Thymeleaf: How to get selected item on click - thymeleaf

Question

I want to call a method with the clicked object as a param.
Problem: on every reload or button press the method is called for every element.
<form action="#" th:action="#{/}" th:object="${chessBoard}" method="post">
<table>
<tr th:each="i, iter1: *{board}">
<td th:each="item, iter2: ${i}">
<button th:onclick="${chessBoard.selected(item)}" th:text="${item.text}"></button>
</td>
<tr>
</table>
</form>

Answer 1

You don't need the onclick method in your form to submit a parameter.
You can simply pass a parameter to the controller with a RequestedParam annotation in your controller.
It will be something like:
<form th:action="#{/}" method="post">
<table>
<tr th:each="i: ${board}">
<td th:each="item: ${i}">
<button name="item" th:value="${item.id}" th:text="${item.text}"/>
</td>
<tr>
</table>
</form>
and in your controller:
#PostMapping (path = "/")
public String test(Model model, #RequestParam(name = "item") int id) {
System.out.println(id);
}
A second option is to use an attribute that you add to your model and you get back in your controller with something like:
#PostMapping("/")
public String greetingSubmit(#ModelAttribute ChessBoard chessBoard, Model model) {...}
Html will be something like
<form th:action="#{/}" th:object="${chessBoard}" method="post">
<table>
<tr th:each="i: ${board}">
<td th:each="item: ${i}">
<button th:field="*{id}" th:value="${item.id}" th:text="${item.text}"/>
</td>
<tr>
</table>
</form>