Please help me ! new to jsp

Question

I am getting null pointer exception when i am trying to execute one combox to populate the other combo box. I am not able to understand where i am doing wrong. if anybody can guide me will be greatly appreciated,
My code in the servlet is
resultSet = statement.executeQuery("SELECT * from kiosk_hitcount where kiosk_name like 'Altoona%' and l_category ='" + request.getParameter("category") + "' group by l_categoryb order by l_categoryb asc");
Vector data = new Vector();
while(resultSet.next())
String rowdata= resultSet.getString("l_categoryb");
data.addElement(rowdata);
request.getSession().setAttribute("data", data);
RequestDispatcher rd = getServletContext().getRequestDispatcher("/MyKiosk/CategoryTest.jsp");
rd.forward(request,response);
in jsp page:
<tr><td><Font size='2'><H3>Local Sub-Category:</H3></Font></td>
<td><SELECT name="bcategory">
<%
Vector data = new Vector();
data = (Vector)request.getSession().getAttribute("data");
for(int i = 0; i< data.size(); i++)
String catb = (String)data.get(i);
%>
<OPTION value="<%= catb%>" ><%= catb%></OPTION>
<%
%>
</SELECT></TD></TR>
Thank you ,
Mary

Answer 1

Here is the stackTrace for the Exception
java.lang.NullPointerException
at MyKiosk._0002fMyKiosk_0002fCategoryTest_0002ejspCategoryTest_jsp_82._jspService(_0002fMyKiosk_0002fCategoryTest_0002ejspCategoryTest_jsp_82.java:176)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:119)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.jasper.servlet.JspServlet$JspServletWrapper.service(JspServlet.java:177)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:318)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:391)
at org.netbeans.modules.web.tomcat.JspServlet.service(JspServlet.java:91)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.tomcat.core.ServletWrapper.doService(ServletWrapper.java:404)
at org.apache.tomcat.core.Handler.service(Handler.java:286)
at org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
at org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:797)
at org.apache.tomcat.core.ContextManager.service(ContextManager.java:743)
at org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:210)
at org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)
at org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:498)
at java.lang.Thread.run(Thread.java:484)