Image as category label in iReport chart

Question

I'm trying to create a bar chart with images for the category labels (x-axis labels). For the default bar chart, the result of the category expression is used as the label (and must be a String). How can I customize this to show an image instead? I've written a scriptlet to populate a variable with BufferedImages, now I just need a way to use them. Can I do this with a chart customizer class? Is there an easier/better way?

Answer 1

As you said, you can do that by own customizer class. Here is a simple example which can be enhanced by your needs:

@Slf4j 
public class CategoryAxisWithImagesCustomizer extends JRAbstractChartCustomizer {
    public class CategoryAxisWithImages extends CategoryAxis {
        public CategoryAxisWithImages(String label) {
            super(label);
        }

        @Override
        protected Rectangle2D getLabelEnclosure(Graphics2D g2, RectangleEdge edge) {
            // enter max width and height of your images or you can do it dynamically
            return new Rectangle2D.Double(0, 0, 32, 32);
        }

        @Override
        protected AxisState drawCategoryLabels(Graphics2D g2, Rectangle2D plotArea, Rectangle2D dataArea, RectangleEdge edge, AxisState state, PlotRenderingInfo plotState) {
            if (!isTickLabelsVisible()) {
                return state;
            }

            List ticks = refreshTicks(g2, state, plotArea, edge);
            state.setTicks(ticks);
            for (int i = 0; i < ticks.size(); i++) {
                double x = getCategoryMiddle(i, ticks.size(), dataArea, edge);
                double y = state.getCursor() + getCategoryLabelPositionOffset();

                int value = (int) ((CategoryPlot) getPlot()).getDataset().getColumnKey(i);
                String imagePath = "logo_" + value + ".png";
                try {
                    InputStream imageStream = getClass().getResourceAsStream(imagePath);
                    // you can of course load images using different way - here I'm using index value from the dataset
                    BufferedImage image = ImageIO.read(imageStream);
                    g2.drawImage(image, (int) (x - image.getWidth() / 2d), (int) (y), image.getWidth(), image.getHeight(), Color.black, null);
                } catch (IOException e) {
                    log.error("Cannot load image {}", imagePath);
                }
            }
            state.cursorDown(state.getMax() + getCategoryLabelPositionOffset());
            return state;
        }
    }

    @Override
    public void customize(JFreeChart chart, JRChart jasperChart) {
        CategoryPlot plot = chart.getCategoryPlot();
        CategoryAxis categoryAxis = new CategoryAxisWithImages(plot.getDomainAxis().getLabel());
        plot.setDomainAxis(categoryAxis);
    }
}

In JasperReport JRXML you can register that customizer class like this:

    <barChart>
        <chart customizerClass="cz.trask.experiment.jr.CategoryAxisWithImagesCustomizer"
               isShowLegend="false">
            <reportElement x="0" y="0" width="550" height="348" uuid="a2cbb6b5-a76d-469b-8e8e-daa533260f20"/>
            <chartTitle/>
            <chartSubtitle/>
            <chartLegend/>
        </chart>
        ...
    </barChart>

And the result of my example is: