Java uses itext5 implementation to generate multiple PDFs and merge

    /**
      * Query data based on id
      * @param id Data id
      * @return
      */
    private Map<String, String> queryEntityDataById(String id) {
        //Query based on id        Box entity = (id);

        Map<String, String> data = new HashMap<String, String>();
        //Show content        //id
        ("id", ());
        //Dynamic generation of yymmddhh format of the current time        DateTimeFormatter formatter = ("yyMMddHH");
        String currentDate = ().format(formatter);
        ("date", currentDate);

        //QR code content        ("imsi", ());
        ("imei", ());

        String type = ();
        if (type == null || ()) {
            type = "A";
        }
        ("type", type);
        return data;
    }

    // Generate PDF based on the data    private void generatePdfForData(Map<String, String> data, ByteArrayOutputStream outputStream) throws Exception {
        // Load the PDF template
        InputStream templateStream = getClass().getResourceAsStream("/template/");
        PdfReader reader = new PdfReader(templateStream);
        PdfStamper stamper = new PdfStamper(reader, outputStream);

        AcroFields form = ();
        String fontPath =  + "font" +  + "";
        BaseFont bfChinese = (fontPath, BaseFont.IDENTITY_H, );
        Map<String, > fields = ();
        for (String k : ()) {
            (k, "textfont", bfChinese, null);
            (k, "textsize", ("55"), null);
            (k, "textstyle", , null);
            (k, "textalign", Element.ALIGN_MIDDLE, null);
        }
        //Reset the font size of the special text box        ("$serialnumber$", "textsize", ("40"), null);
        //Tag content        //ID
        ("$id$", ("id"));
        //date        ("$date$", ("date"));

        //QR code        String qrContent = (
                        "ID:%s\n" +
                        "IMSI:%s\n" +
                        "IMEI:%s\n" +
                        "type:%s",
                ("id"), ("imsi"), ("imei"),("type"));
        PdfContentByte cb = (1);
        generateQRcode(qrContent, cb);
        (true);
        ();
        ();
    }

    /**
      * Generate pdf in batches and merge according to ID
      * @param ids ids collection
      * @return Direct access to pdf stream file
      */
    @GetMapping("/generateMergePdfStream")
    public ResponseEntity<ByteArrayResource> generateMergePdfStream(@RequestParam String ids) {
        long startTime = ();
        ("Start to generate PDF: " + startTime);
        try {
            String[] idArray = (",");
            ByteArrayOutputStream mergedOutputStream = new ByteArrayOutputStream();
            Document mergedDocument = new Document();
            PdfSmartCopy copy = new PdfSmartCopy(mergedDocument, mergedOutputStream);
            ();

            for (String id : idArray) {
                Map<String, String> data = queryEntityDataById(());

                ByteArrayOutputStream pdfOutputStream = new ByteArrayOutputStream();
                generatePdfForData(data, pdfOutputStream);

                ("The generated PDF file size: " + ());

                PdfReader reader = new PdfReader(new ByteArrayInputStream(()));
                (reader);
                ();
                ();
            }

            ();

            ByteArrayResource resource = new ByteArrayResource(());

            HttpHeaders headers = new HttpHeaders();
            ("Content-Disposition", "inline; filename=");

            long generationEnd = ();
            ("PDF generation and merge completed, total time taken: " + (generationEnd - startTime) + "Milliseconds");

            return ()
                    .headers(headers)
                    .contentType(MediaType.APPLICATION_PDF)
                    .body(resource);

        } catch (Exception e) {
            ();
            return (500).build();
        }
    }

#Accessing files of the same level at the jar package location can directly access the file name under http://IP:port/files-locations=file:./files/

    /**
      * Generate the merged pdf file and save it to the server
      * The following needs to configure -locations=file:./files/
      * folder directory where jar package runs
      * @param ids ids collection
      * @return Direct access http://IP:Port/*.pdf
      */
    @GetMapping("/generateentityLogPdf")
    public ResponseEntity generateMergeSavePdf(@RequestParam String ids, HttpServletRequest request) {
        try {
            // Split ids            String[] idArray = (",");

            // Output stream            ByteArrayOutputStream mergedOutputStream = new ByteArrayOutputStream();
            Document mergedDocument = new Document();
            PdfCopy copy = new PdfCopy(mergedDocument, mergedOutputStream);
            ();

            for (String id : idArray) {
                //Query the required data for pdf based on id                Map<String, String> data = queryEntityDataById(());

                // Generate pdf data stream based on id                ByteArrayOutputStream pdfOutputStream = new ByteArrayOutputStream();
                generatePdfForData(data, pdfOutputStream);

                // The generated pdf data stream                PdfReader reader = new PdfReader(new ByteArrayInputStream(()));
                (reader);
                ();
            }

            ();

            //Save file path            String currentDateDir = ().format(("yyyyMMdd"));
            // Get the files directory path in the running directory            String filePath = ("") +  + "files" +  + currentDateDir;
            File directory = new File(filePath);

            // Check whether the directory exists. If it does not exist, create it            if (!()) {
                ();
            }

            // Save the file name            Random random = new Random();
            int randomNumber = (1000);
            String fileName = () + "_" + randomNumber + ".pdf";

            File file = new File(directory, fileName);
            try (FileOutputStream fos = new FileOutputStream(file)) {
                (());
                ();
                ("File saving successfully:" + ());
            } catch (IOException e) {
                ();
            }
            //Return the URL that directly accesses PDF            String ip = ();
            int port = ();
            String fileUrl = "http://" + ip + ":" + port + "/" + currentDateDir + "/" + fileName;
            return (fileUrl);
        } catch (Exception e) {
            ();
            return (500).build();
        }
    }