Delphi实现判断网址是否存在及是否可以打开的方法

unit address;interfaceuses Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, Psock, NMHttp, StdCtrls, ComCtrls;type TForm1 = class(TForm)  Label1: TLabel;  Edit1: TEdit;  Button1: TButton;  NMHTTP1: TNMHTTP;  StatusBar1: TStatusBar;  procedure Button1Click(Sender: TObject);  procedure NMHTTP1Success(Cmd: CmdType);  procedure NMHTTP1Failure(Cmd: CmdType);  procedure NMHTTP1HostResolved(Sender: TComponent);  procedure NMHTTP1InvalidHost(var Handled: Boolean);  procedure NMHTTP1AuthenticationNeeded(Sender: TObject);  procedure NMHTTP1Connect(Sender: TObject);  procedure NMHTTP1ConnectionFailed(Sender: TObject);  procedure FormActivate(Sender: TObject);  procedure FormClose(Sender: TObject; var Action: TCloseAction);  procedure NMHTTP1Redirect(var Handled: Boolean);  procedure Edit1KeyDown(Sender: TObject; var Key: Word;   Shift: TShiftState); private  { Private declarations } public  { Public declarations } end;var Form1: TForm1;implementation{$R *.DFM}procedure TForm1.Button1Click(Sender: TObject);var url:string;begin url:=Edit1.Text; StatusBar1.simpletext:='正在检验'; NMHTTP1.Head(url);end;procedure TForm1.NMHTTP1Success(Cmd: CmdType);begin case cmd of CmdHEAD:  StatusBar1.SimpleText:='网址正确' end;end;procedure TForm1.NMHTTP1Failure(Cmd: CmdType);begin case cmd of CmdHEAD:  StatusBar1.SimpleText:='网址不正确，没有这个页面' end;end;procedure TForm1.NMHTTP1HostResolved(Sender: TComponent);begin StatusBar1.SimpleText:='正确解析主机名';end;procedure TForm1.NMHTTP1InvalidHost(var Handled: Boolean);begin StatusBar1.SimpleText:='不能解析主机名';end;procedure TForm1.NMHTTP1AuthenticationNeeded(Sender: TObject);begin StatusBar1.SimpleText:='需要身份验证';end;procedure TForm1.NMHTTP1Connect(Sender: TObject);begin StatusBar1.SimpleText:='连接到主机';end;procedure TForm1.NMHTTP1ConnectionFailed(Sender: TObject);begin StatusBar1.SimpleText:='连接主机失败';end;procedure TForm1.FormActivate(Sender: TObject);begin Edit1.Text:='http://www.';end;procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);begin NMHTTP1.Destroy;end;procedure TForm1.NMHTTP1Redirect(var Handled: Boolean);begin StatusBar1.SimpleText:='重定向到其它页面';end;procedure TForm1.Edit1KeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);begin if Key=VK_RETURN then begin  StatusBar1.simpletext:='正在检验';  NMHTTP1.Head(Edit1.Text); end;end;end.