java - Getting checkbox value(s) from a Servlet

Question

I have a servlet with MySQL database in it. It looks like this:

here is the piece of code for it:

out.println("<table id = "main_section" cellspacing="1" bgcolor="red" > ");
out.println ("<tr> ");
out.println("<td >NUMBER</td>");
out.println("<td >PAYMENT</td>");
out.println("<td >RECEIVER</td>");
out.println("<td >VALUE </td>");
out.println("<td >CHECKBOX</td>");
out.println("</tr>");
out.println("<tr>");
for (int i = 0; i < ex.getExpenses().size(); i++) {
    out.println("<td > " + ex.getExpenses().get(i) + "</td>");

    if (i>0 && (i+1)%4==0) {
        out.println("<td><input type="checkbox" name="checkbox"></td>");
        out.println("</tr><tr>");

    }     
}
out.println("</tr>");

What I need to do is to create a submit button that calculates the sum of VALUE of the checked boxes. for instance, if NUMBER 1 and 2 are checked the submit button should give the result of 5577.0 (VALUE 22.0+5555.0). Can anyone please help me with that?

Answer 1

First of all, you should learn about JSPs and generate your HTML markup from a JSP rather than from the servlet.

Now for your problem. Each of these rows comes from a database table. So each of these rows should have an ID (primary key). Assign the ID of the row to the value of the checkbox. When you submit your form, the servlet will receive all the IDs of the checked checkboxes. Get the values corresponding from these IDs from the database, and sum them (or execute a query that computes the sum directly):

<input type="checkbox" name="checkedRows" value="${idOfCurrentRow}">

In the servlet handling the form submission:

String[] checkedIds = request.getParameterValues("checkedRows");