JSP无法连接数据库，不知道是不是tomcat配置有问题

HTTP Status 500 -
The server encountered an internal error () that prevented it from fulfilling this request.
exception

org.apache.jasper.JasperException: An exception occurred processing JSP page /index.jsp at line 40
37:  </tr>
38:  <%
39:  List listMainBoard=(List)mapBoard.get(new Integer(0));
40:  for(int i=0;i <listMainBoard.size();i++){
41:  Board mainBoard=(Board)listMainBoard.get(i);
42:    %>
43:    <tr class="tr3">

org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:554)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:431)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:319)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)


root cause

java.lang.NullPointerException
org.apache.jsp.index_jsp._jspService(index_jsp.java:104)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:389)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:319)
org.apache.jasper