ByteArrayOutputStream.size()返回0錯誤

           

            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            BufferedOutputStream output = new BufferedOutputStream(bos);
            BufferedInputStream input = new BufferedInputStream(new FileInputStream(file));
            byte[] buffer = new byte[4096];
            int n = -1;
            while ((n = input.read(buffer, 0, 4096)) > -1) {
                appLogger.debug("n=" + n);
                output.write(buffer, 0, n);
            }

            /**
             * 此處必須調用flush
             * 如果檔案大小小於4096，那麼由於資料都在buffer中，
             * 因此BufferedOutputStream內部的ByteArrayOutputStream
             * 根本沒有得到資料，因此其長度返回0
             */
            output.flush();

            appLogger.debug("ByteArrayLen=" + bos.size());