ZipOutputStream produces corrupted zip file on Android

Question

I've implemented backup of user data from the app using zip archive, I am copying database and shared preferences files to zip archive and calculating MD5 checksum of input files to prevent user from modifying backup data.

To restore from archive I unzip backup file to temporary directory, check checksums and then copy preferences \ database file in the according folders.

Some of my users are complaining that the app generates corrupted backup files (zip files are indeed corrupted).

Here is code that compresses all files to zip file:

public void backup(String filename) {
    File file = new File(getBackupDirectory(), filename);
    FileOutputStream fileOutputStream = null;
    ZipOutputStream stream = null;
    try {
        String settingsMD5 = null;
        String databaseMD5 = null;
        if (file.exists())
            file.delete();
        fileOutputStream = new FileOutputStream(file);
        stream = new ZipOutputStream(new BufferedOutputStream(fileOutputStream));
        File database = getDatabasePath(databaseFileName);
        File dataDirectory = getFilesDir();
        if (dataDirectory != null) {
            File settings = new File(dataDirectory.getParentFile(), "/shared_prefs/" + PREFERENCES_FILENAME);
            settingsMD5 = zipFile("preferences", stream, settings);
        }
        databaseMD5 = zipFile("database.db", stream, database);

        JSONObject jsonObject = new JSONObject();
        try {
            jsonObject.put(META_DATE, new SimpleDateFormat(DATE_FORMAT, Locale.US).format(new Date()));
            jsonObject.put(META_DATABASE, databaseMD5);
            jsonObject.put(META_SHARED_PREFS, settingsMD5);
        } catch (Exception e) {
            e.printStackTrace();
        }

        InputStream metadata = new ByteArrayInputStream(jsonObject.toString().getBytes("UTF-8"));
        zipInputStream(stream, metadata, new ZipEntry("metadata"));
        stream.finish();
        stream.close();
        stream = null;
        return file;
    } catch (FileNotFoundException e) {
     //handling errrors
    } catch (IOException e) {
     //handling errrors
    } 
}

private String zipFile(String name, ZipOutputStream zipStream, File file) throws FileNotFoundException, IOException {
        ZipEntry zipEntry = new ZipEntry(name);
        return zipInputStream(zipStream, new FileInputStream(file), zipEntry);
    }

private String zipInputStream(ZipOutputStream zipStream, InputStream fileInputStream, ZipEntry zipEntry) throws IOException {
    InputStream inputStream = new BufferedInputStream(fileInputStream);
    MessageDigest messageDigest = null;
    try {
        messageDigest = MessageDigest.getInstance("MD5");
        if (messageDigest != null)
            inputStream = new DigestInputStream(inputStream, messageDigest);
    } catch (NoSuchAlgorithmException e) {
    }

    zipStream.putNextEntry(zipEntry);
    inputToOutput(inputStream, zipStream);
    zipStream.closeEntry();
    inputStream.close();

    if (messageDigest != null) {
        return getDigestString(messageDigest.digest());
    }
    return null;
}

private String getDigestString(byte[] digest) {
    StringBuffer hexString = new StringBuffer();
    for (int i = 0; i < digest.length; i++) {
        String hex = Integer.toHexString(0xFF & digest[i]);
        if (hex.length() == 1) {
            hex = new StringBuilder("0").append(hex).toString();
        }
        hexString.append(hex);
    }
    return hexString.toString();
}

private void inputToOutput(InputStream inputStream, OutputStream outputStream) throws IOException {
    byte[] buffer = new byte[BUFFER];
    int count = 0;
    while ((count = inputStream.read(buffer, 0, BUFFER)) != -1) {
        outputStream.write(buffer, 0, count);
    }
}

Answer 1

You might consider using the zip4j lib. I solved the problem I had ( same problem - different direction ) by using this lib. Some zip-files where not decodeable with the native android implementation, but with zip4j. You might also solve your problem by using zip4j for compression.