Message from server to client in Alert window

I have this

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    char[] charArray = reverse(request.getParameter("field").toCharArray());
    PrintWriter out = response.getWriter();

}

public char[] reverse(char[] array){
    int id = 0;
    char[] newArr = new char[array.length];
    for(int i=array.length-1; i >= 0; i--){
        newArr[id] = array[i];
        id++;
    }
    return newArr;      
}

How can i hand off charArray to the main WebPage in AlertWindow? Please, help.