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 := 0 to LWebModule.ComponentCount - 1 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， ：）