How to set textbox value on listbox selection and send to servlet

Question

1st priority: Whenever i select any listbox item, value should set into hidden field id="driverName" but post should happen too so that i should be able to send the hidden field value to my servlet and perform query(for example: In servlet: String x = request.getParameter("driverName"); ). I read somewhere, post won't work on list item selection???

2nd option: If 1st option do not work then, when i select the listbox item, and click on search button, value should set into hidden field id="driverName" and should be able to get the into servlet (for example: In servlet: String x = request.getParameter("driverName"); )

Please give example of my code.

    HTML:
<input type="hidden" id="driverName" name="driverName" >
        <input type="submit" class="btn btn-info" onclick="selectedDriver();" value="Search"><br>
        <div class="multi-selectbox"> 
           <select size="10000" class="listbox-area" name="selectbox" id="selectbox" style="height: 550px;">
                            <%
                                List eList = (ArrayList)session.getAttribute("nameList");
                            %>
                            <% 
                                for (int i = 0; i < eList.size(); i++) {
                            %>
                            <option value=<%=((DriverName)eList.get(i)).getName()%>><%=((DriverName)eList.get(i)).getName()%></option>
                            <%
                                }
                            %>
                        </select>  
        </div>


My Javascript:

    <script type="text/javascript">
    function selectedDriver()
        {
        var hiddenttxt= document.getElementById("driverName"); 
            var hiddenttxt.value = "";
            var e = document.getElementById("selectbox");
            for(var i =0; i<e.options.length;i++)
                {
                    hiddenttxt.value +=e.options[i].value;
                    document.getElementById("driverName").value=hiddenttxt.value;
                }
        }
    </script>

Thank you