Andrew E. Bruno
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Creating Sparklines with JFreeChart

Monday, January 15th, 2007

Sparklines are very small charts usually displayed along side some text and help quickly compare time series data. They are usually rendered without any axis, labels, or tick marks and appear as just a simple line. Sparklines were developed by Edward Tufte and further explained here.

JFreeChart does not have any built in classes for creating sparklines but are easily created by adjusting a few settings in the basic charting classes. Here's a few quick examples of some sparklines generated using JFreeChart:

Foo 90 Foo 90
Bar 34 Bar 34
Baz 54 Baz 54

To create sparklines using JFreeChart you just need to turn off the display of labels, tickmarks, lines, etc. on the domain/range axis as well as the XYPlot.

Here's a complete example:

import java.io.File;
import java.io.IOException;
import java.util.Calendar;
import java.util.Date;
import java.util.Random;

import org.jfree.chart.ChartUtilities;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.axis.DateAxis;
import org.jfree.chart.axis.DateTickUnit;
import org.jfree.chart.axis.NumberAxis;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.renderer.xy.StandardXYItemRenderer;
import org.jfree.data.time.Day;
import org.jfree.data.time.TimeSeries;
import org.jfree.data.time.TimeSeriesCollection;
import org.jfree.ui.RectangleInsets;

public class Sparkline {
    public static void main(String[] args) {
        TimeSeriesCollection dataSet = new TimeSeriesCollection();
        Day day = new Day();
        TimeSeries data = new TimeSeries("Sparkline", day.getClass());

        // XXX add real data here
        Random r = new Random();
        Calendar c = Calendar.getInstance();
        for(int i = 0; i < 100; i++) {
            int val = r.nextInt(100);
            if(val < 50)
                val += 50;
            c.add(Calendar.DATE, 7);
            Date date = c.getTime();
            data.add(new Day(date), val);
        }

        dataSet.addSeries(data);

        // The sparkline is created by setting a bunch of the visible properties
        // on the domain, range axis and the XYPlot to false
        DateAxis x = new DateAxis();
        x.setTickUnit(new DateTickUnit(DateTickUnit.MONTH, 1));
        x.setTickLabelsVisible(false);
        x.setTickMarksVisible(false);
        x.setAxisLineVisible(false);
        x.setNegativeArrowVisible(false);
        x.setPositiveArrowVisible(false);
        x.setVisible(false);

        NumberAxis y = new NumberAxis();
        y.setTickLabelsVisible(false);
        y.setTickMarksVisible(false);
        y.setAxisLineVisible(false);
        y.setNegativeArrowVisible(false);
        y.setPositiveArrowVisible(false);
        y.setVisible(false);

        XYPlot plot = new XYPlot();
        plot.setInsets(new RectangleInsets(-1, -1, 0, 0));
        plot.setDataset(dataSet);
        plot.setDomainAxis(x);
        plot.setDomainGridlinesVisible(false);
        plot.setDomainCrosshairVisible(false);
        plot.setRangeGridlinesVisible(false);
        plot.setRangeCrosshairVisible(false);
        plot.setRangeAxis(y);
        plot.setRenderer(new StandardXYItemRenderer(
                StandardXYItemRenderer.LINES));

        JFreeChart chart = new JFreeChart(null, JFreeChart.DEFAULT_TITLE_FONT,
                plot, false);
        chart.setBorderVisible(false);

        try {
            ChartUtilities.saveChartAsPNG(new File("sparkline.png"), chart,
                    100, 30);
        } catch(IOException e) {
            System.err.println("Failed to render chart as png: "
                    + e.getMessage());
            e.printStackTrace();
        }
    }
}

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