URL parameters not getting passed during javascript submit

I am doing form submit from javascript when a image is clicked. Below is the form tag in my code

The image is present in the form tag. When i click the image i call a java script method shown below

The problem I am facing is the page gets submitted but i am not able to receive the parameter "selection" in the server.
request.getParameter("selection") is coming as null.

It would be great if someone would help in resolving this problem. I tried googling but didn't get a solution.

Have you used a tool such as HttpFox to see if the parameter is actually on the request?

Hi Bear Bibeault . Thanks a lot for coming forward to help me.

I used httpFox. There is no parameter passed in the URL

Because this is a from submit, perhaps you should be adding the parameter as a hidden input?

I not able understand why i should pass it as hidden parameter. I am trying to pass the parameters in the url. Can you please explain this and why and how to pass it as hidden parameter

For more clarity i am pasting the entire code here

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<%@ page import="com.tictactoe.model.PlayGame" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Tic Tac Toe</title>
<script type="text/javascript">
const USER = "U";
const NOT_SELECTED = "N";
const COMPUTER = "C";
function selection(selected){
	theform = window.document.tictactoe;
	theform.action="GameAction?selection="+selected.id;
	theform.submit();
}
function loadGame()
{
	var id;
	<%
		PlayGame playGame = ((PlayGame)request.getSession().getAttribute("game"));
		if (playGame !=null){
			%>
			var data = <%=playGame.getGame() %>
			var winner =<%=request.getSession().getAttribute("gameWinner") %>
			<%
		}
	%>

if(data ){
		for(var row=0;row<3;row++){
			for(var col=0;col<3;col++){
				id=row+","+col;
				if(data[row][col] == NOT_SELECTED){
					document.getElementById(id).src="images/white.JPG";
				} else if(data[row][col] == USER){
					document.getElementById(id).src="X Black.JPG";
				} else {
					document.getElementById(id).src="O Black.JPG";
				}	
			}
		}
			
	}

if(winner != null){
		var span = document.createElement("span");
		var textNode =document.createTextNode(winner+" wins the game");
		span.appendChild(textNode);
		document.getElementsByTagName("body")[0].appendChild(span);
	}
}
</script>
</head>
<body onload="loadGame();">
<form name="tictactoe" id="tictactoe" method="GET" action="GameAction">
<table border="1">
	<tr><td><img id="0,0" src="images/white.JPG" onclick="selection(this);"></img></td><td><img id="0,1" src="images/white.JPG" onclick="selection(this);"></img></td><td><img id="0,2" src="images/white.JPG" onclick="selection(this);"></img></td></tr>
	<tr><td><img id="1,0" src="images/white.JPG" onclick="selection(this);"></img></td><td><img id="1,1" src="images/white.JPG" onclick="selection(this);"></img></td><td><img id="1,2" src="images/white.JPG" onclick="selection(this);"></img></td></tr>
	<tr><td><img id="2,0" src="images/white.JPG" onclick="selection(this);"></img></td><td><img id="2,1" src="images/white.JPG" onclick="selection(this);"></img></td><td><img id="2,2" src="images/white.JPG" onclick="selection(this);"></img></td></tr>
</table>
</form>
</body>
</html>

I found the solution. I changed the form method from GET to POST. for the parameters to get passed.
I would be great if someone could explain me why doesn't GET method doesn't work.