没有找到空指针异常，求大神指导

Question

org.apache.jasper.JasperException: An exception occurred processing JSP page /doSaveStudent.jsp at line 21

18: SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
19: student.setBorn(sdf.parse(born));
20: StudentDao sd = new StudentDao();
21: if (sd.add(student)) {
22: request.setAttribute("msg", "娣诲姞鎴愬姛锛�");
23: request.getRequestDispatcher("show.jsp").forward(request,
24: response);

Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:575)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:477)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause

java.lang.NullPointerException
util.BaseDao.update(BaseDao.java:55)
dao.ObjectDao.add(ObjectDao.java:17)
org.apache.jsp.doSaveStudent_jsp._jspService(doSaveStudent_jsp.java:86)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:439)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

Answer 1

这个dao的对象应该不是在程序中自己new出来的吧，自己new出来的可能会没有代理，应该是从已经管理起来的实例中获取的比较OK，很久没弄了，我就随便这么一说