Jsp无法向数据库添加除数字以外的字符

向数据库添加信息的代码为：

    byte b1[] = request.getParameter("name").getBytes("ISO-8859-1");
    String na = new String(b1);
    byte b2[] = request.getParameter("email").getBytes("ISO-8859-1");
    String em = new String(b2);
    byte b3[] = request.getParameter("title").getBytes("ISO-8859-1");
    String ti = new String(b3);
    byte b4[] = request.getParameter("content").getBytes("ISO-8859-1");
    String co = new String(b4);
    if (na == null)
        na = "";
    if (ti == null)
        ti = "";
    if (co == null)
        co = "";
    if (em == null)
        em = "";
    try { // 将获得的留言信息装入数据库
        PreparedStatement stm = con
                .prepareStatement("insert into liuyanban_table (title,name,email,content) values('"+ti+"','"+na+"','"+em+"','"+co+"')");



        try {
            stm.executeQuery();
        } catch (Exception e) {
        }
        // 对留言板中“查看留言”的请求, 服务器端重定向给另一个Servlet来控制
        RequestDispatcher requestDispatcher = request
                .getRequestDispatcher("ViewMessages_servlet");
        requestDispatcher.forward(request, response);
    } catch (Exception e) {
        e.printStackTrace();

数据库对应字段类型对不对？