java后台防止sql注入的方法

        String sql= "select * from users where username=? and password=?;
        PreparedStatement preState = conn.prepareStatement(sql);
        preState.setString(1, userName);
        preState.setString(2, password);
        ResultSet rs = preState.executeQuery();

    public static String SQL(String str)
    {
        return str.replaceAll(".*([‘;]+|(--)+).*", " ");
    }

    userName=SQL(userName);
    password=SQL(password);

    String sql="select * from users where username=‘"+userName+"‘ and password=‘"+password+"‘ "
    Statement sta = conn.createStatement();
    ResultSet rs = sta.executeQuery(sql);