thymeleaf doesn't update a model value in my template after a post

I have a session attribute called

@SessionAttributes("myNewAttribute")

which is defined at the top of my controller. when I hit my second endpoint, the post, the value does not update in thymleaf from blank to showing the string but it does print it to my console. I'm going a little crazy. Here is my controller file and my template:

@Controller
@SessionAttributes("myNewAttribute")
public class SpringFileController {
@GetMapping("/pageone")
    public String displayPageOne(Model model) {


        return "pageone";
    }

    @PostMapping("/clickedsavebutton")
    public String handleSaveButton(Model model){
        model.addAttribute("myNewAttribute","catnip");

        String valueToDisplay = (String)model.getAttribute("myNewAttribute");
        System.out.println(valueToDisplay);

        return "pageone";
    }
}

my template

<p th:text="${myNewAttribute}"></p>

<!--the save button, other things, wtc.. -->

So in my console when I click save I get "catnip" but "catnip" is not displayed on the page UNTIL I refresh the page. What am I doing wrong

edit: I added window.location.reload() after my post call in my template which makes the attribute show, but I lose other things on the page that have been changed if I do it this way

This is expected behavior, Thymeleaf is a rendering engine and as such can not change things after the initial load of the page.

To get the desired effect you'd have to reload (part) of your web page. this can be either a complete refresh or refreshing a div or field using something like ajax/javascript.

I added

$( "#required-field-div" ).load(window.location.href + " #required-field-div" );

to my function on the save button and got this to work. thank you for all the help!