delphi - Delphi XE6 中 datasnap 服务器方法调用后文件删除

Question

我有一个用 Delphi XE6 编写的 Datasnap 客户端服务器应用程序。我正在调用一个服务器方法，该方法使用 TFileStream 创建临时文件，用我的 http 帖子中的 TStream 格式的报告填充它，然后将其返回给我的客户端。这一切都按需要进行。但是，在该方法的最后，我调用deleteFile方法从服务器中删除临时文件，但它永远不会被删除。我做错了什么？

var
  r,f: String;
  SS: TStringStream;
  Uid: TGuid;
begin
   CreateGuid(Uid);
   f:= ChangeFileExt(GuidToString(Uid),'.rpt');
   result:= TFileStream.Create(f, fmCreate or fmOpenWrite);

  r := getRunReportJSON(ARunReportObj);
  SS := TStringStream.Create(r, TEncoding.ASCII);
  try
    try      
      ServerContainer1.idHttp1.Post(gUrl, SS, result);
      Result.Position:= 0;
    except
    end;
  finally
    SS.Free;
    if FileExists(f) then
      DeleteFile(f)
  end;
end;

Answer 1

正如 David 所说，在首先销毁 TFileStream 以便它可以关闭文件句柄之前，您无法删除该文件。如果您希望服务器使用完该文件后自动删除该文件，您可以:

1. 直接使用 Win32 CreateFile() 函数打开文件，以便您可以指定 FILE_FLAG_DELETE_ON_CLOSE 标志，然后使用 包装生成的句柄THandleStream 类。

   type
     TMyHandleStream = class(THandleStream)
     public
       destructor Destroy; override;
     end;
   
   destructor TMyHandleStream.Destroy;
   begin
     inherited;
     CloseHandle(Handle);
   end;
   
   var
     h: THandle;
     r, f: String;
     SS: TStringStream;
     Uid: TGuid;
   begin
     CreateGuid(Uid);
     f := 'C:\some folder\' + GuidToString(Uid) + '.rpt';
     h := Windows.CreateFile(PChar(f), GENERIC_READ or GENERIC_WRITE, FILE_SHARE_READ, nil, CREATE_ALWAYS, FILE_FLAG_DELETE_ON_CLOSE, 0);
     if h = INVALID_HANDLE_VALUE then RaiseLastOSError;
     Result := TMyHandleStream.Create(h);
     try
       r := getRunReportJSON(ARunReportObj);
       SS := TStringStream.Create(r, TEncoding.ASCII);
       try
         ServerContainer1.IdHTTP1.Post(gUrl, SS, Result);
       finally
         SS.Free;
       end;
       Result.Position := 0;
     except
       Result.Free;
       raise;
     end;
   end;
   

2. 从 TFileStream 派生一个新类并重写其析构函数以删除文件:

   type
     TMyFileStream = class(TFileStream)
     public
       destructor Destroy; override;
     end;
   
   destructor TMyFileStream.Destroy;
   begin
     inherited;
     DeleteFile(Self.FileName);
   end;
   

   var
     r, f: String;
     SS: TStringStream;
     Uid: TGuid;
   begin
     CreateGuid(Uid);
     f := 'C:\some folder\' + GuidToString(Uid) + '.rpt';
     Result := TMyFileStream.Create(f, fmCreate or fmOpenReadWrite);
     try
       r := getRunReportJSON(ARunReportObj);
       SS := TStringStream.Create(r, TEncoding.ASCII);
       try
         ServerContainer1.IdHTTP1.Post(gUrl, SS, Result);
       finally
         SS.Free;
       end;
       Result.Position := 0;
     except
       Result.Free;
       raise;
     end;
   end;
   

3. 使用 this forum answer 中所示的 TFileStreamEx 类:

   type
     TFileStreamEx = class(THandleStream)
     public
       constructor Create(const FileName: string; Mode: Word; flags: DWORD = FILE_ATTRIBUTE_NORMAL);
       destructor Destroy; override;
     end;
   
   constructor TFileStreamEx.Create(const FileName: string; Mode: Word; flags: DWORD = FILE_ATTRIBUTE_NORMAL);
   const
     AccessMode: array[0..2] of LongWord = (
       GENERIC_READ,
       GENERIC_WRITE,
       GENERIC_READ or GENERIC_WRITE);
     ShareMode: array[0..4] of LongWord = (
       0,
       0,
       FILE_SHARE_READ,
       FILE_SHARE_WRITE,
       FILE_SHARE_READ or FILE_SHARE_WRITE);
   begin
     if Mode = fmCreate then
     begin
       inherited Create(
         CreateFile(
           PChar(FileName),
           GENERIC_READ or GENERIC_WRITE,
           0,
           nil,
           CREATE_ALWAYS,
           flags,
           0
         )
       );
       if Handle = INVALID_HANDLE then
         raise EFCreateError.CreateFmt(SFCreateError, [FileName]);
     end
     else
     begin
       inherited Create(
         CreateFile(
           PChar(FileName),
           AccessMode[Mode and 3],
           ShareMode[(Mode and $F0) shr 4],
           nil,
           OPEN_EXISTING,
           flags,
           0
         )
       );
       if Handle = INVALID_HANDLE then
         raise EFOpenError.CreateFmt(SFOpenError, [FileName]);
     end;
   end;
   
   destructor TFileStreamEx.Destroy;
   begin
     if Handle <> INVALID_HANDLE then CloseHandle(Handle);
   end;
   

   var
     r, f: String;
     SS: TStringStream;
     Uid: TGuid;
   begin
     CreateGuid(Uid);
     f := 'C:\some folder\' + GuidToString(Uid) + '.rpt';
     Result := TFileStreamEx.Create(f, fmCreate or fmOpenReadWrite, FILE_FLAG_DELETE_ON_CLOSE);
     try
       r := getRunReportJSON(ARunReportObj);
       SS := TStringStream.Create(r, TEncoding.ASCII);
       try
         ServerContainer1.IdHTTP1.Post(gUrl, SS, Result);
       finally
         SS.Free;
       end;
       Result.Position := 0;
     except
       Result.Free;
       raise;
     end;
   end;