---------------------------JS-------------------------------
<script type="text/javascript">
        function getValue(){
            var val = document.getElementById("testId").value;
            alert(val);
        }
    </script>
------------------------JSP---------------------------------
<form name="form2" action="" method="post">
        <table>
            <tr>
                <td>
                    <select id="testId" name="testName">
                        <option value="0"/>please select
                        <option value="1"/>America
                        <option value="2"/>China
                        <option value="3"/>England
                        <option value="4"/>Japan
                        <option value="5"/>Canada
                    </select>
                </td>
                <td><input type="button" onclick="getValue()" value="click me to get the select value"/></td>            
            </tr>
        </table>
    </form>