空指针的错不知道怎么改。。请大神们帮忙看下
exception
org.apache.jasper.JasperException: An exception occurred processing JSP page /bbs1.jsp at line 9
6: <%!
7: private void tree(Set<Article> articles,Connection conn, int id , int grade) {
8: String sql = "select * from article = " + id;
9: Statement stmt = DB.createStmt(conn);
10: ResultSet rs = DB.executeQuery(stmt,sql);
11: try{
12: while(rs.next()) {
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:588)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:481)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
root cause
java.lang.NullPointerException
com.bjsxt.servlet.DB.createStmt(DB.java:27)
org.apache.jsp.bbs1_jsp.tree(bbs1_jsp.java:26)
org.apache.jsp.bbs1_jsp._jspService(bbs1_jsp.java:148)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:443)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
note The full stack trace of the root cause is available in the Apache Tomcat/9.0.0.M10 logs.