Downloading a file from Spring controllers

java

spring

file-downloading

rest-api

byNikita Barsukov·Oct 5, 2024

For swift file downloads, use Spring's ResponseEntity in your controller. Deliver a ResponseEntity<Resource> with the Content-Disposition header set to "attachment". Use MediaType to specify the MIME type, ensuring the browser treats the file appropriately.

@GetMapping("/download")
public ResponseEntity<Resource> downloadFile() {
    Resource file = new FileSystemResource("/path/to/myfile.txt");

    return ResponseEntity.ok()
            .contentType(MediaType.APPLICATION_OCTET_STREAM)
            .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + file.getFilename() + "\"")
            .body(file);
}

Replace "/path/to/myfile.txt" with your specific file path to make this code snippet ready for use. This sends your file as a downloadable link, named by its original name on the server.

Broadening the Horizon

Serving specific file paths

When working with fluctuating file paths, @PathVariable comes to the rescue:

@GetMapping("/download/{filename:.+}")
public ResponseEntity<Resource> downloadFile(@PathVariable String filename) {
    Resource file = new FileSystemResource("uploads/" + filename);
    // Here be dragons 🐉! Make sure the path is safe!
    
    return ResponseEntity.ok()
        .contentType(MediaType.parseMediaType("application/octet-stream"))
        .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + file.getFilename() + "\"")
        .body(file);
}

Handling Errors like a Boss

Graceful error handling is essential, use @ControllerAdvice for sweeping handling or try-catch blocks for localized issues:

@GetMapping("/download/{filename:.+}")
public ResponseEntity<Resource> downloadFile(@PathVariable String filename, HttpServletResponse response) {
    try {
        Resource file = new FileSystemResource("uploads/" + filename);
        // Performance art: file juggling 🤹‍♀️, and check to see if it landed!
        
        return ResponseEntity.ok()
            .contentType(MediaType.APPLICATION_OCTET_STREAM)
            .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + file.getFilename() + "\"")
            .body(file);
    } catch (Exception e) {
        // Whoops! Error alert 🚨. Log and retreat.
        response.setStatus(HttpServletResponse.SC_NOT_FOUND);
        return ResponseEntity.status(HttpStatus.NOT_FOUND).build();
    }
}

Storing Large Files in the Cloud

When streaming huge files, don't bog down memory. Instead, float on cloud 9 with StreamResource and ResourceHttpMessageConverter:

@GetMapping("/download/{filename:.+}")
public ResponseEntity<Resource> downloadFileStream(@PathVariable String filename) throws IOException {
    Path path = Paths.get("uploads/" + filename);
    InputStreamResource resource = new InputStreamResource(Files.newInputStream(path));

    // Remember, it's not the size that matters, it's how you use it 😉
    return ResponseEntity.ok()
        .contentLength(Files.size(path))
        .contentType(MediaType.APPLICATION_OCTET_STREAM)
        .body(resource);
}

Streamlining with Apache Commons IO

Apache Commons IO to the rescue for an elegant way to shuttle bytes between streams:

@GetMapping("/download/{filename:.+}")
public void downloadWithCommonsIO(@PathVariable String filename, HttpServletResponse response) throws IOException {
    File file = new File("uploads/" + filename); // so fresh and so clean 🛀
    response.setContentType("application/octet-stream");
    response.setHeader("Content-Disposition", "attachment; filename=\"" + file.getName() + "\"");
    
    try (InputStream is = new FileInputStream(file);
         OutputStream os = response.getOutputStream()) {
        IOUtils.copy(is, os); // copy-paste like a pro 😎
        response.flushBuffer();
    }
    // Watch out for those IOExceptions! They bite 🦈
}

Advanced Solutions

Custom PDF Generation

To serve PDF files, iText might be your knight in shining armor:

@GetMapping("/download/pdf")
public ResponseEntity<InputStreamResource> downloadPdf() throws IOException {
    ByteArrayOutputStream outputStream = createPdf(); // Masterpiece generator here 🖼️
    ByteArrayInputStream inputStream = new ByteArrayInputStream(outputStream.toByteArray());

    HttpHeaders headers = new HttpHeaders();
    headers.add("Content-Disposition", "inline; filename=myfile.pdf");

    return ResponseEntity
            .ok()
            .headers(headers)
            .contentType(MediaType.APPLICATION_PDF)
            .body(new InputStreamResource(inputStream));
}

Auto-detect mime type

Leverage Spring's superpower to auto-detect mime type:

// It's a bird 🦅, it's a plane ✈️, no it's mime type detection!
@GetMapping("/download/{filename:.+}")
public ResponseEntity<Resource> downloadFileAutoMimeType(@PathVariable String filename) throws IOException {
    Resource file = new FileSystemResource("uploads/" + filename);
    String mimeType = ServletUriComponentsBuilder.fromCurrentContextPath()
                            .build()
                            .getServletContext()
                            .getMimeType(file.getFile().getAbsolutePath());

    return ResponseEntity.ok()
        .contentType(MediaType.parseMediaType(mimeType)) // apply mime type like a boss 😎
        .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + file.getFilename() + "\"")
        .body(file);
}

Template-based file generation

For the elegant solution of template-based PDFs, Freemarker synergizes well with iText:

@GetMapping("/download/templatePdf") // Keep your design 👗 to your PDFs.
public ResponseEntity<InputStreamResource> downloadTemplatePdf(@RequestParam String orderId) throws IOException {
    ByteArrayInputStream byteArrayInputStream = pdfService.generatePdfFromTemplate(orderId); // Craftsmanship included

    HttpHeaders headers = new HttpHeaders();
    headers.add(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=order-" + orderId + ".pdf");

    return ResponseEntity
            .ok()
            .headers(headers)
            .contentType(MediaType.APPLICATION_PDF)
            .body(new InputStreamResource(byteArrayInputStream));
}