Question

我有一个用Delphi XE6编写的Datasnap客户端服务器应用程序。我正在调用一个使用TFileStream创建临时文件的服务器方法，用我的http帖子中的TStream格式填充我的报告，并将其返回给我的客户端。这一切都按需要运作。但是，在方法结束时，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

在销毁文件流对象之前，无法删除您创建的文件流。文件流对象包装文件句柄，当文件句柄存在时，不能删除它后面的文件对象。

您需要销毁文件流对象才能删除它。

您的代码有一些奇怪的异常处理。它在函数中间不受歧视地吞下异常。你真的想要如此野蛮吗？在try / except块之外，任何异常都会导致文件流对象泄露。

在删除文件之前测试文件是否存在并没有太大意义。如果您成功创建了文件流，那么您可以确信该文件存在。

Answer 2

正如David所说，在TFileStream首先被销毁之前你无法删除文件，因此它可以关闭文件的句柄。如果您希望在使用服务器完成后自动删除文件，您可以：

直接使用Win32 CreateFile()函数打开文件，以便指定FILE_FLAG_DELETE_ON_CLOSE标志，然后使用THandleStream类包装生成的句柄。

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;

从TFileStream派生一个新类并覆盖其析构函数以删除该文件：

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;

使用this forum answer中显示的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;

在Delphi XE6中调用datasnap服务器方法后删除文件

2 个答案: