本文实例讲述了.net文件上传时实现通过文件头确认文件类型的方法，其中 script 用来返回给页面的数据，读者还可以根据自身需要对相关部分自行修改。另外，文件头也可以自行添加定义。

主要代码如下：

AppCode/FileUpload.csusing System;using System.Collections.Generic;using System.IO;using System.Text;using System.Text.RegularExpressions;using System.Web;/// <summary>/// FileHeader 的摘要说明/// </summary>public static class FileUpload{ private static string script = string.Empty; private static bool autonamed = true; private static Random ra = new Random(); public static bool AutoNamed { get { return autonamed; } set { autonamed = value; } } public static string Script { get { return "var upload = [" + script + "];"; } } public static Dictionary<string, byte[]> ImageHeader = new Dictionary<string, byte[]>(); public static Dictionary<string, object> FilesHeader = new Dictionary<string, object>(); static FileUpload() { ImageHeader.Add("gif", new byte[] { 71, 73, 70, 56, 57, 97 }); ImageHeader.Add("bmp", new byte[] { 66, 77 }); ImageHeader.Add("jpg", new byte[] { 255, 216, 255 }); ImageHeader.Add("png", new byte[] { 137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82 }); FilesHeader.Add("pdf", new byte[] { 37, 80, 68, 70, 45, 49, 46, 53 }); FilesHeader.Add("docx", new object[] { new byte[] { 80, 75, 3, 4, 20, 0, 6, 0, 8, 0, 0, 0, 33 }, new Regex(@"word/_rels/document\.xml\.rels", RegexOptions.IgnoreCase) }); FilesHeader.Add("xlsx", new object[] { new byte[] { 80, 75, 3, 4, 20, 0, 6, 0, 8, 0, 0, 0, 33 }, new Regex(@"xl/_rels/workbook\.xml\.rels", RegexOptions.IgnoreCase) }); FilesHeader.Add("pptx", new object[] { new byte[] { 80, 75, 3, 4, 20, 0, 6, 0, 8, 0, 0, 0, 33 }, new Regex(@"ppt/_rels/presentation\.xml\.rels", RegexOptions.IgnoreCase) }); FilesHeader.Add("doc", new object[] { new byte[] { 208, 207, 17, 224, 161, 177, 26, 225 }, new Regex(@"microsoft( office)? word(?![\s\S]*?microsoft)", RegexOptions.IgnoreCase) }); FilesHeader.Add("xls", new object[] { new byte[] { 208, 207, 17, 224, 161, 177, 26, 225 }, new Regex(@"microsoft( office)? excel(?![\s\S]*?microsoft)", RegexOptions.IgnoreCase) }); FilesHeader.Add("ppt", new object[] { new byte[] { 208, 207, 17, 224, 161, 177, 26, 225 }, new Regex(@"c.u.r.r.e.n.t. .u.s.e.r(?![\s\S]*?[a-z])", RegexOptions.IgnoreCase) }); FilesHeader.Add("avi", new byte[] { 65, 86, 73, 32 }); FilesHeader.Add("mpg", new byte[] { 0, 0, 1, 0xBA }); FilesHeader.Add("mpeg", new byte[] { 0, 0, 1, 0xB3 }); FilesHeader.Add("rar", new byte[] { 82, 97, 114, 33, 26, 7 }); FilesHeader.Add("zip", new byte[] { 80, 75, 3, 4 }); } private static string DateTimeStamp() { return DateTime.Now.ToString("yyyyMMddHHmmss") + ra.Next(0, 99999).ToString("00000"); } private static string FileType(Stream str) { string FileExt = string.Empty; foreach (string ext in FilesHeader.Keys) { byte[] header = FilesHeader[ext].GetType() == (new byte[] { }).GetType() ? (byte[])FilesHeader[ext] : (byte[])(((object[])FilesHeader[ext])[0]); byte[] test = new byte[header.Length]; str.Position = 0; str.Read(test, 0, test.Length); bool same = true; for (int i = 0; i < test.Length; i++) { if (test[i] != header[i]) { same = false; break; } } if (FilesHeader[ext].GetType() != (new byte[] { }).GetType() && same) { object[] obj = (object[])FilesHeader[ext]; bool exists = false; if (obj[1].GetType().ToString() == "System.Int32") { for (int ii = 2; ii < obj.Length; ii++) { if (str.Length >= (int)obj[1]) { str.Position = str.Length - (int)obj[1]; byte[] more = (byte[])obj[ii]; byte[] testmore = new byte[more.Length]; str.Read(testmore, 0, testmore.Length); if (Encoding.GetEncoding(936).GetString(more) == Encoding.GetEncoding(936).GetString(testmore)) { exists = true; break; } } } } else if (obj[1].GetType().ToString() == "System.Text.RegularExpressions.Regex") { Regex re = (Regex)obj[1]; str.Position = 0; byte[] buffer = new byte[(int)str.Length]; str.Read(buffer, 0, buffer.Length); string txt = Encoding.ASCII.GetString(buffer); if (re.IsMatch(txt)) { exists = true; } } if (!exists) { same = false; } } if (same) { FileExt = ext; break; } } return FileExt; } private static string ImageType(Stream str) { string FileExt = string.Empty; foreach (string ext in ImageHeader.Keys) { byte[] header = ImageHeader[ext]; byte[] test = new byte[header.Length]; str.Position = 0; str.Read(test, 0, test.Length); bool same = true; for (int i = 0; i < test.Length; i++) { if (test[i] != header[i]) { same = false; break; } } if (same) { FileExt = ext; break; } } if (!string.IsNullOrEmpty(FileExt)) { Encoding[] chkList = new Encoding[] { Encoding.ASCII, Encoding.UTF8, Encoding.GetEncoding(936) }; for (int i = 0; i < chkList.Length; i++) { str.Position = 0; string str_test = new StreamReader(str, chkList[i]).ReadToEnd(); if (Regex.IsMatch(str_test, @"^[^\u0000-\u0008\u000B-\u000C\u000E-\u001F]*$")) { FileExt = string.Empty; break; } } } return FileExt; } private static void CreateFolder(string path) { string t_path = HttpContext.Current.Server.MapPath(path); if (!Directory.Exists(t_path)) { Directory.CreateDirectory(t_path); } } private static string CreateFileName(string name, string ext) { string filename = "/Upload/" + DateTime.Now.ToString("yyyy/MM/dd") + "/" + ext + "/" + (autonamed ? DateTimeStamp() + "." + ext : name); if (File.Exists(HttpContext.Current.Server.MapPath(filename))) { return CreateFileName(name, ext); } else { return filename; } } private static string SaveAs(HttpPostedFile file, string Ext) { string filename = CreateFileName(file.FileName, Ext); CreateFolder(Regex.Match(filename, @"^[\s\S]*?(?=[^\\/]+$)").Value); file.SaveAs(HttpContext.Current.Server.MapPath(filename)); return Regex.Match(HttpContext.Current.Request.Url.ToString(), @"^[\s\S]*?(?=(?<!/)/(?!/))").Value + filename; } private static void SaveInvalid(HttpPostedFile file) { } // 每次提交之前调用此方法，确认返回内容正确 public static void Clear() { script = string.Empty; } public static void Save(HttpPostedFile file) { if (file.ContentLength == 0) { if (file.FileName.Length > 0) { script += (script.Length > 0 ? "," : "") + "{filename:'" + file.FileName + "',upload:false,length:0,target:null,type:''}"; } } else { if (Regex.IsMatch(file.ContentType, @"^image/")) { string ext = ImageType(file.InputStream); if (string.IsNullOrEmpty(ext)) { SaveInvalid(file); script += (script.Length > 0 ? "," : "") + "{filename:'" + file.FileName + "',upload:false,length:" + file.ContentLength + ",target:null,type:''}"; } else { string filename = SaveAs(file, ext); script += (script.Length > 0 ? "," : "") + "{filename:'" + file.FileName + "',upload:true,length:" + file.ContentLength + ",target:'" + filename + "',type:'" + ext + "'}"; } } else if (Regex.IsMatch(file.ContentType, @"^text/")) { } else { string ext = FileType(file.InputStream); if (string.IsNullOrEmpty(ext)) { SaveInvalid(file); script += (script.Length > 0 ? "," : "") + "{filename:'" + file.FileName + "',upload:false,length:" + file.ContentLength + ",target:null,type:'',header:[" + "" + "]}"; } else { string filename = SaveAs(file, ext); script += (script.Length > 0 ? "," : "") + "{filename:'" + file.FileName + "',upload:true,length:" + file.ContentLength + ",target:'" + filename + "',type:'" + ext + "'}"; } } } }}

调用页面：

using System;using System.Web;public partial class _Default : System.Web.UI.Page{ protected void Page_Load(object sender, EventArgs e) { HttpFileCollection files = Request.Files; FileUpload.Clear(); for (int i = 0; i < files.Count; i++) { FileUpload.Save(files[i]); } Response.Write(FileUpload.Script); }}

功能至此完成，读者还可以根据自身需要进一步作出修改与完善。