从数据库中获取值时，Jtable中的按钮未显示

Question

So basically the requirement is to fetch results from database based on the search query. Results are displayed in JTable. The results should have 5 columns. The 4 columns contain values fetched from database. The 5th column is supposed to have buttons . When the button is clicked a popup should appear. Now the search functionality is working fine. I'm getting an error when I need to display a buttons in 5th column. I googled and found out that it can be done by TablCellRenderer. I've also incorporated the code for the same in my code referring this link Now, I get the error as

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at r_search_2$JTableButtonRenderer.getTableCellRendererComponent(r_search_2.java:193)

which lies in this block:-

             else
            {
                button.setForeground(table.getForeground());
                button.setBackground(UIManager.getColor("Button.background"));
            }

If I remove this block from my code the search query runs fine but buttons are not displayed in the 5th column. So where lies the error and how should I correct that ? Thanks !

import java.awt.*;
import java.awt.event.*;
import java.io.File;
import java.sql.*;
import java.util.Vector;
import javax.swing.*;
import javax.swing.table.DefaultTableModel;
import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.UIManager;
import javax.swing.table.AbstractTableModel;
import javax.swing.table.TableCellRenderer;


public class r_search_2 extends JFrame implements ActionListener
{

    JFrame frame1;
    JLabel l0, l1, l2;
    JComboBox c1;
    JButton b1;
    Connection con;
    ResultSet rs, rs1;
    Statement st, st1;
    PreparedStatement pst;
    String ids;
    static JTable table  = new JTable(new JTableModel());
   // static JTable table  = new JTable();
    String[] columnNames = {"SECTION NAME", "REPORT NAME", "CONTACT", "LINK","METRICS"};
    String from;
    Vector v = new Vector();
    JMenuBar menu = new JMenuBar();
    JPanel mainPanel = new JPanel(new BorderLayout());
    JPanel topPanel = new JPanel(new FlowLayout(SwingConstants.LEADING, 60,25));
    JScrollPane scroll = new JScrollPane(table);

    r_search_2() 
    {

        l1 = new JLabel("Search");
        b1 = new JButton("submit");
        l1.setBounds(75, 110, 75, 20);
        b1.setBounds(150, 150, 150, 20);
        b1.addActionListener(this);

        topPanel.add(l1,BorderLayout.LINE_START);

        try 
        {

            File dbFile = new File("executive_db.accdb");
                String path = dbFile.getAbsolutePath();
                con = DriverManager.getConnection("jdbc:odbc:Driver={Microsoft Access Driver (*.mdb, *.accdb)}; DBQ= " + path);
                Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
            st = con.createStatement();
            rs = st.executeQuery("select index_name from Index1");
           while (rs.next())
           {
                ids = rs.getString(1);
                v.add(ids);

            }
            c1 = new JComboBox(v);
            c1.setEditable(true);c1.setSelectedItem("");
            c1.setBounds(150, 110, 150, 20);
            topPanel.add(c1,BorderLayout.CENTER);
            topPanel.add(b1,BorderLayout.LINE_END);
            mainPanel.add(topPanel, BorderLayout.PAGE_START);

            st.close();
            rs.close();
        } 
        catch (Exception e)
        {
        }
       // setVisible(true);
    }

    public void actionPerformed(ActionEvent ae) 
    {
        if (ae.getSource() == b1)
        {
            showTableData();
        }
     }

    public void showTableData()
    {

        DefaultTableModel model = new DefaultTableModel();
        model.setColumnIdentifiers(columnNames);

        table.setModel(model);
        table.setAutoResizeMode(JTable.AUTO_RESIZE_ALL_COLUMNS);
        table.setFillsViewportHeight(true);

        scroll.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        scroll.setVerticalScrollBarPolicy( JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);
        from = (String) c1.getSelectedItem();


        TableCellRenderer buttonRenderer = new JTableButtonRenderer();
        table.getColumn("METRICS").setCellRenderer(buttonRenderer);
        //System.out.println(table.getColumn("METRICS"));
        //table.getColumn("Button2").setCellRenderer(buttonRenderer);
        table.addMouseListener(new JTableButtonMouseListener(table));

