delphi – 如何使用IdHTTP检查URL？

为了处理所有异常,正如你所说,忽略它们,你可以使用与@ Stijn的代码几乎相同的代码：

procedure TForm1.Button1Click(Sender: TObject);
var
  IdHTTP: TIdHTTP;
begin
  IdHTTP := TIdHTTP.Create;
  try
    try
      IdHTTP.Get('http://www.example.com');
    except
      // do just nothing here,if you really want to completely ignore all 
      // exceptions thrown from inside the try..except block execution and
      // if you don't want to indicate somehow,that the exception occured
    end;
  finally
    IdHTTP.Free;
  end;
end;

2.如何处理TIdHTTP抛出的特定异常？

也许有一天你会想要对TIdHTTP课程抛出的某些类型的异常做出反应,例如仅对HTTP协议异常作出反应.这就是我在这里尝试阐述的.

Indy为不同场合定义了许多异常类,当某个操作失败时可能会发生异常类.以下是异常类的列表,您可能会在使用HTTP协议时感兴趣：

> EIdException – 它是Indy库使用的基础异常类.当您想区分Indy引发的异常和应用程序抛出的所有其他异常时,可能对您有用.
> EIdSocketError – 从HTTP协议抽象的角度来看,它是一个低级异常类,涵盖了某个套接字操作失败时引发的所有异常.这可能对您的检测有用,您的网络级别有问题.
> EIdConnClosedGracefully – 此类引发的异常表示服务器端以常见方式关闭与客户端的连接.当您需要对这种情况作出反应时,这可能很有用,例如通过重新连接到服务器.
> EIdHTTPProtocolException – 当处理特定请求的HTTP响应时发生错误时,此异常类用于抛出异常.当从HTTP响应接收到意外的数字HTTP响应代码时,通常会发生这种情况.当您想要具体处理HTTP协议错误时,这可能很有用.通过这种异常处理,您可以例如对服务器响应返回的某些HTTP状态代码做出反应.

以下是处理上述异常的代码框架.当然,你不必显示消息,而是做更有用的事情.而且,你不需要处理它们;它在你的哪些例外和你将如何处理：

uses
  IdHTTP,IdException,IdStack;

procedure TForm1.Button1Click(Sender: TObject);
var
  IdHTTP: TIdHTTP;
begin
  IdHTTP := TIdHTTP.Create;
  try
    try
      IdHTTP.Get('http://www.example.com');
    except
      // this exception class covers the HTTP protocol errors; you may read the
      // response code using ErrorCode property of the exception object,or the
      // same you can read from the ResponseCode property of the TIdHTTP object
      on E: EIdHTTPProtocolException do
        ShowMessage('Indy raised a protocol error!' + sLineBreak +
          'HTTP status code: ' + IntToStr(E.ErrorCode) + sLineBreak +
          'Error message' + E.Message);
      // this exception class covers the cases when the server side closes the
      // connection with a client in a "peaceful" way
      on E: EIdConnClosedGracefully do
        ShowMessage('Indy reports,that connection was closed gracefully!');
      // this exception class covers all the low level socket exceptions
      on E: EIdSocketError do
        ShowMessage('Indy raised a socket error!' + sLineBreak +
          'Error code: ' + IntToStr(E.LastError) + sLineBreak +
          'Error message' + E.Message);
      // this exception class covers all exceptions thrown by Indy library
      on E: EIdException do
        ShowMessage('Indy raised an exception!' + sLineBreak +
          'Exception class: ' + E.ClassName + sLineBreak +
          'Error message: ' + E.Message);
      // this exception class is a base Delphi exception class and covers here
      // all exceptions different from those listed above
      on E: Exception do
        ShowMessage('A non-Indy related exception has been raised!');
    end;
  finally
    IdHTTP.Free;
  end;
end;