Using TidHttp to download Jpeg images from URL (only those that exist)? - delphi

Question

I am trying to retrieve a large number of images from the web using a TidHttp component.
The problem is that there is a number of images that are missing (Example: 7403, 7412, etc)
How do i test for only those that exist and save those to file?
procedure TForm.Button1Click(Sender: TObject);
var
MS : TMemoryStream;
JPEGImage: TJPEGImage;
Url, numString: String;
I, Code: Integer;
begin
for I := 7400 to 7500 do
begin
{
Url :='http://www.mywebpage.com/images/DSC' + numString+ '.jpg';
try
idhttp1.Head(URL);
code := idhttp1.ResponseCode;
except on E: EIdHTTPProtocolException do
code := idhttp1.ResponseCode;
end;//try except
if code = 200 then
begin
MS := TMemoryStream.Create;
JPEGImage := TJPEGImage.Create;
try
try
idhttp1.Get(Url, MS); //Send the request and get the image
code := idhttp1.ResponseCode;
MS.Seek(0,soFromBeginning);
JPEGImage.LoadFromStream(MS);//load the image in a Stream
Image1.Picture.Assign(JPEGImage);//Load the image in a Timage component
Image1.Picture.SaveToFile('C:\Museum_Data\DSC' + numString + '.jpg');
Application.ProcessMessages;
except
on E: EIdHTTPProtocolException do
code := idhttp1.ResponseCode; // or: code := E.ErrorCode;
end; //try except
finally
MS.free;
JPEGImage.Free;
end; //try finally
end; //if
end;
end;

Answer 1

You don't have to do anything extra for that. If you try to access a non-existant URL, the HTTP server will report an error that TIdHTTP than wraps into an EIdHTTPProtocolException exception. You do not have to bother with calling TIdHTTP.Head() first, since you are downloading the images to a TMemoryStream before saving them. You can catch the exception when calling TIdHTTP.Get() by itself, no need to check the ResponseCode at all.
Try this:
procedure TForm.Button1Click(Sender: TObject);
var
MS: TMemoryStream;
JPEG: TJPEGImage;
Url: String;
I: Integer;
begin
MS := TMemoryStream.Create;
try
JPEG := TJPEGImage.Create;
try
for I := 7400 to 7500 do
begin
Url := 'http://www.mywebpage.com/images/DSC' + IntToStr(I) + '.jpg';
MS.Clear;
try
IdHTTP1.Get(Url, MS);
except
on E: EIdHTTPProtocolException do
Continue;
end;
MS.Position := 0;
JPEG.LoadFromStream(MS);
Image1.Picture.Assign(JPEG);
JPEG.SaveToFile('C:\Museum_Data\DSC' + IntToStr(I) + '.jpg');
Application.ProcessMessages;
end;
finally
JPEG.Free;
end;
finally
MS.Free;
end;
end;
You do not actually need the TImage in order to save the data to file. If you can omit the TImage.Picture.Assign() stage, then the code a bit simpler by eliminating the TJPEGImage altogether (unless you are trying to validate the download files are valid), eg:
procedure TForm.Button1Click(Sender: TObject);
var
MS: TMemoryStream;
Url: String;
I: Integer;
begin
MS := TMemoryStream.Create;
try
for I := 7400 to 7500 do
begin
Url := 'http://www.mywebpage.com/images/DSC' + IntToStr(I) + '.jpg';
MS.Clear;
try
IdHTTP1.Get(Url, MS);
except
on E: EIdHTTPProtocolException do
Continue;
end;
MS.Position := 0;
MS.SaveToFile('C:\Museum_Data\DSC' + IntToStr(I) + '.jpg');
Application.ProcessMessages;
end;
finally
MS.Free;
end;
end;
Or:
procedure TForm.Button1Click(Sender: TObject);
var
FS: TFileStream;
Url, FileName: String;
I: Integer;
begin
for I := 7400 to 7500 do
begin
Url := 'http://www.mywebpage.com/images/DSC' + IntToStr(I) + '.jpg';
FileName := 'C:\Museum_Data\DSC' + IntToStr(I) + '.jpg';
FS := TFileStream.Create(FileName, fmCreate);
try
try
try
IdHTTP1.Get(Url, FS);
except
on E: EIdHTTPProtocolException do
Continue;
end;
Application.ProcessMessages;
finally
Fs.Free;
end;
except
DeleteFile(FileName);
end;
end;
end;