        String section_name = "";
        String report_name = "";
        String contact_name = "";
        String link = "";


        try
        {

        pst = con.prepareStatement("select distinct Section.Section_Name,Report.Report_Name,Report.Link,Contact.Contact_Name "
                                        + "FROM (( Section INNER JOIN Report ON Report.Section_ID=Section.Section_ID ) INNER JOIN Contact ON Contact.Contact_ID=Report.Contact_ID )  LEFT JOIN Metrics ON Metrics.Report_ID=Report.Report_ID  "
                                                                + " WHERE Section.Section_Name LIKE '%"+from+"%' OR Report.Report_Name LIKE '%"+from+"%' OR Metrics.Metric_Name LIKE '%"+from+"%' OR Contact.Contact_Name LIKE '%"+from+"%' ");
            ResultSet rs = pst.executeQuery();
            int i = 0;
            while (rs.next()) {
                section_name = rs.getString("Section_Name");
                report_name = rs.getString("Report_Name");
                contact_name = rs.getString("Contact_Name");
                link = rs.getString("Link");
               // String m="apple";

                model.addRow(new Object[]{section_name, report_name, contact_name, link});

                i++;
            }

            if (i < 1)
            {
                JOptionPane.showMessageDialog(null, "No Record Found", "Error", JOptionPane.ERROR_MESSAGE);
            }
            if (i == 1)
            {
                System.out.println(i + " Record Found");
            } else {
                System.out.println(i + " Records Found");
            }
        } 
        catch (Exception ex) 
        {
            JOptionPane.showMessageDialog(null, ex.getMessage(), "Error", JOptionPane.ERROR_MESSAGE);
        }
        mainPanel.add(scroll);

        mainPanel.revalidate();
        mainPanel.repaint();

    }
    private static class JTableButtonRenderer implements TableCellRenderer
    {       
        @Override public Component getTableCellRendererComponent(JTable table, Object value, boolean isSelected, boolean hasFocus, int row, int column) {
            JButton button = (JButton)value;
            if (isSelected) {
                button.setForeground(table.getSelectionForeground());
                button.setBackground(table.getSelectionBackground());
            } 
            else
            {
                button.setForeground(table.getForeground());
                button.setBackground(UIManager.getColor("Button.background"));
            }
            return button;  
        }
    }

    private static class JTableButtonMouseListener extends MouseAdapter
    {
        private final JTable table;

        public JTableButtonMouseListener(JTable table)
        {
            this.table = table;
        }

        public void mouseClicked(MouseEvent e)
        {
            int column = table.getColumnModel().getColumnIndexAtX(e.getX());
            int row    = e.getY()/table.getRowHeight(); 

            if (row < table.getRowCount() && row >= 0 && column < table.getColumnCount() && column >= 0)
            {
                Object value = table.getValueAt(row, column);
                if (value instanceof JButton) 
                {
                    ((JButton)value).doClick();
                }
            }
        }
    }

    public static class JTableModel extends AbstractTableModel 
    {

        private static final long serialVersionUID = 1L;
        //private static final String[] COLUMN_NAMES = new String[] {"Id", "Stuff", "METRICS"};
          String[] columnNames = {"SECTION NAME", "REPORT NAME", "CONTACT", "LINK","METRICS"};
        private static final Class<?>[] COLUMN_TYPES = new Class<?>[] {String.class, String.class,String.class, String.class,  JButton.class};

        @Override public int getColumnCount()
        {
            return columnNames.length;
        }

        @Override public int getRowCount()
        {
            return 4;
        }

        @Override public String getColumnName(int columnIndex)
        {
            return columnNames[columnIndex];
        }

        @Override public Class<?> getColumnClass(int columnIndex)
        {
            return COLUMN_TYPES[columnIndex];
        }

        @Override public Object getValueAt(final int rowIndex, final int columnIndex)
        {
            switch (columnIndex) {
                case 0: //return rowIndex;
                case 1: //return "Text for "+rowIndex;
                case 2: // fall through
                case 3: final JButton button = new JButton(columnNames[columnIndex]);
            //  button.setPreferredSize(new Dimension(100, 100));
                button.setSize(new Dimension(10,10));
                        button.addActionListener(new ActionListener() {
                            public void actionPerformed(ActionEvent arg0) {
                                JOptionPane.showMessageDialog(JOptionPane.getFrameForComponent(button), 
                                        "Button clicked for row "+rowIndex);
                            }
                        });
                        return button;
                default: return "";
            }
        }   
    }


    public static void main(String args[])
    {


                r_search_2 s=new r_search_2();
                //new r_search_2();
                JFrame fr=new JFrame("Search Executive Reports");
                //fr.add(s.getUI());
                fr.add(s.mainPanel);
                fr.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                fr.setLocationByPlatform(true);
                fr.setSize(1000, 400);
                //fr.pack();
                fr.setVisible(true);

      //  new r_search_2();
    }
}

Answer 1

Don't use a MouseListener for this; use a TableCellEditor , illustrated here . Conveniently, DefaultCellEditor can delegate to a JComboBox as a popup component.

Answer 2

There is something is wrong with below code in JTableButtonRenderer

JButton button = (JButton)value;

Most probably "value" is null here. For testing create button as JButton button = new JButton("Button");

Let me know if that works.