Spring REST - create .zip file and send it to the client

Question

I want to create .zip file that contains my zipped files that I recieve from backend, and then send this file to the user. For 2 days I have been looking for the answer and

Answer 1

I am using REST Web Service of Spring Boot and I have designed the endpoints to always return ResponseEntity whether it is JSON or PDF or ZIP and I came up with the following solution which is partially inspired by denov's answer in this question as well as another question where I learned how to convert ZipOutputStream into byte[] in order to feed it to ResponseEntity as output of the endpoint.

Anyway, I created a simple utility class with two methods for pdf and zip file download

@Component
public class FileUtil {
    public BinaryOutputWrapper prepDownloadAsPDF(String filename) throws IOException {
        Path fileLocation = Paths.get(filename);
        byte[] data = Files.readAllBytes(fileLocation);

        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.parseMediaType("application/pdf"));
        String outputFilename = "output.pdf";
        headers.setContentDispositionFormData(outputFilename, outputFilename);
        headers.setCacheControl("must-revalidate, post-check=0, pre-check=0");

        return new BinaryOutputWrapper(data, headers); 
    }

    public BinaryOutputWrapper prepDownloadAsZIP(List<String> filenames) throws IOException {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.parseMediaType("application/zip"));
        String outputFilename = "output.zip";
        headers.setContentDispositionFormData(outputFilename, outputFilename);
        headers.setCacheControl("must-revalidate, post-check=0, pre-check=0");

        ByteArrayOutputStream byteOutputStream = new ByteArrayOutputStream();
        ZipOutputStream zipOutputStream = new ZipOutputStream(byteOutputStream);

        for(String filename: filenames) {
            File file = new File(filename); 
            zipOutputStream.putNextEntry(new ZipEntry(filename));           
            FileInputStream fileInputStream = new FileInputStream(file);
            IOUtils.copy(fileInputStream, zipOutputStream);
            fileInputStream.close();
            zipOutputStream.closeEntry();
        }           
        zipOutputStream.close();
        return new BinaryOutputWrapper(byteOutputStream.toByteArray(), headers); 
    }
}

And now the endpoint can easily return ResponseEntity<?> as shown below using the byte[] data and custom headers that is specifically tailored for pdf or zip.

@GetMapping("/somepath/pdf")
public ResponseEntity<?> generatePDF() {
    BinaryOutputWrapper output = new BinaryOutputWrapper(); 
    try {
        String inputFile = "sample.pdf"; 
        output = fileUtil.prepDownloadAsPDF(inputFile);
        //or invoke prepDownloadAsZIP(...) with a list of filenames
    } catch (IOException e) {
        e.printStackTrace();
        //Do something when exception is thrown
    } 
    return new ResponseEntity<>(output.getData(), output.getHeaders(), HttpStatus.OK); 
}

The BinaryOutputWrapper is a simple immutable POJO class I created with private byte[] data; and org.springframework.http.HttpHeaders headers; as fields in order to return both data and headers from utility method.

Answer 2

@RequestMapping(value="/zip", produces="application/zip")
public void zipFiles(HttpServletResponse response) throws IOException {

    //setting headers  
    response.setStatus(HttpServletResponse.SC_OK);
    response.addHeader("Content-Disposition", "attachment; filename=\"test.zip\"");

    ZipOutputStream zipOutputStream = new ZipOutputStream(response.getOutputStream());

    // create a list to add files to be zipped
    ArrayList<File> files = new ArrayList<>(2);
    files.add(new File("README.md"));

    // package files
    for (File file : files) {
        //new zip entry and copying inputstream with file to zipOutputStream, after all closing streams
        zipOutputStream.putNextEntry(new ZipEntry(file.getName()));
        FileInputStream fileInputStream = new FileInputStream(file);

        IOUtils.copy(fileInputStream, zipOutputStream);

        fileInputStream.close();
        zipOutputStream.closeEntry();
    }    

    zipOutputStream.close();
}

Answer 3

seems to be solved. I replaced:

response.setContentType("application/zip");

with:

@RequestMapping(value = "/zip", produces="application/zip")

And now I get clear, beautiful .zip file :)

If any of you have either better or faster proposition, or just want to give some advice, then go ahead, I am curious.

Answer 4

@RequestMapping(value="/zip", produces="application/zip")
public ResponseEntity<StreamingResponseBody> zipFiles() {
    return ResponseEntity
            .ok()
            .header("Content-Disposition", "attachment; filename=\"test.zip\"")
            .body(out -> {
                var zipOutputStream = new ZipOutputStream(out);

                // create a list to add files to be zipped
                ArrayList<File> files = new ArrayList<>(2);
                files.add(new File("README.md"));

                // package files
                for (File file : files) {
                    //new zip entry and copying inputstream with file to zipOutputStream, after all closing streams
                    zipOutputStream.putNextEntry(new ZipEntry(file.getName()));
                    FileInputStream fileInputStream = new FileInputStream(file);

                    IOUtils.copy(fileInputStream, zipOutputStream);

                    fileInputStream.close();
                    zipOutputStream.closeEntry();
                }

                zipOutputStream.close();
            });
}