在使用Apache poi生成.docx时，如何为页脚添加间距？

XWPFDocument document = new XWPFDocument();

XWPFHeaderFooterPolicy headerFooterPolicy = document.getHeaderFooterPolicy();
if (headerFooterPolicy == null) {
    headerFooterPolicy = document.createHeaderFooterPolicy();
}

XWPFFooter footer = headerFooterPolicy.createFooter(XWPFHeaderFooterPolicy.DEFAULT);

XWPFParagraph paragraph = footer.createParagraph();

XWPFRun run = paragraph.createRun();
run.setText("页脚内容");

CTP ctp = paragraph.getCTP();
CTPPr ctpPr = ctp.getPPr();
if (ctpPr == null) {
    ctpPr = ctp.addNewPPr();
}
CTSpacing spacing = ctpPr.isSetSpacing() ? ctpPr.getSpacing() : ctpPr.addNewSpacing();
spacing.setAfter(BigInteger.valueOf(240)); // 设置页脚的下边距，单位为磅（1英寸=72磅）

FileOutputStream out = new FileOutputStream("output.docx");
document.write(out);
out.close();
document.close();