Multiple drop-down List problem

hello people,

i am facing a small problem to retrieve the multiple value from drop-down list. Following code are written, but the result is null or there is no result displayed after invoking this page. Many thanks for helping to solve this problem.

<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>JSP Page</title>
    </head>
    <body>
    
    <%
    if(request.getParameter("submit") != null )
    {             
          String[] arr = request.getParameterValues("dropdownlistgroup");
         
          for(int i=0; i<arr.length; i++)
          {           
              out.println("List Selected : " + arr[i] + "!");
          }    
    }
    else
    {
    %>
    <form action="ShowMultipleDropDownList.jsp" method="POST">
       
        <select name="dropdownlistgroup" size="5" multiple>
            <option value="Pop" selected>Pop</option>
            <option value="Jazz">Jazz</option>
            <option value="Classic">Classic</option>
            <option value="Country">Country</option>
            <option value="Blues">Blues</option>
            <option value="Bluegrass">Bluegrass</option>
            <option value="Rock">Rock</option>
        </select>
        <input type="submit" value="submit" />
        <input type="reset" value="reset" />
    </form>
    <%
    }
    %>   
    </body>
 
</html>

You should name your button.

<input type="submit" name="submit" value="submit" />