ASP.net判断上传文件类型的三种有效方法

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;
}
}