How to send PDF file on response-CodePudding

I'm trying to write a web app that converts images to PDF file. The user sends a couple of images (JPEG, PNG) and should receive and download a PDF file.

The main problem, for now, is that I don't know how to return the PDF file back to the client.

Here is my controller:

    @PostMapping(path = "/upload",
            consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    public void uploadFiles(@RequestParam("files") MultipartFile[] files) throws IOException {
        imageToPdfConversionService.convert(files);
    }

This is the service that converts images to PDF file (here I'm using itextpdf library):

public void convert(MultipartFile[] files) throws IOException {

        List<ImageData> imagesData = Arrays.stream(files)
                .map(file -> {
                    try {
                        return ImageDataFactory.create(file.getBytes());
                    } catch (IOException e) {
                        throw new RuntimeException(e);
                    }
                })
                .collect(Collectors.toList());

//        PdfDocument pdfDocument = new PdfDocument(new PdfWriter("ImageToPdf.pdf"));
        FileOutputStream fileOutputStream = new FileOutputStream("letspdf-server/src/main/resources/documents/file.pdf");
        PdfDocument pdfDocument = new PdfDocument(new PdfWriter(fileOutputStream));

        Document document = new Document(pdfDocument);

        for (ImageData image : imagesData) {
            Image img = new Image(image);
            img.setWidth(pdfDocument.getDefaultPageSize().getWidth() - 50);
            img.setAutoScaleHeight(true);
            document.add(img);
            pdfDocument.addNewPage();
        }
        pdfDocument.close();
    }

Also, maybe store a PDF file somewhere and create a 'Download' button on the client-side when a file is generated to download the file from storage?

CodePudding user response：

So first of all you need to change your api to return ResponseEntity and convert your resulted pdf into byte array. I'll attach a code snippet as an example

public static ResponseEntity<Resource> makeResponse(byte[] file, String filename, MultiValueMap<String, String> customHeaders) {
    MediaType mediaType = MediaType.APPLICATION_OCTET_STREAM;
    HttpHeaders headers = new HttpHeaders();
    if (StringUtils.isNotEmpty(filename)) {
        try {
            mediaType = MediaType.valueOf(MIME_TYPES.detect(filename));
        } catch (Exception var6) {
        }

        ContentDisposition contentDisposition = ContentDisposition.builder("attachment").filename(filename, StandardCharsets.UTF_8).build();
        headers.setAccessControlExposeHeaders(ACCESS_CONTROL_EXPOSE_HEADERS);
        headers.setContentDisposition(contentDisposition);
    }

    if (customHeaders != null && !customHeaders.isEmpty()) {
        headers.addAll(customHeaders);
    }

    ByteArrayResource body = null;
    if (file != null) {
        body = new ByteArrayResource(file);
    }

    return ((BodyBuilder)ResponseEntity.ok().headers(headers)).contentType(mediaType).body(body);
}