JSP中获得集合的异常问题！（求助！！）

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: An exception occurred processing JSP page /ch01/index.jsp at line 11

8: p=Integer.parseInt(pageStr);
9: }
10: MessageBiz messageBiz=new MessageBiz(); //留言业务类
11: List<Message> listMessage=messageBiz.listByPage(p);
12: int prep=p; //上一页
13: int nextp=p; //下一页
14: if (listMessage.size()>3){

Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:505)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:416)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)