Asp.net判断上传文件类型的三种方法

一、 安全性比较低，把文本文件1.txt改成1.jpg照样可以上传，但其实现方法容易理解，实现也简单，所以网上很多还是采取这种方法。

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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>" );            }

　　二、不检测文件后缀而是检测文件MIME内容类型。

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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>" );             }

　　三、可以实现真正意义上的文件类型判断

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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 ;              }            }

转载于:https://www.cnblogs.com/yxlove/articles/3561503.html