Unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, Unit2, ComCtrls, StdCtrls, ExtCtrls;
type
  TForm1 = class(TForm)
    Button1: TButton;
    ProgressBar1: TProgressBar;
    Button2: TButton;
    Button3: TButton;
    Memo1: TMemo;
    Button4: TButton;
    Edit1: TEdit;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure FormShow(Sender: TObject);
  private
    { Private declarations }
    fWeb: string;
    fDownLoadThread: TDownLoadThread;
  public
    { Public declarations }
    procedure OnShowProgress(DownCount: Integer);
    procedure OnGetFileSize(fileSize: Integer);
    procedure OnShowStatus(aString: string);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
  fDownLoadThread := TDownLoadThread.Create(True);
  fDownLoadThread.FreeOnTerminate := True;
  fDownLoadThread.OnDownLoadCount := OnShowProgress;
  fDownLoadThread.OnShowString := OnShowStatus;
  fDownLoadThread.OnGetFileSize := OnGetFileSize;
  fDownLoadThread.initDownLoad(fWeb);
  fDownLoadThread.Resume();
end;

procedure TForm1.OnShowProgress(DownCount: Integer);
begin
  if DownCount > ProgressBar1.Max then
    Exit
  else
    ProgressBar1.Position := DownCount;
end;

procedure TForm1.OnGetFileSize(fileSize: Integer);
begin
  ProgressBar1.Position := 0;
  ProgressBar1.Max := fileSize;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  fDownLoadThread.Terminate();
end;

procedure TForm1.Button3Click(Sender: TObject);
begin
  fDownLoadThread.Suspend();
end;

procedure TForm1.OnShowStatus(aString: string);
begin
  Memo1.Lines.Add(aString);
end;

procedure TForm1.FormShow(Sender: TObject);
begin
  // 页面是 http://www.bc-cn.net/Soft/kfyy/delphi/edu/200604/296.html
  fWeb := 'http://www.bc-cn.net/Soft/ShowSoftDown.asp?UrlID=1&SoftID=296';
  Edit1.Text := '目标地址：' + fWeb;
end;

end.

下载线程部分

unit Unit2;

interface

uses
  Classes, SysUtils, IdBaseComponent, IdComponent, IdTCPConnection, IdTCPClient,
  IdHTTP, IdFTP;

type
  TOnDownLoadCount = procedure(DownCount: Integer) of object;
  TOnShowString = procedure(aString: string) of object;
  TDownLoadThread = class(TThread)
  private
    { Private declarations }
    fDestFileName: string;
    fFileSize: Integer;
    FDestWebAddr: string;
    fIdHttp: TIdHTTP;
    fIdFtp: TIdFTP;
    fDownLoadItem: TFileStream;
    fOnDownLoadCount: TOnDownLoadCount;
    fOnShowString: TOnShowString;
    fOnGetFileSize: TOnDownLoadCount;
    procedure OnDownLoadWork(Sender: TObject; AWorkMode: TWorkMode;
  const AWorkCount: Integer);
    procedure OnWorkBegin(Sender: TObject; AWorkMode: TWorkMode;
  const AWorkCountMax: Integer);
    procedure OnStatus(axSender: TObject; const axStatus: TIdStatus;
  const asStatusText: String);
    procedure OnRedirect(Sender: TObject; var dest: String;
  var NumRedirect: Integer; var Handled: Boolean);
  protected
    procedure Execute; override;
  public
    constructor Create(CreateSuspended: Boolean);
    destructor Destroy(); override;
    procedure initDownLoad(aWeb: string);
    property OnDownLoadCount: TOnDownLoadCount write fOnDownLoadCount;
    property OnShowString: TOnShowString write fOnShowString;
    property OnGetFileSize: TOnDownLoadCount write fOnGetFileSize;
  end;

implementation
{ TDownLoadThread }

procedure TDownLoadThread.Execute;
begin
  { Place thread code here }
  try
    fIdHttp.Connect();
    fIdHttp.Head('/Soft/ShowSoftDown.asp?UrlID=1&SoftID=296');
  except
    if FDestWebAddr <> '' then
      fOnShowString('地址重定向到：' + FDestWebAddr)
    else
      fOnShowString('连接失败.');
  end;

