string Url; public int Width; public int Height; public Exception Exception; }

protected void Page_Load( object sender, EventArgs e) { /**/ /// 清空缓冲 Response.Clear(); /**/ /// 目标地址 string href = Request["href"]; /**/ /// 调用页域名称 string domain = Request["domain"]; /**/ /// 是否显示空白页 if ( string.IsNullOrEmpty(href) || href.Equals("about:blank", StringComparison.CurrentCultureIgnoreCase)) { Response.TransmitFile( HttpContext.Current.Request.PhysicalApplicationPath + "Caches\\loading.gif" ); return; } /**/ /// 处理url的简单办法 if (href.IndexOf("http://") == -1) if (! string.IsNullOrEmpty(domain)) href = domain.TrimEnd('/') + "/" + href; if (href.IndexOf("http://") == -1) href = "http://" + href; /**/ /// 传送图象 Response.TransmitFile(SnapPreviewCache.CreateSnapPreviewFile(href)); }