Creating a better JTable

JTable looks a little rough around the edges straight out of the box. With a couple of tweaks, though, we can make it fit in better on the Mac (and Windows too).

Here’s a screen shot of a JTable that uses no auto-resize (the default on most platforms) with no customization:

So what’s the most glaring problem here? Well for one, the table header doesn’t extend to the scrollbar. Second, there isn’t a scroll pane corner set on the upper right corner (in a perfect world, the scroll pane corner would merge into the table header, but we’ll let that go for now!).

Below, I’ve set the empty table header space to the right of the right-most column (if there is any) to paint the table header background. I’ve also installed a scroll pane corner and added row striping for effect. Here’s what it looks like:

Not bad.

Below is the implementation. Note that I’ve done the striping in a custom JViewport because it’s much easier that way. Also, the selection intentionally doesn’t span the entire width of the viewport, as the native table selection doesn’t do this.

public class BetterJTable extends JTable {

    private static final Color EVEN_ROW_COLOR = new Color(241, 245, 250);
    private static final Color TABLE_GRID_COLOR = new Color(0xd9d9d9);

    private static final CellRendererPane CELL_RENDER_PANE = new CellRendererPane();

    public BetterJTable(TableModel dm) {
        super(dm);
        init();
    }

    private void init() {
        setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
        setTableHeader(createTableHeader());
        getTableHeader().setReorderingAllowed(false);
        setOpaque(false);
        setGridColor(TABLE_GRID_COLOR);
        setIntercellSpacing(new Dimension(0, 0));
        // turn off grid painting as we'll handle this manually in order to paint
        // grid lines over the entire viewport.
        setShowGrid(false);
    }

    /**
     * Creates a JTableHeader that paints the table header background to the right
     * of the right-most column if neccesasry.
     */
    private JTableHeader createTableHeader() {
        return new JTableHeader(getColumnModel()) {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                // if this JTableHEader is parented in a JViewport, then paint the
                // table header background to the right of the last column if
                // neccessary.
                JViewport viewport = (JViewport) table.getParent();
                if (viewport != null && table.getWidth() < viewport.getWidth()) {
                    int x = table.getWidth();
                    int width = viewport.getWidth() - table.getWidth();
                    paintHeader(g, getTable(), x, width);
                }
            }
        };
    }

    /**
     * Paints the given JTable's table default header background at given
     * x for the given width.
     */
    private static void paintHeader(Graphics g, JTable table, int x, int width) {
        TableCellRenderer renderer = table.getTableHeader().getDefaultRenderer();
        Component component = renderer.getTableCellRendererComponent(
                table, "", false, false, -1, 2);

        component.setBounds(0,0,width, table.getTableHeader().getHeight());

        ((JComponent)component).setOpaque(false);
        CELL_RENDER_PANE.paintComponent(g, component, null, x, 0,
                width, table.getTableHeader().getHeight(), true);
    }

    @Override
    public Component prepareRenderer(TableCellRenderer renderer, int row,
                                     int column) {
        Component component = super.prepareRenderer(renderer, row, column);
        // if the rendere is a JComponent and the given row isn't part of a
        // selection, make the renderer non-opaque so that striped rows show
        // through.
        if (component instanceof JComponent) {
            ((JComponent)component).setOpaque(getSelectionModel().isSelectedIndex(row));
        }
        return component;
    }

    // Stripe painting Viewport. //////////////////////////////////////////////

    /**
     * Creates a JViewport that draws a striped backgroud corresponding to the
     * row positions of the given JTable.
     */
    private static class StripedViewport extends JViewport {

        private final JTable fTable;

        public StripedViewport(JTable table) {
            fTable = table;
            setOpaque(false);
            initListeners();
        }

        private void initListeners() {
            // install a listener to cause the whole table to repaint when
            // a column is resized. we do this because the extended grid
            // lines may need to be repainted. this could be cleaned up,
            // but for now, it works fine.
            PropertyChangeListener listener = createTableColumnWidthListener();
            for (int i=0; i<fTable.getColumnModel().getColumnCount(); i++) {
                fTable.getColumnModel().getColumn(i).addPropertyChangeListener(listener);
            }
        }

        private PropertyChangeListener createTableColumnWidthListener() {
            return new PropertyChangeListener() {
                public void propertyChange(PropertyChangeEvent evt) {
                    repaint();
                }
            };
        }

        @Override
        protected void paintComponent(Graphics g) {
            paintStripedBackground(g);
            paintVerticalGridLines(g);
            super.paintComponent(g);
        }

        private void paintStripedBackground(Graphics g) {
            // get the row index at the top of the clip bounds (the first row
            // to paint).
            int rowAtPoint = fTable.rowAtPoint(g.getClipBounds().getLocation());
            // get the y coordinate of the first row to paint. if there are no
            // rows in the table, start painting at the top of the supplied
            // clipping bounds.
            int topY = rowAtPoint < 0
                    ? g.getClipBounds().y : fTable.getCellRect(rowAtPoint,0,true).y;

            // create a counter variable to hold the current row. if there are no
            // rows in the table, start the counter at 0.
            int currentRow = rowAtPoint < 0 ? 0 : rowAtPoint;
            while (topY < g.getClipBounds().y + g.getClipBounds().height) {
                int bottomY = topY + fTable.getRowHeight();
                g.setColor(getRowColor(currentRow));
                g.fillRect(g.getClipBounds().x, topY, g.getClipBounds().width, bottomY);
                topY = bottomY;
                currentRow ++;
            }
        }

        private Color getRowColor(int row) {
            return row % 2 == 0 ? EVEN_ROW_COLOR : getBackground();
        }

        private void paintVerticalGridLines(Graphics g) {
            // paint the column grid dividers for the non-existent rows.
            int x = 0;
            for (int i = 0; i < fTable.getColumnCount(); i++) {
                TableColumn column = fTable.getColumnModel().getColumn(i);
                // increase the x position by the width of the current column.
                x += column.getWidth();
                g.setColor(TABLE_GRID_COLOR);
                // draw the grid line (not sure what the -1 is for, but BasicTableUI
                // also does it.
                g.drawLine(x - 1, g.getClipBounds().y, x - 1, getHeight());
            }
        }
    }

    public static JScrollPane createStripedJScrollPane(JTable table) {
        JScrollPane scrollPane =  new JScrollPane(table);
        scrollPane.setViewport(new StripedViewport(table));
        scrollPane.getViewport().setView(table);
        scrollPane.setBorder(BorderFactory.createEmptyBorder());
        scrollPane.setCorner(JScrollPane.UPPER_RIGHT_CORNER,
                createCornerComponent(table));
        return scrollPane;
    }

    /**
     * Creates a component that paints the header background for use in a
     * JScrollPane corner.
     */
    private static JComponent createCornerComponent(final JTable table) {
        return new JComponent() {
            @Override
            protected void paintComponent(Graphics g) {
                paintHeader(g, table, 0, getWidth());
            }
        };
    }
}