Load new Realm file from assets when a migration is required

RealmAssetLoaderHelperMethods.java

public Realm loadAssetFileOnMigration() {

    // TODO Don't re-create this every time
    RealmConfiguration config = new RealmConfiguration.Builder()
            .schemaVersion(2) // Bumping the schema because new app
            .build();

    Realm realm;
    try {
        realm = Realm.getInstance(config);
    } catch (RealmMigrationNeededException e) {
        // A migration was required. Delete the old file and load a
        // new from the asset folder.
        Realm.deleteRealm(config);
        copyAssetFile(getContext(), "assetFileName", config);
        realm = Realm.getInstance(config); // This should now succeed
    }
    return realm;
}

// Modified copy of https://github.com/realm/realm-java/blob/master/realm/realm-library/src/main/java/io/realm/RealmCache.java#L340
private void copyAssetFile(Context context, String assetFileName, RealmConfiguration configuration) {
    IOException exceptionWhenClose = null;
        File realmFile = new File(configuration.getRealmDirectory(), configuration.getRealmFileName());
        InputStream inputStream = null;
        FileOutputStream outputStream = null;
        try {
            inputStream = context.getAssets().open(assetFileName);
            if (inputStream == null) {
                throw new IOException("Could not open asset file: " + assetFileName);
            }
            outputStream = new FileOutputStream(realmFile);
            byte[] buf = new byte[4096];
            int bytesRead;
            while ((bytesRead = inputStream.read(buf)) > -1) {
                outputStream.write(buf, 0, bytesRead);
            }
        } catch (IOException e) {
            // Handle IO exceptions somehow
            throw new RuntimeException(e);
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    exceptionWhenClose = e;
                }
            }
            if (outputStream != null) {
                try {
                    outputStream.close();
                } catch (IOException e) {
                    // Ignores this one if there was an exception when close inputStream.
                    if (exceptionWhenClose == null) {
                        exceptionWhenClose = e;
                    }
                }
            }
        }

        // No other exception has been thrown, only the exception when close. So, throw it.
        if (exceptionWhenClose != null) {
            throw new RuntimeException(exceptionWhenClose);
        }
}