  // 这里这里应该分析重定向后的地址FDestWebAddr，根据地址决定是http下载还是ftp下载 这里省略了。
  // 得到的地址是：ftp://down1:008@down1.bc-cn.net/down1_18/1_kfyy/5_delphi/edu/delphi7_zjjfbsyykf.rar
  // 分析地址应该使用ftp,并得到一下信息
  fIdFtp := TIdFTP.Create(nil);
  fIdFtp.User := 'down1';  // 用户名
  fIdFtp.Password := '008'; // 密码
  fIdFtp.Host := 'down1.bc-cn.net'; // 主机
  fIdFtp.Port := 21;        // 端口，可以不设，默认就是21的 ，这里用的是端口模式。
  fIdFtp.OnWork := Self.OnDownLoadWork; // 实现相应的事件，这是下载过程
  fIdFtp.OnWorkBegin := Self.OnWorkBegin;  // 下载开始
  fIdFtp.OnStatus := Self.OnStatus;
  fIdFtp.Connect();
  fFileSize := fIdFtp.Size('/down1_18/1_kfyy/5_delphi/edu/delphi7_zjjfbsyykf.rar');
  fOnShowString('文件大小： ' + IntToStr(fFileSize));
  fIdFtp.Get('/down1_18/1_kfyy/5_delphi/edu/delphi7_zjjfbsyykf.rar', fDownLoadItem);
end;

procedure TDownLoadThread.OnDownLoadWork(Sender: TObject; AWorkMode: TWorkMode;
  const AWorkCount: Integer);
begin
  if Self.Terminated then
  begin
    try
      TIdTCPConnection(Sender).DisconnectSocket();
    except
      fOnShowString(' DisconnectSocket');
    end;
  end;
  fOnDownLoadCount(AWorkCount);
  fOnShowString('目前下载量：' + IntToStr(AWorkCount));
end;

procedure TDownLoadThread.OnWorkBegin(Sender: TObject; AWorkMode: TWorkMode;
  const AWorkCountMax: Integer);
begin
  if fFileSize <> 0 then
    fOnGetFileSize(fFileSize);
end;

procedure TDownLoadThread.OnStatus(axSender: TObject; const axStatus: TIdStatus;
  const asStatusText: String);
begin
  fOnShowString(asStatusText);
end;  

procedure TDownLoadThread.initDownLoad(aWeb: string);
begin
  // 论坛的一个文件地址
  //aWeb = http://www.bc-cn.net/Soft/ShowSoftDown.asp?UrlID=1&SoftID=296
  // 这里分析得到主机名为 www.bc-cn.net， 要下载的文件是/Soft/ShowSoftDown.asp?UrlID=1&SoftID=296
  // 这里省略了
  fIdHttp.Host := 'www.bc-cn.net';
  fIdHttp.Port := 80;
  fIdHttp.HandleRedirects := True;   // 设置重定向
  fIdHttp.OnRedirect := Self.OnRedirect;
  fIdHttp.OnStatus := Self.OnStatus;
end;

constructor TDownLoadThread.Create(CreateSuspended: Boolean);
begin
  fIdHttp :=  TIdHTTP.Create(nil);
  inherited Create(CreateSuspended);
end;

destructor TDownLoadThread.Destroy();
begin
  fIdHttp.Free();
  inherited Destroy();
end;

procedure TDownLoadThread.OnRedirect(Sender: TObject; var dest: String;
  var NumRedirect: Integer; var Handled: Boolean);
var
  i: Integer;
begin
  i := LastDelimiter('/', dest);
  FDestWebAddr := dest;
  fDestFileName := Copy(dest, i + 1, Length(dest));
  fDownLoadItem := TFileStream.Create(fDestFileName, fmCreate);
end;

end.