Decorating a JFreeChart

Question

I would like to decorate all my generated JFreeCharts with a timestamp in the corner. Is there a way within the JFreeChart framework to draw on the image after the chart has been generated?

EDIT: Note that these charts are being generated in a background thread and distributed via a servlet, so there is no GUI and I can't just display the timestamp on a separate component.

Answer 1

After dinking around with it some more, I found a solution that lets you draw arbitrarily on the image after JFreeChart is done with it, so I'll post it here for posterity. In my case, I was writing the chart to an OutputStream, so my code looked something like this:

BufferedImage chartImage = chart.createBufferedImage(width, height, null);
Graphics2D g = (Graphics2D) chartImage.getGraphics();
/* arbitrary drawing happens here */
EncoderUtil.writeBufferedImage(chartImage, ImageFormat.PNG, outputStream);

Answer 2

One approach would be to subclass ChartPanel and override the paint(Graphics) method to first chain to super.paint(Graphics) and subsequently render the additional text on top of the chart.

This feels a bit hacky to me though and I'd personally favour simply adding the ChartPanel to another container JPanel along with a JLabel representing the timestamp.

Answer 3

Take a look at this forum post here:

http://www.jfree.org/phpBB2/viewtopic.php?f=3&t=27939

That uses an ImageIcon as a watermark:

ImageIcon icon = new ImageIcon(new URL(watermarkUrl));
Image image = icon.getImage();
chart.setBackgroundImage(image);
chart.setBackgroundImageAlignment(Align.CENTER);
chart.getPlot().setBackgroundAlpha(0.2f);

Answer 4

The addSubtitle() method of org.jfree.chart.JFreeChart may be a suitable alternative.

Answer 5

In my Experience the best way to add custom information to JFreeChart is: - Instantiate a BufferedImage of the same type of the chart; - draw on the BufferedImage ; - add the image to the current Plot, by using an XYImageAnnotation.

This is a guideline for the code:

// retrieve image type and create another BufferedImage
int imgType = chart.createBufferedImage(1,1).getType();
BufferedImage bimg = new BufferedImage(width, height, bimg.getType);

// here you can draw inside the image ( relative x & y  )
Graphics2D g2 = (Graphics2D) bimg.getGraphics();
g2.drawString("Hello, JFreeChart " + timestamp, posX, posY );

// instantiate the image annotation, then add to the plot
XYImageAnnotation a = new XYImageAnnotation( x, y, bimg, RectangleAnchor.LEFT );
chart.getPlot().addAnnotation( a );