ASP.net判断上传文件类型的三种方法

Boolean fileOk = false;          string path = Server.MapPath("~/images/");          //判断是否已经选取文件          if (FileUpload1.HasFile)          {              //取得文件的扩展名,并转换成小写              string fileExtension = System.IO.Path.GetExtension(FileUpload1.FileName).ToLower();              //限定只能上传jpg和gif图片              string[] allowExtension = { ".jpg", ".gif" };              //对上传的文件的类型进行一个个匹对              int j = 0;              for (int i = 0; i < allowExtension.Length; i++)              {                  if (fileExtension == allowExtension[i])                  {                      fileOk = true;                      return;                  }                  else                  {                      j++;                  }              }              if (j > 0)              {                  Response.Write("<script>alert('文件格式不正确');</script>");                  return;              }          }          else          {              Response.Write("<script>alert('你还没有选择文件');</script>");              return;          }          //如果扩展名符合条件，则上传          if (fileOk)          {              FileUpload1.PostedFile.SaveAs(path + FileUpload1.FileName);              Response.Write("<script>alert('上传成功');</script>");          }

Boolean fileOk = false;           string path = Server.MapPath("~/images/");           //判断是否已经选取文件           if (FileUpload1.HasFile)           {               //取得文件MIME内容类型               string type = this.FileUpload1.PostedFile.ContentType.ToLower();               if (type.Contains("image"))    //图片的MIME类型为"image/xxx"，这里只判断是否图片。               {                   fileOk = true;                }               else               {                   Response.Write("<script>alert('格式不正确')</script>");               }           }           else           {               Response.Write("<script>alert('你还没有选择文件');</script>");           }           //如果扩展名符合条件，则上传           if (fileOk)           {               FileUpload1.PostedFile.SaveAs(path + FileUpload1.FileName);               Response.Write("<script>alert('上传成功');</script>");           }

try            {                //判断是否已经选取文件                if (FileUpload1.HasFile)                {                    if (IsAllowedExtension(FileUpload1))                    {                        string path = Server.MapPath("~/images/");                        FileUpload1.PostedFile.SaveAs(path + FileUpload1.FileName);                        Response.Write("<script>alert('上传成功');</script>");                    }                    else                    {                        Response.Write("<script>alert('您只能上传jpg或者gif图片');</script>");                    }                 }                else                {                    Response.Write("<script>alert('你还没有选择文件');</script>");                }            }            catch (Exception error)            {                Response.Write(error.ToString());            }            #endregion        }//真正判断文件类型的关键函数        public static bool IsAllowedExtension(FileUpload hifile)        {            System.IO.FileStream fs = new System.IO.FileStream(hifile.PostedFile.FileName, System.IO.FileMode.Open, System.IO.Fileaccess.Read);            System.IO.BinaryReader r = new System.IO.BinaryReader(fs);            string fileclass = "";            //这里的位长要具体判断.            byte buffer;            try            {                buffer = r.ReadByte();                fileclass = buffer.ToString();                buffer = r.ReadByte();                fileclass += buffer.ToString();             }            catch            {             }            r.Close();            fs.Close();            if (fileclass == "255216" || fileclass == "7173")//说明255216是jpg;7173是gif;6677是BMP,13780是PNG;7790是exe,8297是rar            {                return true;            }            else            {                return false;            }         }