js赋值后在jsp中获取不到值

<!-- JSP页面 -->
<form action="yourJspPage.jsp" method="post">
    <input type="hidden" id="hiddenField" name="hiddenField">
    <button type="button" onclick="submitForm()">Submit</button>
</form>

<script>
function submitForm() {
    var value = "你想传递的值";
    document.getElementById('hiddenField').value = value;
    document.forms[0].submit();
}
</script>

<%
String value = request.getParameter("hiddenField");
%>

<!-- JSP页面 -->
<button type="button" onclick="sendData()">Send Data</button>

<script>
function sendData() {
    var value = "你想传递的值";
    var xhr = new XMLHttpRequest();
    xhr.open("POST", "yourJspPage.jsp", true);
    xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    xhr.onreadystatechange = function() {
        if (xhr.readyState === 4 && xhr.status === 200) {
            // 处理响应
        }
    };
    xhr.send("value=" + encodeURIComponent(value));
}
</script>

<%
String value = request.getParameter("value");
%>