Delphi实现判断网址是否存在及是否可以打开的方法

本例所述Delphi程序用于检测网址是否为404，也就是检测网址是否存在，或是否可以打开，针对不同的检查方法，会返回不同的结果。
程序主要代码如下：

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 beginStatusBar1.simpletext:="正在检验";NMHTTP1.Head（Edit1.Text）; end;end;end.