如何判断URL格式是否符合规范？

<%
function checkisUrl(tmpString)
dim c,i
checkisUrl = true
tmpString=Lcase(trim(tmpString))
if left(tmpString,7)<>"http://" then tmpString="http://"&tmpString
for i = 8 to Len(checkisUrl)
c = Lcase(Mid(tmpString, i, 1))
if InStr("abcdefghijklmnopqrstuvwxyz_-./\", c) <= 0 and not IsNumeric(c) then
checkisUrl = false
exit function
end if
next
if Left(tmpString, 1) = "." or Right(tmpString, 1) = "." then
checkisUrl = false
exit function
end if
if InStr(tmpString, ".") <= 0 then
checkisUrl = false
response.Write "f3"
exit function
end if
if InStr(checkisUrl, "..") > 0 then
checkisUrl = false
end if
end function
%>
<%
if checkisUrl(request("u"))=true then
%>恭喜,你的URL通过!
<%
else
%>对不起,你的URL不合乎规范,请重新检查!
<%end if%>
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