Digital Magpie

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Dynamic Date Formatting

I’ve noticed a neat feature in Path Finder where it changes the date format used to display time stamps in the main table based on the width of the column. In RvSnoop I was allowing the user to set a preferred format as a configuration option, but this seems much better. It turns out that this is pretty easy to achieve in Java, just use the following class:

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public class DateCellRenderer extends DefaultTableCellRenderer {
    // Or load these from a user preference...
    private static final DateFormat[] dateFormats = {
    new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS"),
    new SimpleDateFormat("yy-MM-dd HH:mm:ss.SSS"),
    new SimpleDateFormat("MM/dd HH:mm:ss.SSS"),
    new SimpleDateFormat("HH:mm:ss.SSS"),
    new SimpleDateFormat("HH:mm:ss.SS"),
    new SimpleDateFormat("HH:mm:ss.S"),
    new SimpleDateFormat("HH:mm:ss"),
    new SimpleDateFormat("HH:mm") };
    private int currentWidth;
    private Font currentFont;
    private DateFormat currentFormat;
    private final Date date = new Date();
    public Component getTableCellRendererComponent(JTable table, Object value,
    boolean isSelected, boolean hasFocus, int row, int col) {
        DateFormat format = getFormat(table.getColumnModel().getColumn(col).getWidth(), table);
        String displayed = value != null ? format.format((Date) value) : "";
        return super.getTableCellRendererComponent(table, displayed, isSelected, hasFocus, row, col);
    }
    private DateFormat getFormat(int width, JTable table) {
        Font font = table.getFont();
        if (currentWidth == width && currentFormat != null && font.equals(currentFont)) {
            return currentFormat;
        }
        currentWidth = width;
        currentFont = font;
        FontMetrics metrics = table.getFontMetrics(font);
        date.setTime(System.currentTimeMillis())
        for (DateFormat df : dateFormats) {
            if (metrics.stringWidth(df.format(date)) < width) {
                currentFormat = df;
                return df;
                }
            }
        }
        currentFormat = dateFormats[dateFormats.length - 1];
        return currentFormat;
    }
}

You will need to register it with your JTable via myTable.getColumnModel().getColumn(0).setCellRenderer(myRenderer); and away you go. You can have more or less format options by altering the static array in the class.