我试图使用TidHttp组件从Web检索大量图像.
问题是缺少许多图像(例如：7403,7412等)
我如何仅测试那些存在并将其保存到文件？
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;
解决方法
你不必为此做额外的事情.如果您尝试访问不存在的URL,HTTP服务器将报告TIdHTTP错误而不是包装到EIdHTTPProtocolException异常中.您不必先打扰调用TIdHTTP.Head(),因为您在保存之前将图像下载到TMemoryStream.您可以在单独调用TIdHTTP.Get()时捕获异常,根本不需要检查ResponseCode.
试试这个：
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;
实际上,您不需要TImage来将数据保存到文件中.如果您可以省略TImage.Picture.Assign()阶段,那么通过完全消除TJPEGImage(除非您尝试验证下载文件是有效的),代码更简单一点,例如：
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;
要么：
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;