I am trying to check username available or not when a user tries to create his account. when a user types it's username there should be an instant check that username is available or not and it will show a message in just below the username box.

I was tried to achieve it by calling an Ajax but not able to understand what to return basically and how will it work, actually I am very new in Struts 2 , I am able to check the username but did not under what to return.

My Ajax Call

<script>
            $(document).ready(function () {
                $("input").blur(function () {
                    var input = $(this).val();
                    alert(input);
                    $.ajax({
                        url:'checkUsername',
                        method:"POST",
                        data:{username:input},
                        success:function(data)
                        {
                            if(data!='0'){
                                $('#availability').html('<span>not available</span>')
                                $('#update').attr("disabled",true);
                            }
                            else{
                                $('#availability').html('<span>available</span>')
                                $('#update').attr("disabled",false);
                            }
                        }
                    })
                });
            });
        </script>

checkUsername Action

public String checkUsername() {
        try {
            setCtr(admin.checkUsername(username));
            if (ctr > 0) {
                System.out.println(ctr);
                setNoData(false);
            } else {
                setNoData(true);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return "CHECKUSER";
    }

method to check username in dao

public int checkUsername(String username) throws Exception {
        ResultSet rs = null;
        Connection con = null;
        try {
            con = ConnectionManager.getConnection();
            System.out.println(username);
            String sql = "SELECT * FROM userinfo WHERE username =?";
            PreparedStatement ps = con.prepareStatement(sql);
            ps.setString(1, username);
            rs = ps.executeQuery();
            if (rs.next()) {
                return 1;
            }

        } catch (Exception e) {
            e.printStackTrace();

        } finally {
            if (con != null) {
                con.close();
            }
        }
        return 0;
    }
}

This method in dao is able to check the username but what to return in that ajax data which i am trying to check that the if rows > 0 it should print not available. How to return and how to check?
struts.xml

 <action name="checkUsername" class="com.redress.actions.AdminAction" method = "checkUsername"> </action>

Can anyone please correct me, how to achieve this?