it appears to be too large for my current understanding
The complexity of the solution really depends on the specific context and functional requirements. It may seem overwhelming at first, but breaking down each concept (HTTP, HTML, CSS, JS, Java, JSP, Servlet, Ajax, JSON, etc) individually can help you grasp the bigger picture more effectively. You might benefit from checking out this answer for further insight.
If you want to implement it using just JSP/Servlet without Ajax, here is an example:
calculator.jsp:
<form id="calculator" action="calculator" method="post">
<p>
<input name="left">
<input name="right">
<input type="submit" value="add">
</p>
<p>Result: <span id="result">${sum}</span></p>
</form>
You would also need a CalculatorServlet mapped to /calculator in your web.xml file:
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
Integer left = Integer.valueOf(request.getParameter("left"));
Integer right = Integer.valueOf(request.getParameter("right"));
Integer sum = left + right;
request.setAttribute("sum", sum);
request.getRequestDispatcher("calculator.jsp").forward(request, response);
}
Implementing Ajax functionality is not as daunting as it seems. By including the following JavaScript code inside the HTML <head> section of your JSP, you can make it work seamlessly:
<script src="http://code.jquery.com/jquery-latest.min.js"></script>
<script>
$(document).ready(function() {
$('#calculator').submit(function() {
$form = $(this);
$.post($form.attr('action'), $form.serialize(), function(responseText) {
$('#result').text(responseText);
});
return false;
});
});
</script>
Don't forget to update the last part of your doPost method with the following lines:
response.setContentType("text/plain");
response.setCharacterEncoding("UTF-8");
response.getWriter().write(String.valueOf(sum));
To ensure compatibility with users who have disabled JavaScript, you can add a conditional check like this:
if ("XMLHttpRequest".equals(request.getHeader("X-Requested-With"))) {
response.setContentType("text/plain");
response.setCharacterEncoding("UTF-8");
response.getWriter().write(String.valueOf(sum));
} else {
request.setAttribute("sum", sum);
request.getRequestDispatcher("calculator.jsp").forward(request, response);
}