FTPClient.retrieveFile返回false，但仍下载文件

Question

我正在尝试使用此代码从FTP服务器检索文件。

private class FtpTask extends AsyncTask<Void, Void, Long> {
    protected Long doInBackground(Void... args) {

        FTPClient FtpClient = new FTPClient();
        int reply;

        try {
            FtpClient.connect(ftpServer);
            FtpClient.login(ftpUser, ftpPass);

            reply = FtpClient.getReplyCode();

            if (FTPReply.isPositiveCompletion(reply)) {
                String remoteFileName = "ACPlus.ZIP";
                String localFile = context.getFilesDir() + "/ACPLUS.ZIP";

                // Delete local file first
                File file = new File(localFile);
                if(file.exists()) {
                    file.delete();
                }

                FtpClient.changeWorkingDirectory("/" + ftpFolder);
                FtpClient.setFileType(FTPClient.BINARY_FILE_TYPE);
                FtpClient.enterLocalPassiveMode();

                OutputStream outputStream = null;

                boolean success = false;
                try {
                    outputStream = new BufferedOutputStream(new FileOutputStream(localFile));
                    success = FtpClient.retrieveFile(remoteFileName, outputStream);

                    reply = FtpClient.getReplyCode();
                }
                finally {
                    if (outputStream != null) {
                        outputStream.close();
                    }
                }

                bConnected = success;
            }
            else
            {
                bConnected = false;
            }
        }
        catch (Exception ex) {
            return null;
        }

        return null;
    }

    protected void onPostExecute(Long result) {
        super.onPostExecute(result);

        if (bConnected == true) {
            // Extract local file
            File file = new File(context.getFilesDir() + "/ACPLUS.ZIP");
            if(file.exists()) {

            }
        }
        else
        {
            AlertDialog.Builder msg = new AlertDialog.Builder(context);
            msg.setTitle("Error");
            msg.setMessage("Connection could not be established!");
            msg.setPositiveButton("OK", new DialogInterface.OnClickListener() {
              @Override
                public void onClick(DialogInterface dialog, int which) {
                    // Do nothing
                }
            });

            AlertDialog dialog = msg.create();
            dialog.show();
        }
    }

作为测试，我单步执行了代码，然后到达

// Delete local file first
   File file = new File(localFile);
   if(file.exists()) {
        file.delete();
    }

我停止调试，所以我知道该文件已被删除。然后，我再次开始逐步执​​行。这次它错过了file.delete();if语句为false，因此证明删除文件已成功完成。

然而，当我继续步，当我到达了线success = FtpClient.retrieveFile(remoteFileName, outputStream);，success有值false，这意味着我onPostExecute并没有经过正确的代码。

但是，当再次对其进行调试时，这次它确实通过了if语句并删除了本地文件，表明它实际上已经下载，尽管success = false另有说明。

我是否误解了某件事，或者这是通常的行为？