Download Large file from server using REST template Java Spring MVC

As @bernie mentioned you can use WebClient to achieve this:

public Flux<DataBuffer> downloadFileUrl( ) throws IOException { WebClient webClient = WebClient.create(); // Request service to get file data return Flux<DataBuffer> fileDataStream = webClient.get() .uri( this.fileUrl ) .accept( MediaType.APPLICATION_OCTET_STREAM ) .retrieve() .bodyToFlux( DataBuffer.class ); } @GetMapping( produces = MediaType.APPLICATION_OCTET_STREAM_VALUE ) public void downloadFile( HttpServletResponse response ) throws IOException { Flux<DataBuffer> dataStream = this.downloadFileUrl( ); // Streams the stream from response instead of loading it all in memory DataBufferUtils.write( dataStream, response.getOutputStream() ) .map( DataBufferUtils::release ) .blockLast(); } 

You can still use WebClient even if you don't have Reactive Server stack - Rossen Stoyanchev (a member of Spring Framework team) explains it quite well in the Guide to "Reactive" for Spring MVC Developers presentation. During this presentation, Rossen Stoyanchev mentioned that they thought about deprecating RestTemplate, but they have decided to postpone it after all, but it may still happen in the future!

The main disadvantage of using WebClient so far it's a quite steep learning curve (reactive programming), but I think there is no way to avoid in the future, so better to take a look on it sooner than latter.

This prevents loading the entire request into memory.

SimpleClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory(); requestFactory.setBufferRequestBody(false); RestTemplate rest = new RestTemplate(requestFactory); 

For java.lang.OutOfMemoryError: Java heap space can be solved adding more memory to the JVM:

-Xmxn Specifies the maximum size, in bytes, of the memory allocation pool. This value must a multiple of 1024 greater than 2 MB. Append the letter k or K to indicate kilobytes, or m or M to indicate megabytes. The default value is chosen at runtime based on system configuration.

For server deployments, -Xms and -Xmx are often set to the same value. See Garbage Collector Ergonomics at http://docs.oracle.com/javase/7/docs/technotes/guides/vm/gc-ergonomics.html

Examples:

-Xmx83886080
-Xmx81920k
-Xmx80m

Probably the problem you have is not strictly related to the request you are trying to execute (download large file) but the memory allocated for the process is not enough.

A better version of above correct answer could be the below code. This method will send download request to another application or service acting as actual source of truth for downloaded information.

public void download(HttpServletRequest req, HttpServletResponse res, String url) throws ResourceAccessException, GenericException { try { logger.info("url::" + url); if (restTemplate == null) logger.info("******* rest template is null***********************"); RequestCallback requestCallback = request -> request.getHeaders() .setAccept(Arrays.asList(MediaType.APPLICATION_OCTET_STREAM, MediaType.ALL)); // Streams the response instead of loading it all in memory ResponseExtractor<ResponseEntity<InputStream>> responseExtractor = response -> { String contentDisposition = response.getHeaders().getFirst("Content-Disposition"); if (contentDisposition != null) { // Temporary location for files that will be downloaded from micro service and // act as final source of download to user String filePath = "/home/devuser/fileupload/download_temp/" + contentDisposition.split("=")[1]; Path path = Paths.get(filePath); Files.copy(response.getBody(), path, StandardCopyOption.REPLACE_EXISTING); // Create a new input stream from temporary location and use it for downloading InputStream inputStream = new FileInputStream(filePath); String type = req.getServletContext().getMimeType(filePath); res.setHeader("Content-Disposition", "attachment; filename=" + contentDisposition.split("=")[1]); res.setHeader("Content-Type", type); byte[] outputBytes = new byte[100]; OutputStream os = res.getOutputStream(); int read = 0; while ((read = inputStream.read(outputBytes)) != -1) { os.write(outputBytes, 0, read); } os.flush(); os.close(); inputStream.close(); } return null; }; restTemplate.execute(url, HttpMethod.GET, requestCallback, responseExtractor); } catch (Exception e) { logger.info(e.toString()); throw e; } } 

You should use multipart file attachment, so the file stream isn't load into memory. In this example, I use a rest service implemented with Apache CXF.

... import org.apache.cxf.jaxrs.ext.multipart.Attachment; ... @Override @Path("/put") @Consumes("multipart/form-data") @Produces({ "application/json" }) @POST public SyncResponseDTO put( List<Attachment> attachments) { SyncResponseDTO response = new SyncResponseDTO(); try { for (Attachment attr : attachments) { log.debug("get input filestream: " + new Date()); InputStream is = attr.getDataHandler().getInputStream();