用Delphi检测一个url地址是否正确

前面在做文件下载的时候，有时会遇到url指定的文件并不存在，所以在下载过程中会出现一些错误，尽管这些错误可以except掉，但还是需事先检测一下，如果url不正确则不用再调用download过程了。下面的函数可以进行检测并函数返回boolean型值：

1 function TFrameChannel.CheckUrl(url: string; TimeOut: Integer = 5000): boolean;

2 var

3 hSession, hfile : hInternet;

4 dwindex, dwcodelen: dword;

5 dwcode: array[1..20] of char;

6 res: pchar;

7 re: integer;

8 Err1: integer;

9 j: integer;

10 begin

11 if pos('http://', lowercase(url)) = 0 then

12 url := 'http://' + url;

13 Result := false;

14 hSession := nil;

15 hFile := nil;

16

17 //设置超时

18 InternetSetOption(hSession, Internet_OPTION_CONNECT_TIMEOUT, @TimeOut, 4);

19 hSession := InternetOpen('Mozilla/4.0', INTERNET_OPEN_TYPE_PRECONFIG, nil, nil, 0);

20 if assigned(hsession) then begin

21 j := 1;

22 while true do begin

23 hfile := InternetOpenUrl(hsession, pchar(url), nil, 0, INTERNET_FLAG_RELOAD, 0);

24 if hfile = nil then begin

25 j := j + 1;

26 Err1 := GetLastError;

27 if j > 5 then break;

28 if (Err1 <> 12002) or (Err1 <> 12152) then break;

29 sleep(2);

30 end else begin

31 break;

32 end;

33 end;

34 dwIndex := 0;

35 dwCodeLen := 10;

36 HttpQueryInfo(hfile, HTTP_QUERY_STATUS_CODE, @dwcode, dwcodeLen, dwIndex);

37 res := pchar(@dwcode);

38 re := strtointdef(res, 404);

39 case re of

40 400..450: result := false;

41 else result := true;

42 end;

43 if assigned(hfile) then

44 InternetCloseHandle(hfile);

45 InternetCloseHandle(hsession);

46 end;

47 end;

48