读DataSnap源代码（二）

program Project1;
{$APPTYPE GUI}

{$R *.dres}

uses
  Vcl.Forms,
  Web.WebReq,
  IdHTTPWebBrokerBridge,
  FormUnit1 in 'FormUnit1.pas' {Form1},
  ServerMethodsUnit1 in 'ServerMethodsUnit1.pas',
  WebModuleUnit1 in 'WebModuleUnit1.pas' {WebModule1: TWebModule};

{$R *.res}

begin
{ 返回是什么，见下面的【绿色代码】 }
  if WebRequestHandler <> nil then
    WebRequestHandler.WebModuleClass := WebModuleClass;
  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

IdHTTPWebBrokerBridge单元中：

 initialization
{** 挂钩 **}

 2   WebReq.WebRequestHandlerProc := IdHTTPWebBrokerBridgeRequestHandler;
 {$IFDEF HAS_CLASSVARS}
   {$IFNDEF HAS_CLASSDESTRUCTOR}
 finalization
   FreeAndNil(TIdHTTPWebBrokerBridgeRequestHandler.FWebRequestHandler);
   {$ENDIF}
 {$ELSE}
 finalization
   FreeAndNil(IndyWebRequestHandler);
 {$ENDIF}

WebRequestHandler是Web.WebReq中的一个方法：

 function WebRequestHandler: TWebRequestHandler;
 begin
   if Assigned(WebRequestHandlerProc) then
     Result := WebRequestHandlerProc     /** 指向 IdHTTPWebBrokerBridgeRequestHandler 函数了 **/
   else
     Result := nil;
 end;

IdHTTPWebBrokerBridgeRequestHandler的定义：

 function IdHTTPWebBrokerBridgeRequestHandler: TWebRequestHandler;
 begin
   {$IFDEF HAS_CLASSVARS}
   if not Assigned(TIdHTTPWebBrokerBridgeRequestHandler.FWebRequestHandler) then
     TIdHTTPWebBrokerBridgeRequestHandler.FWebRequestHandler := TIdHTTPWebBrokerBridgeRequestHandler.Create(nil);
   Result := TIdHTTPWebBrokerBridgeRequestHandler.FWebRequestHandler;
   {$ELSE}
   if not Assigned(IndyWebRequestHandler) then
     IndyWebRequestHandler := TIdHTTPWebBrokerBridgeRequestHandler.Create(nil);
   Result := IndyWebRequestHandler;
   {$ENDIF}
 end;

还记得（一）中的那个静态成员吗? 在第4行初始化了。

继续（一）中 Run 函数中的代码：

 procedure TIdHTTPWebBrokerBridgeRequestHandler.Run(AThread: TIdContext; ARequestInfo: TIdHTTPRequestInfo; AResponseInfo: TIdHTTPResponseInfo);
 var
   LRequest: TIdHTTPAppRequest;
   LResponse: TIdHTTPAppResponse;
 begin
   try
     LRequest := TIdHTTPAppRequest.Create(AThread, ARequestInfo, AResponseInfo);
     try
       LResponse := TIdHTTPAppResponse.Create(LRequest, AThread, ARequestInfo, AResponseInfo);
       try
         // WebBroker will free it and we cannot change this behaviour
         AResponseInfo.FreeContentStream := False;
         HandleRequest(LRequest, LResponse);
       finally
         FreeAndNil(LResponse);
       end;
     finally
       FreeAndNil(LRequest);
     end;
   except
     // Let Indy handle this exception
     raise;
   end;
 end;

TIdHTTPWebBrokerBridgeRequestHandler并没有 override 父类(TWebRequestHandler)的HandleRequest方法. 看TWebRequestHandler.HandleRequest代码

 function TWebRequestHandler.HandleRequest(Request: TWebRequest;
   Response: TWebResponse): Boolean;
 var
   I: Integer;
   LWebModule: TComponent;
   LWebAppServices: IWebAppServices;
   LGetWebAppServices: IGetWebAppServices;
   LComponent: TComponent;
 begin
   Result := False;
   LWebModule := ActivateWebModules;
   if Assigned(LWebModule) then
   try
     try
       if Supports(IInterface(LWebModule), IGetWebAppServices, LGetWebAppServices) then
         LWebAppServices := LGetWebAppServices.GetWebAppServices;
       if LWebAppServices = nil then
         for I :=  to LWebModule.ComponentCount -  do
         begin
           LComponent := LWebModule.Components[I];
           if Supports(LComponent, IWebAppServices, LWebAppServices) then
             if LWebAppServices.Active then
               break
             else
               LWebAppServices := nil;
         end;
       if LWebAppServices = nil then
         LWebAppServices := TDefaultWebAppServices.Create;
       LWebAppServices.InitContext(LWebModule, Request, Response);
       try
         try
           Result := LWebAppServices.HandleRequest;
         except
           ApplicationHandleException(LWebAppServices.ExceptionHandler);
         end;
       finally
         LWebAppServices.FinishContext;
       end;
       if Result and not Response.Sent then
         Response.SendResponse;
     except
       ApplicationHandleException(LWebAppServices.ExceptionHandler);
     end;
   finally
     DeactivateWebModules(LWebModule);
   end;
 end;

在上面代码中，可以看到 WebModule 字眼了， ：）