如何确定使用iText选择了哪个单选按钮？

import com.itextpdf.text.Document;
import com.itextpdf.text.DocumentException;
import com.itextpdf.text.pdf.*;

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

public class RadioButtonExample {
    public static void main(String[] args) {
        try {
            // 创建一个空白的PDF文档
            Document document = new Document();
            PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream("example.pdf"));
            document.open();

            // 创建单选按钮组
            PdfFormField radioGroup = PdfFormField.createRadioButton(writer, true);
            radioGroup.setFieldName("radioGroup");

            // 添加单选按钮到表单
            PdfFormField radioButton1 = PdfFormField.createEmpty(writer);
            radioButton1.setFieldName("radioButton1");
            radioButton1.setValueAsName("value1");
            radioButton1.setAppearance(PdfAnnotation.APPEARANCE_NORMAL, "Off", PdfAppearance.createRadioButton(writer, 10, 10, 10, 10, "Off"));
            radioGroup.addKid(radioButton1);

            PdfFormField radioButton2 = PdfFormField.createEmpty(writer);
            radioButton2.setFieldName("radioButton2");
            radioButton2.setValueAsName("value2");
            radioButton2.setAppearance(PdfAnnotation.APPEARANCE_NORMAL, "Off", PdfAppearance.createRadioButton(writer, 30, 10, 10, 10, "Off"));
            radioGroup.addKid(radioButton2);

            // 将单选按钮组添加到文档
            writer.addAnnotation(radioGroup);

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