Preventing NullPointerException error on empty result set returned in JDBC

Question

I need advice on how I can avoid java.lang.NullPointerException when dealing with JDBC result set which I put on Swing components such as JTable

I have written a method which gets the result set encapsulated in an object from a DAO Implementation which I populate inside a DefaultTableModel.

The problems is, the object returned by the dao implementation service may or may not have data/result set if the database table has no record yet.

This results to a NullPointerException

public DefaultTableModel getMiscellaneous(int gradeLevelId){
        DefaultTableModel defaultTableModel = new DefaultTableModel();
        String[] columns = {"Name","Amount"};
        MiscellaneousFees miscellaneousFees =  schoolFeesDaoImpl.getMiscellaneous(gradeLevelId);
        List<Fee> feeList = miscellaneousFees.getFees();
        for(Fee fee: feeList){
            Object[] rowData = {fee.getName(),fee.getAmount()};
            defaultTableModel.addRow(rowData);
        }
        defaultTableModel.setColumnIdentifiers(columns);
        return defaultTableModel;
    }

public MiscellaneousFees getMiscellaneous(int gradeLevelId) {
        MiscellaneousFees miscellaneousFees = new MiscellaneousFees();
        List<Fee> feeList = new ArrayList<>();

        String SQL = "{CALL getMiscellaneousFeesByGradeLevelId(?)}";
        try (Connection con = DBUtil.getConnection(DBType.MYSQL);
                CallableStatement cs = con.prepareCall(SQL);){
            cs.setInt(1, gradeLevelId);
            try(ResultSet rs = cs.executeQuery();){
                while(rs.next()){
                    SchoolYear schoolYear = new SchoolYear();
                    schoolYear.setSchoolYearId(rs.getInt("schoolyear_id"));
                    schoolYear.setYearFrom(rs.getInt("yearFrom"));
                    schoolYear.setYearTo(rs.getInt("yearTo"));
                    schoolYear.setIsActive(rs.getBoolean("isActive"));
                    schoolYear.setStart_date(rs.getDate("start_date"));
                    schoolYear.setEnd_date(rs.getDate("end_date"));
                    schoolYear.setIsCurrentSchoolYear(rs.getBoolean("isCurrentSchoolYear"));

                    GradeLevel gradeLevel = new GradeLevel();
                    gradeLevel.setId(rs.getInt("gradelevel_id"));
                    gradeLevel.setLevel(rs.getInt("grade_level"));
                    gradeLevel.setIsActive(rs.getBoolean("isActive"));

                    FeeCategory feeCategory = new FeeCategory();
                    feeCategory.setCategory(rs.getString("fee_category"));
                    feeCategory.setId(rs.getInt("fee_category_id"));

                    Fee fee = new Fee();
                    fee.setId(rs.getInt("fee_id"));
                    fee.setName(rs.getString("fee_name"));
                    fee.setDescription(rs.getString("fee_description"));
                    fee.setAmount(rs.getDouble("fee_amount"));
                    fee.setFeeCategory(feeCategory);
                    fee.setGradeLevel(gradeLevel);
                    fee.setSchoolYear(schoolYear);
                    feeList.add(fee);
                }
                miscellaneousFees.setFees(feeList);
            }
        } catch (SQLException e) {
            JOptionPane.showMessageDialog(null,e.getMessage());
        }
        return miscellaneousFees;
    }

Any suggestion or advice of how I can prevent the NullPointerException when result set contained in the miscellaneous object is empty?

I get the NullPointerException error in this line of code

MiscellaneousFees miscellaneousFees =  schoolFeesDaoImpl.getMiscellaneous(gradeLevelId);

Thank you.

miscellaneous isn't null, it's schoolFeesDaoImpl that is null. The question will soon be closed as duplicate by a NPE watcher :p — Turtle, May 24 '17 at 09:23
You won't get null back if there are no results; you always get at least an empty Resultset. — Steve Smith, May 24 '17 at 09:29
I forgot to include private static SchoolFeesDaoImpl schoolFeesDaoImpl; in my code above but I have the schoolFeeDaoImpl. I get the null error when the method is called by action listener. I'll read through the included link by @SergiyMedvynskyy. Sorry for the duplicate. Thanks. — heisenberg, May 24 '17 at 09:33

Nyamiou The Galeanthrope · Answer 1 · 2017-05-24T11:00:11.883

Don't set lists, that's a bad practice and results in those kind of issues. In your MiscellaneousFees you can have a list initialized as an empty ArrayList and instead of doing miscellaneousFees.setFees(feeList) with a newly created list, for every element you call miscellaneousFees.addFee(fee) (that will add the element to the internal list).

This way if you don't have any fee the list will be empty and not null, which make more sense. Also avoiding to expose the internal state (the list) of your object prevents people to do nasty code that change the behavior of your object in ways you didn't anticipated.

score 0 · Answer 2 · answered May 24 '17 at 09:31

0

schoolFeesDaoImpl is null. You haven't created it.

answered May 24 '17 at 09:31

Steve Smith

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Preventing NullPointerException error on empty result set returned in JDBC

2 Answers2