net.sf.jasperreports.engine.JRRuntimeException: Could not create chart customizer instance.
Caused by: java.lang.ClassCastException: org.jfree.chart.renderer.category.BarRenderer cannot be cast to net.sf.jasperreports.engine.JRChartCustomizer

public class MyCustomizer extends JRAbstractChartCustomizer {
    public void customize(JFreeChart chart, JRChart jasperChart) {
        if (chart.getPlot() instanceof CategoryPlot) {
            CategoryPlot plot = (CategoryPlot) chart.getPlot();
            plot.setRenderer(new BarRenderer());
        }
    }
}