我尝试使用itext7将多个生成的pdf文件放入servlet的zip文件中，我已经成功地将一个pdf文件放入zip文件中，但没有更多。代码如下：

private void printMore(HttpServletRequest req, HttpServletResponse resp) throws SQLException {
        String masterPath = req.getServletContext().getRealPath("/assets/template/templateStatement.pdf");
        try (PdfReader reader = new PdfReader(masterPath);
             ZipOutputStream zipFile = new ZipOutputStream(resp.getOutputStream());
             PdfWriter writer = new PdfWriter(zipFile);
             PdfDocument pdf = new PdfDocument(reader, writer);
             Document doc = new Document(pdf)) {
            List<Student> studentList = getFactoryDAO().getStatementDAO().selectStudentHasBalance();
            for (Student student : studentList){
                // Generate PDF for the student
                PdfPage page = pdf.getPage(1);
                PdfCanvas canvas = new PdfCanvas(page);
                FontProgram fontProgram = FontProgramFactory.createFont();
                PdfFont font = PdfFontFactory.createFont(fontProgram, "utf-8", true);
                canvas.setFontAndSize(font, 10);
                canvas.beginText();
                canvas.setTextMatrix(178, 650); // student code
                canvas.showText(student.getS_Code());
                canvas.setTextMatrix(200, 610); // Date of Statement
                canvas.showText(new SimpleDateFormat("yyyy-MM-dd").format(new Date()));
                canvas.endText();
                float[] pointsWidth = {60f,120f,70f,70f};
                Table table = new Table(pointsWidth);
                table.setMarginTop(280);
                table.setMarginLeft(70);
                table.setFont(font);
                table.setFontSize(10);
                table.setTextAlignment(TextAlignment.CENTER);
                //Header Table
                table.addCell(new Cell().add("Date Inscription"));
                table.addCell(new Cell().add("Name"));
                table.addCell(new Cell().add("Fees"));
                table.addCell(new Cell().add("Observation"));
                //Detail Table
                table.addCell(new Cell().add(student.getTxnDate()));
                table.addCell(new Cell().add(student.getS_FullName));
                table.addCell(new Cell().add(student.getFees));
                table.addCell(new Cell().add(student.getObservation));
                doc.add(table);
                ZipEntry zipEntry = new ZipEntry(student.getS_Code() + "_" + student.getS_LName() + ".pdf");
                zipFile.putNextEntry(zipEntry);
                //zipFile.write(); Shall I use it?
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        resp.setHeader("Content-disposition","attachement; filename=test.zip");
        resp.setContentType("application/zip");
    }

我已经根据这篇文章和这篇文章，但不工作。我已经查看了更多类似的帖子，但是itext7的版本没有前面提到的pdfwriter.getinstance。我试过更多的东西，但都没能做得更好。
更新时间：
在enterman建议之后，我更新了它如下：

String masterPath = req.getServletContext().getRealPath("/assets/template/templateStatement.pdf");
        try (PdfReader reader = new PdfReader(masterPath);
             ZipOutputStream zipFile = new ZipOutputStream(resp.getOutputStream());
             PdfWriter writer = new PdfWriter(zipFile);
             PdfDocument pdf = new PdfDocument(reader, writer)
             ) {
            List<Student> studentList = getFactoryDAO().getStatementDAO().selectStudentHasBalance();
            for (Student student : studentList){
                try (Document doc = new Document(pdf)){
                       // Generate PDF for the student
                PdfPage page = pdf.getPage(1);
                PdfCanvas canvas = new PdfCanvas(page);
                FontProgram fontProgram = FontProgramFactory.createFont();
                PdfFont font = PdfFontFactory.createFont(fontProgram, "utf-8", true);
                canvas.setFontAndSize(font, 10);
                canvas.beginText();
                canvas.setTextMatrix(178, 650); // student code
                canvas.showText(student.getS_Code());
                canvas.setTextMatrix(200, 610); // Date of Statement
                canvas.showText(new SimpleDateFormat("yyyy-MM-dd").format(new Date()));
                canvas.endText();
                float[] pointsWidth = {60f,120f,70f,70f};
                Table table = new Table(pointsWidth);
                table.setMarginTop(280);
                table.setMarginLeft(70);
                table.setFont(font);
                table.setFontSize(10);
                table.setTextAlignment(TextAlignment.CENTER);
                //Header Table
                table.addCell(new Cell().add("Date Inscription"));
                table.addCell(new Cell().add("Name"));
                table.addCell(new Cell().add("Fees"));
                table.addCell(new Cell().add("Observation"));
                //Detail Table
                table.addCell(new Cell().add(student.getTxnDate()));
                table.addCell(new Cell().add(student.getS_FullName));
                table.addCell(new Cell().add(student.getFees));
                table.addCell(new Cell().add(student.getObservation));
                doc.add(table);
                ZipEntry zipEntry = new ZipEntry(student.getS_Code() + "_" + student.getS_LName() + ".pdf");
                zipFile.putNextEntry(zipEntry);
                //zipFile.write(); Shall I use it?
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        resp.setHeader("Content-disposition","attachement; filename=test.zip");
        resp.setContentType("application/zip");

但还是没有运气。
欢迎你的帮助。