JSP将后台内容传到页面上，显示空指针

Question

这是错误
java.lang.NullPointerException
at org.apache.jsp.jsp.Cuisine.pagebreak_jsp._jspService(pagebreak_jsp.java:140)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:96)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:261)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:581)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:619)
这是JSP

序号	菜系	口味
${foodlist.id}	${foodlist.cuisine}	${foodlist.flavor}

这是Action
public class queryAction extends ActionSupport {
private static final long serialVersionUID = 1L;

FoodService service =new FoodService();

 public String execute() throws Exception{

  List foodlist =  service.selectFood();
  System.out.println(foodlist.toString());
ServletActionContext.getRequest().setAttribute("foodlist", foodlist);
ActionContext.getContext().getSession().put("foodlist",foodlist);
     if(foodlist!=null   && foodlist.size()>0){


         return "success";
     }
    else
         return "fail";

 }

这是Dao
public class FoodDao {
public Connection conn;
public Statement st;
public ResultSet rs;

public List selectFood(){
    List<Foodentity> empList = new ArrayList<Foodentity>();
    Connection conn = null;
    try{
        conn = this.getConn();
        st = conn.createStatement();
        rs = st.executeQuery("select * from caixi");
        while(rs.next()){
            Foodentity emp = new Foodentity();
            emp.setId(rs.getString("id"));
            emp.setCuisine(rs.getString("cuisine"));
            emp.setFlavor(rs.getString("flavor"));

            empList.add(emp);

        }
    }catch(Exception e){
        e.printStackTrace();
    }finally{
        try{
            if(rs != null)
                rs.close();
        }catch(Exception e){
            e.printStackTrace();
        }
        try{
            if(st != null)
                st.close();
        }catch(Exception e){
            e.printStackTrace();
        }
        try{
            if(conn != null)
                conn.close();
        }catch(Exception e){
            e.printStackTrace();
        }
    }
    return empList;

Answer 1

应该是你的jsp页面调用数据时出现了空值。也就是说你的 List foodlist = service.selectFood();这个方法里面有对象为空或者这个list为空。