压缩(zipped)文件夹是无效的Java

sourceFileName="./file.txt"'
                    sourceFile = new File(sourceFileName);

                    try {
                        // set the content type and the filename
                       responce.setContentType("application/zip");
                        response.addHeader("Content-Disposition","attachment; filename=" + sourceFileName + ".zip");
                        responce.setContentLength((int) sourceFile.length());


                        // get a ZipOutputStream,so we can zip our files together
                        ZipOutputStream outZip = new ZipOutputStream((responce.getOutputStream());

                        // Add ZIP entry to output stream.
                        outZip.putNextEntry(new ZipEntry(sourceFile.getName()));

                        int length = 0;
                        byte[] bbuf = new byte[(int) sourceFile.length()];

                        DataInputStream in = new DataInputStream(new FileInputStream(sourceFile));
                        while ((in != null) && ((length = in.read(bbuf)) != -1)) {
                            outZip.write(bbuf,length);
                        }

                        outZip.closeEntry();
                        in.close();
                        outZip.flush();
                        outZip.close();