java将文字内容写入pdf并提供下载链接

public ResponseEntity<byte[]> exportResource(int lessonPlanId) {
        try {
            // 获取课程计划
            LessonPlan lessonPlan = lessonPlanService.selectById(lessonPlanId);
            if (lessonPlan == null) {
                log.error("课程计划不存在: lessonPlanId={}", lessonPlanId);
                return ResponseEntity.badRequest().body(null); // 课程计划不存在
            }

            // 记录内容
            log.info("课程计划标题: {}", lessonPlan.getTitle());
            log.info("课程计划内容: {}", lessonPlan.getContent());

            // 创建 PDF 文件流
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            PdfWriter writer = new PdfWriter(baos);
            PdfDocument pdf = new PdfDocument(writer);
            Document document = new Document(pdf);

            // 设置支持中文的字体
            PdfFont font = PdfFontFactory.createFont("STSong-Light", "UniGB-UCS2-H");
            document.setFont(font);

            // 添加课程计划标题和内容
            document.add(new Paragraph("课程计划: " + lessonPlan.getTitle()).setFont(font));
            document.add(new Paragraph("内容: " + lessonPlan.getContent()).setFont(font));

            // 关闭文档
            document.close();

            // 设置 HTTP 头
            HttpHeaders headers = new HttpHeaders();
            headers.setContentType(MediaType.APPLICATION_PDF);
            headers.setContentDispositionFormData("attachment", "lesson_plan_" + lessonPlanId + ".pdf");

            // 返回文件流
            return ResponseEntity.ok()
                    .headers(headers)
                    .body(baos.toByteArray());

        } catch (Exception e) {
            log.error("生成 PDF 失败: lessonPlanId={}, 错误: {}", lessonPlanId, e.getMessage());
            e.printStackTrace();
            return ResponseEntity.status(500).body(null); // 服务器错误
        }
    }