在Struts 1.3中设置arraylist时出现空指针异常

Question

While I thought of setting array list value to array list bean it is returning null pointer exception. Please check action class:

public ActionForward execute(ActionMapping mapping, ActionForm form,
        HttpServletRequest request, HttpServletResponse response)
        throws Exception {

    ArrayList dailysheetdata;
    DailysheetForm dailyform = (DailysheetForm) form;
    Class.forName("com.mysql.jdbc.Driver");
    Connection connect = DriverManager.getConnection("jdbc:mysql://localhost/Stonecrusher?"
                        + "user=Stonecrusher&password=xxxxxx");
    System.out.println("Connection"+connect);
    dailysheetdata = StoneCrusherData.getDailysheetData(connect);
    if(dailysheetdata==null)
        System.out.println("dailysheetdata null");
    else if(dailyform==null)
    System.out.println("dailyform null");
    else
    dailyform.setArraylist(dailysheetdata) ;//iam getting exception here
    return mapping.findForward(SUCCESS);
     }

and my action form is

public class DailysheetForm extends ActionForm {
    // some getter and setter methods i used

    protected ArrayList arraylist;
    public ArrayList getArraylist() {
        return arraylist;
    }

    public void setArraylist(ArrayList arraylist) {

        this.arraylist = arraylist;

    }

When I run it I get following exception and in Tomcat log it is showing "dailyform is null"

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: java.lang.NullPointerException
    org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:520)
    org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:427)
    org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:228)
    org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
    org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:449)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

root cause

java.lang.NullPointerException
    com.myapp.struts.DialysheetListAction.execute(DialysheetListAction.java:59)
    org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:425)
    org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:228)
    org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
    org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:449)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.27 logs.

I am not able to find the reason. Please help to solve it and please state the reason.

Answer 1

Problem is DailysheetForm class object is not created by framework.

reasons are you din't configure FormBean class and Action class are properly in struts-config.xml

First you should check what page(which data ?) is submitted to action class ie

DailysheetForm dailyform = (DailysheetForm) form; 

check this line you are type casting form into DailysheetForm type object then framework automatically call the setter methods of DailysheetForm action form so maybe here you are getting NullPointerException i think so check it..

and One more thing you have to check in struts-config.xml entries ie in <action> tab name attribute value must be match with <form-beans> mappings check the package names also...