新手跟着视频做一个BBS项目，做到展示帖子的JSP的时候一直报错
type Exception report
message An exception occurred processing JSP page /articleDetail.jsp at line 23
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 /articleDetail.jsp at line 23
20: String sql="select*from article where rootid ="+id+"order by pdate asc";
21: Statement stmt=DB.creatStmt(conn);
22: ResultSet rs=DB.executeQuery(stmt, sql);
23: while (rs.next()){
24: Article a=new Article();
25: a.initFromRs(rs);
26: articles.add(a);
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
root cause
java.lang.NullPointerException
org.apache.jsp.articleDetail_jsp._jspService(articleDetail_jsp.java:87)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
这是个啥情况啊，它说23行那里有错，就那个while那里，可是我怎么看都看不出有错误啊
