nullpointer exception when initalizing a class in servlet

Question

 class mstLeastCountEdit {
    mstLeastCount reff;
    HttpServletRequest request;
    HttpServletResponse response;
    String msg = "";
    String LcDesc="";
    int i = 0;
    int noOfRows = 0;
    HttpSession session=request.getSession(true);
    Integer ccode=(Integer) session.getAttribute("companycode");

    void updateEdit(mstLeastCount reff,HttpServletRequest request, HttpServletResponse response, int k)
    throws ServletException,IOException,IllegalStateException {
        int j = k;
        this.reff=reff;
        this.request=request;
        this.response=response;
        try{
             noOfRows = Integer.parseInt(request.getParameter("noOfRows"));
            String chkboxVal="";
            for(i=j;i<=noOfRows;i++) {
                if((request.getParameter("chk_select"+i))==null) {
                    chkboxVal="notticked";
                }//if for checked closed
                else {
                    chkboxVal=request.getParameter("chk_select"+i);
                    if(chkboxVal.equals("ticked")) {
                        String LcId=request.getParameter("txtLcId"+i);
                        String LcDesc=request.getParameter("txtLcDesc"+i);                                  
                        LcDesc=LcDesc.trim();
                        String Rec_Status=request.getParameter("RecStatus"+i);
                        Statement st=reff.con.createStatement();
                        String qu="xxxxxxxxxxxxxxxxx";
                        st.executeUpdate(qu);
                    }//if chkbox closed
                }//else checked closed
                //j+=1;
            }//For Loop Closed
        } catch(SQLException sql) {
            request.setAttribute("error", ge+" General e Exception");
            reff.getServletConfig().getServletContext().getRequestDispatcher("/errjsp.jsp").forward(request,response);
        } catch(Exception ge) {
            request.setAttribute("error", ge+" General e Exception");
            reff.getServletConfig().getServletContext().getRequestDispatcher("/errjsp.jsp").forward(request,response);
        }           
        ResultSet rs1 = null;
        try {
            Statement st1 = reff.con.createStatement();
            rs1 = st1.executeQuery("Select * from xxxx");
            ResultSetMetaData rsm = rs1.getMetaData();
            int col_Count = rsm.getColumnCount();
            Vector vrow = new Vector();
            while(rs1.next()) {
                Vector vcol = new Vector();
                for(int i=1;i<=col_Count;i++) {
                    vcol.addElement(rs1.getObject(i));
                }
                vrow.addElement(vcol);
            } //while loop closed
            request.setAttribute("vrow",vrow);
            request.setAttribute("msg",msg);
            reff.getServletConfig().getServletContext().getRequestDispatcher("/xxx.jsp").forward(request,response);
        }catch(SQLException sqldel){}
        return ;
    }
}   

the servlet is trying to call this class like this

mstLeastCountEdit ref1 = new mstLeastCountEdit();

and it throws nullpointer exception. i am still sloppy on the class , and this is a old code developed 10 years back, any will help ??

Answer 1

Glancing through the code...

HttpServletRequest request;

[...]

HttpSession session=request.getSession(true);
Integer ccode=(Integer) session.getAttribute("companycode");

This line should throw an exception. request has not been assign and so will be null, hence the NPE.

A servlet will typically be served between request and sessions. Even handling multiple requests at once. Therefore, do not store requests, sessions and related data within a servlet instance.

(As a matter of good practice: make fields private and where possible final, add spaces more conventionally, use camel caps for variable names (for instance companyCode) and don't abbreviate words particularly if they become meaningless.)

Answer 2

The line

HttpSession session=request.getSession(true);

is called before anything initializes request, so therefore you're trying to deference a null pointer.

Answer 3

The problem is in your field initializations:

HttpServletRequest request; 
HttpSession session=request.getSession(true);
Integer ccode=(Integer) session.getAttribute("companycode");

The first line initializes "request" to null, the second tries to use it.

Since you are passing the request into the method, there is no need to maintain it as a field members. Move those two lines into the body of the method. In fact, if you move all the fields into the body of the method - therby making them local variables - then there is no need to create a new "mstLeastCountEdit" on each request; in the servlet you can maintain a single reference to it as a member field.

And for the record, Java class names should start with a Capital letter.