How to offer a file compressed as download via spring @RestController?

Question

I have a servlet that offers a CSV file for download:

@RestController 
@RequestMapping("/")
public class FileController {

    @RequestMapping(value = "/export", method = RequestMethod.GET)
    public FileSystemResource getFile() {
        return new FileSystemResource("c:\file.csv"); 
    }
}

This works just fine.

Question: how can I offer this file as compressed file? (zip, gzip, tar doesn't matter)?

Answer 1

Based on the solution here (for a plain Servlet), you can also do the same with a Spring MVC based controller.

@RequestMapping(value = "/export", method = RequestMethod.GET)
public void getFile(OutputStream out) {
    FileSystemResource resource = new FileSystemResource("c:\file.csv"); 
    try (ZipOutputStream zippedOut = new ZipOutputStream(out)) {
        ZipEntry e = new ZipEntry(resource.getName());
        // Configure the zip entry, the properties of the file
        e.setSize(resource.contentLength());
        e.setTime(System.currentTimeMillis());
        // etc.
        zippedOut.putNextEntry(e);
        // And the content of the resource:
        StreamUtils.copy(resource.getInputStream(), zippedOut);
        zippedOut.closeEntry();
        zippedOut.finish();
    } catch (Exception e) {
        // Do something with Exception
    }        
}

You created a ZipOutputStream based on the responses OutputStream (which you can simply have injected into the method). Then create an entry for the zipped out stream and write it.

Instead of the OutputStream you could also wire the HttpServletResponse so that you would be able to set the name of the file and the content type.

@RequestMapping(value = "/export", method = RequestMethod.GET)
public void getFile(HttpServletResponse response) {
    FileSystemResource resource = new FileSystemResource("c:\file.csv"); 
    response.setContentType("application/zip");
    response.setHeader("Content-Disposition", "attachment; filename=file.zip");

    try (ZipOutputStream zippedOut = new ZipOutputStream(response.getOutputStream())) {
        ZipEntry e = new ZipEntry(resource.getName());
        // Configure the zip entry, the properties of the file
        e.setSize(resource.contentLength());
        e.setTime(System.currentTimeMillis());
        // etc.
        zippedOut.putNextEntry(e);
        // And the content of the resource:
        StreamUtils.copy(resource.getInputStream(), zippedOut);
        zippedOut.closeEntry();
        zippedOut.finish();
    } catch (Exception e) {
        // Do something with Exception
    }        
}