Delphi DataSnap 流程分析(二)

Delphi DataSnap 流程分析(一)_看那山瞧那水的博客-优快云博客

粗略分析了 创建传统DataSnap的流程，现在再分析下创建现在更常用的 方式：

DataSnap REST Application

这种方式只支持HTTP(普通HTTP和REST HTTP)通信，不支持TCP通信。

 这种方式包含有WebModule，HTTP服务器也是TIdHTTPWebBrokerBridge

 因此其HTTP Server的启动流程和 Delphi Web Server 流程分析_看那山瞧那水的博客-优快云博客

里分析的一样，只是到了最后，也就是方法TCustomWebDispatcher.DispatchAction()，接着进行后续处理。

代码： 

constructor TCustomWebDispatcher.Create(AOwner: TComponent);
var
  I: Integer;
  Component: TComponent;
  SetAppDispatcher: ISetAppDispatcher;
begin
{$IFDEF MSWINDOWS}
{$ENDIF}
  FDispatchList := TObjectList<TComponent>.Create;//TComponentList.Create;
  FDispatchList.OwnsObjects := False;
  FOnException := nil;
  if AOwner <> nil then
    if AOwner is TCustomWebDispatcher then
      raise EWebBrokerException.Create(sOnlyOneDispatcher)
    else
      for I := 0 to AOwner.ComponentCount - 1 do
        if AOwner.Components[I] is TCustomWebDispatcher then
          raise EWebBrokerException.Create(sOnlyOneDispatcher);
  inherited CreateNew(AOwner, -1);
  FActions := TWebActionItems.Create(Self, TWebActionItem);
  if Owner <> nil then
    for I := 0 to Owner.ComponentCount - 1 do
    begin
      Component := Owner.Components[I];
      if Supports(IInterface(Component), ISetAppDispatcher, SetAppDispatcher) then
        SetAppDispatcher.SetAppDispatcher(Self)
      else if Supports(IInterface(Component), IWebDispatch) then
        FDispatchList.Add(Component);
    end;
end;

TCustomWebDispatcher类创建的时候，会加载支持接口IWebDispatch的组件，TDSHTTPWebDispatcher是支持IWebDispatch接口的:

TDSHTTPWebDispatcher = class(TDSHTTPServerTransport, IWebDispatch) 

所以FDispatchList列表包含了WebModule的组件DSHTTPWebDispatcher1。

 
function TCustomWebDispatcher.DispatchAction(Request: TWebRequest;
  Response: TWebResponse): Boolean;
var
  I: Integer;
  Action, Default: TWebActionItem;
  Dispatch: IWebDispatch;
begin
  FRequest := Request;
  FResponse := Response;
  I := 0;
  Default := nil;
  if Response.Sent then
  begin
    Result := True;
    { Note that WebSnapSvr enabled apps have no way to mark response as sent }
    Exit;
  end;
  Result := DoBeforeDispatch(Request, Response) or Response.Sent;
  while not Result and (I < FActions.Count) do
  begin
    Action := FActions[I];
    Result := Action.DispatchAction(Request, Response, False);
    if Action.Default then Default := Action;
    Inc(I);
  end;
  // Dispatch to self registering components
  I := 0;
  while not Result and (I < FDispatchList.Count) do
  begin
    if Supports(IInterface(FDispatchList.Items[I]), IWebDispatch, Dispatch) then
    begin
      Result := DispatchHandler(Self, Dispatch,
        Request, Response, False);
    end;
    Inc(I);
  end;
 
  if not Result and Assigned(Default) then
    Result := Default.DispatchAction(Request, Response, True);
  if Result and not Response.Sent then
    Result := DoAfterDispatch(Request, Response);
 
end;

如果前面没有中断，则执行下面的代码：

  // Dispatch to self registering components
  I := 0;
  while not Result and (I < FDispatchList.Count) do
  begin
    if Supports(IInterface(FDispatchList.Items[I]), IWebDispatch, Dispatch) then
    begin
      Result := DispatchHandler(Self, Dispatch,
        Request, Response, False);
    end;
    Inc(I);
  end;

因而执行Dispatch := DSHTTPWebDispatcher1(TDSHTTPWebDispatcher类)，

DispatchHandler(): 这是一个局部方法

function DispatchHandler(Sender: TObject; Dispatch: IWebDispatch; Request: TWebRequest; Response: TWebResponse;
  DoDefault: Boolean): Boolean;
begin
  Res