public RussianLowerCaseFilter(TokenStream in,
    char[] charset) 
{
        super(in);
        this.charset = charset;
}

 public final Token next() throws IOException 
{
        Token t = input.next();
        if (t == null)
            return null;
        String txt = t.termText();
        char[] chArray = txt.toCharArray();
        for (int i = 0; i <  chArray.length; i++)
        {
            chArray[i] = RussianCharsets.toLowerCase(chArray[i], charset);
        }
        String newTxt = new String(chArray);
        // create new token
        Token newToken = new Token(newTxt, t.startOffset(), t.endOffset());
        return newToken;
}