比较jsp页面的值与数据库值空指针异常

Question

i want to compare the strings that are taken from form with the values with the table values... but there is nullpointerexception
2)how do i get resultset to not access the last record of the table

        String occid = request.getParameter("occid");
        String date = request.getParameter("Date");
        String firstname = request.getParameter("FirstName");
        String lastname = request.getParameter("LastName");
        String village = request.getParameter("Village");
        String sonof = request.getParameter("Son");
        String district = request.getParameter("District");
        String weight = request.getParameter("Weight");
        String bags = request.getParameter("Bags");
        String rate = request.getParameter("Rate");
        String amount = request.getParameter("Amount");
        String advanceamt = request.getParameter("Advance");

        String sql = null;
        PreparedStatement prest = null;
        List<AcceptBean> list = new ArrayList<AcceptBean>();

        sql = "Select * from ColdStorage.OccupantMaster";
        prest = conn.prepareStatement(sql);
        ResultSet rs = prest.executeQuery();
        String first = "";
        String last = "";
        String vill = "";
        String son = "";
        String dist = "";
        while (rs.next()) {
            AcceptBean bean = new AcceptBean();
            first = rs.getString("FirstName");
            bean.setFirstName(first);
            System.out.println("first = " + first);
            last = rs.getString("LastName");
            bean.setLastName(last);
            System.out.println("last = " + last);
            vill = rs.getString("Village");
            bean.setVillage(vill);
            System.out.println("vill = " + vill);
            son = rs.getString("Sonof");
            bean.setSonOf(son);
            System.out.println("son = " + son);
            dist = rs.getString("District");
            bean.setDistrict(dist);
            System.out.println("dist = " + dist);
            list.add(bean);
        }
        for (AcceptBean s : list) {
            if ((first.equals(firstname) || first.equals("null")) && (last.equals(lastname) || last.equals("null")) &&
                    (vill.equals(village) || vill.equals("null")) && (son.equals(sonof) || son.equals("null")) &&
                    (dist.equals(district) || dist.equals("null"))) 

            {
                System.out.println("do nothing");
                ServletContext sc = getServletContext();
                RequestDispatcher rd = sc.getRequestDispatcher("/Index.jsp");
                System.out.println("it exists in database");
                rd.forward(request, response);

            } 

the database values are -

OccId FirstName LastName Village SonOf District

31 Sourodeep bag bengal aurobindo bad bengal

32 ARVINDBHAI PARMAR SAJOD PARAGBHAI SAJOD

67 divyang parmar bharuch Arvindbhai bharuch

72 urvashi parmar mumbai arvindbhai parmar mumbai

90 divyang NULL NULL NULL NULL

91 divyang NULL NULL NULL NULL

Answer 1

1. You have to Check for null

   if(first!=null)

2.If it is a null stirng, then null not equals NULL because you have used equals , use equalsIgnoreCase Instead.

Answer 2

The docs for ResultSet#getString say:

the column value; if the value is SQL NULL, the value returned is null

So last is null for those rows for example, not the String "null" . You are therefore calling null.equals .

Test for == null , not equals("null") :

        if( first == null || first.equals(firstname) &&
            last == null || last.equals(lastname) &&
            vill == null || vill.equals(village) &&
            son == null || son.equals(sonof) &&
            dist == null || dist.equals(district) )

Answer 3

check your

if(first!=null)

then compare the values with other