HTTP?Status?500?-?null type?Exception?report message?null description?The?server?encountered?an?internal?error?that?prevented?it?from?fulfilling?this?request. exception java.lang.NumberFormatException:?null java.lang.Integer.parseInt(Unknown?Source) java.lang.Integer.parseInt(Unknown?Source) com.bzjy.servlet.ProductClassServlet.doPost(ProductClassServlet.java:71) com.bzjy.servlet.ProductClassServlet.doGet(ProductClassServlet.java:49) javax.servlet.http.HttpServlet.service(HttpServlet.java:624) javax.servlet.http.HttpServlet.service(HttpServlet.java:731) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) com.bzjy.filter.CharSetFilter.doFilter(CharSetFilter.java:27) note?The?full?stack?trace?of?the?root?cause?is?available?in?the?Apache?Tomcat/7.0.70?logs. Apache?Tomcat/7.0.70 public?void?doPost(HttpServletRequest?request,?HttpServletResponse?response) throws?ServletException,?IOException?{ int?id=Integer.parseInt(request.getParameter("id")); int?flag=Integer.parseInt(request.getParameter("flag")); if(flag==0){ ProductParentBiz?ppbiz=new?ProductParentBizImpl(); ppbiz.delParentCate(id); }else{ ProductCategoryBiz?pcbiz=new?ProductCategoryBizImpl(); pcbiz.delChildCate(id); } response.sendRedirect("ProductClassServlet"); }