如何在iText5中绘制圆的阴影

import com.itextpdf.text.Document;
import com.itextpdf.text.DocumentException;
import com.itextpdf.text.pdf.PdfContentByte;
import com.itextpdf.text.pdf.PdfWriter;

import java.io.FileOutputStream;
import java.io.IOException;

public class DrawCircleWithShadow {
    public static void main(String[] args) {
        Document document = new Document();
        try {
            PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream("circle_with_shadow.pdf"));
            document.open();

            PdfContentByte canvas = writer.getDirectContent();

            // 设置阴影参数
            float shadowOffsetX = 2;
            float shadowOffsetY = 2;
            float shadowBlur = 3;
            canvas.setGState(new PdfGState().setFillOpacity(0.5f));

            // 绘制阴影
            canvas.saveState();
            canvas.setColorFill(BaseColor.GRAY);
            canvas.circle(297.5f, 421, 50);
            canvas.fill();
            canvas.restoreState();

            // 绘制圆
            canvas.saveState();
            canvas.setColorFill(BaseColor.BLUE);
            canvas.circle(297.5f, 421, 50);
            canvas.fill();
            canvas.restoreState();

            document.close();
        } catch (DocumentException | IOException e) {
            e.printStackTrace();
        }
    }
}