一、 安全性比較低，把文本文件1.txt改成1.jpg照樣可以上傳，但其實現(xiàn)方法容易理解，實現(xiàn)也簡單，所以網(wǎng)上很多還是采取這種方法。

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Boolean fileOk = false;
  
  
  
          string path = Server.MapPath("~/images/");
  
  
  
          //判斷是否已經(jīng)選取文件
  
  
  
          if (FileUpload1.HasFile)
  
  
  
          {
  
  
  
              //取得文件的擴展名,并轉(zhuǎn)換成小寫
  
  
  
              string fileExtension = System.IO.Path.GetExtension(FileUpload1.FileName).ToLower();
  
  
  
              //限定只能上傳jpg和gif圖片
  
  
  
              string[] allowExtension = { ".jpg", ".gif" };
  
  
  
              //對上傳的文件的類型進行一個個匹對
  
  
  
              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("");
  
  
  
                  return;
  
  
  
              }
  
  
  
          }
  
  
  
          else
  
  
  
          {
  
  
  
              Response.Write("");
  
  
  
              return;
  
  
  
          }
  
  
  
          //如果擴展名符合條件，則上傳
  
  
  
          if (fileOk)
  
  
  
          {
  
  
  
              FileUpload1.PostedFile.SaveAs(path + FileUpload1.FileName);
  
  
  
              Response.Write("");
  
  
  
          }
 
 
 

二、不檢測文件后綴而是檢測文件MIME內(nèi)容類型。

 
 
 

  
  
  
Boolean fileOk = false;
  
  
  
           string path = Server.MapPath("~/images/");
  
  
  
           //判斷是否已經(jīng)選取文件
  
  
  
           if (FileUpload1.HasFile)
  
  
  
           {
  
  
  
               //取得文件MIME內(nèi)容類型
  
  
  
               string type = this.FileUpload1.PostedFile.ContentType.ToLower();
  
  
  
               if (type.Contains("image"))    //圖片的MIME類型為"image/xxx"，這里只判斷是否圖片。
  
  
  
               {
  
  
  
                   fileOk = true;
  
  
  
 
  
  
  
               }
  
  
  
               else
  
  
  
               {
  
  
  
                   Response.Write("");
  
  
  
               }
  
  
  
           }
  
  
  
           else
  
  
  
           {
  
  
  
               Response.Write("");
  
  
  
           }
  
  
  
           //如果擴展名符合條件，則上傳
  
  
  
           if (fileOk)
  
  
  
           {
  
  
  
               FileUpload1.PostedFile.SaveAs(path + FileUpload1.FileName);
  
  
  
               Response.Write("");
  
  
  
           }
 
 
 

三、可以實現(xiàn)真正意義上的文件類型判斷

 
 
 

  
  
  
try
  
  
  
            {
  
  
  
                //判斷是否已經(jīng)選取文件
  
  
  
                if (FileUpload1.HasFile)
  
  
  
                {
  
  
  
                    if (IsAllowedExtension(FileUpload1))
  
  
  
                    {
  
  
  
                        string path = Server.MapPath("~/images/");
  
  
  
                        FileUpload1.PostedFile.SaveAs(path + FileUpload1.FileName);
  
  
  
                        Response.Write("");
  
  
  
                    }
  
  
  
                    else
  
  
  
                    {
  
  
  
                        Response.Write("");
  
  
  
                    }
  
  
  
 
  
  
  
                }
  
  
  
                else
  
  
  
                {
  
  
  
                    Response.Write("");
  
  
  
                }
  
  
  
            }
  
  
  
            catch (Exception error)
  
  
  
            {
  
  
  
                Response.Write(error.ToString());
  
  
  
            }
  
  
  
            #endregion
  
  
  
        }
  
  
  
//真正判斷文件類型的關(guān)鍵函數(shù)
  
  
  
        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 = "";
  
  
  
            //這里的位長要具體判斷.
  
  
  
            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")//說明255216是jpg;7173是gif;6677是BMP,13780是PNG;7790是exe,8297是rar
  
  
  
            {
  
  
  
                return true;
  
  
  
            }
  
  
  
            else
  
  
  
            {
  
  
  
                return false;
  
  
  
            }
  
  
  
 
  
  
  
        }
 
 
 

文章標(biāo)題：ASP.net判斷上傳文件類型的三種方法
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