Rest template read response as stream and pass to spring controller(Get InputStream with rest Template)

Question

I have a url which download the large size zip file.It returns the response as stream.though file size is large first it returns 200(HTTPSTATUK.OK) and continues download.

I have to implement a new spring controller which call the above url through rest template.I have to read the response returned by rest template and pass to controller.initially I have implemented in below way

     @GetMapping("/export/downloadFile")
        public ResponseEntity<byte[]> downloadData(Model model,
                                                       @ModelAttribute(EXCEPTION_COLLECTOR) ExceptionCollector exceptionCollector,
                                                       @RequestParam("userName") String userName,
                                                       @RequestParam("startDate") Date startDate,
                                                       @RequestParam("endDate") Date endDate,
                                                       @RequestParam("reason") String reason) {

   URI uri = /building url here/;
    
    return restTemplate.exchange(uri, HttpMethod.GET, new HttpEntity<>(httpHeaders), byte[].class);
    
    }

since I am using ResponseEntity<byte[]> , rest template waits till entire file loaded into memory.so very frequently I am getting socket timeout issue.

Do we have way to read the response as stream and return to controller.

I found few things about restTemplate.execute .

restTemplate.execute(uri,HttpMethod.GET,requestCallBack,clientHttpResponse -> {
                File ret = File.createTempFile("download", ".zip",new File("/Users/bokkavijay/Desktop"));
                StreamUtils.copy(clientHttpResponse.getBody(), new FileOutputStream(ret));
                return ret;
            });

above snippet can copy the file to our local with out time out but this is not what I need.

how can we pipe the stream in clientHttpResponse to controller ?

Answer 1

I found the working implementation

Controller

    @GetMapping("/readResponseAsStream")
        public ResponseEntity<StreamingResponseBody> downloadAsStream(Model model,HttpServletResponse response) {

             HttpHeaders httpHeaders=new HttpHeaders();
             httpHeaders.add("Transfer-Encoding","chunked");
             httpHeaders.add("Content-Type","x-zip-compressed");
             httpHeaders.add("Content-Disposition", "attachment;filename=sample.zip");

            ServletOutputStream servletOutputStream=response.getOutputStream();

            StreamingResponseBody downloadFile = out -> {
                 

                      RequestCallback requestCallBack=request->{
                            request.getHeaders().add(//Add headers here);
                      };

                      ResponseExtractor<ServletOutputStream> responseExtractor = clientHttpResponse -> {

                              //code snippet if you want to write response stream to HttpServletResponse
                              byte[] buff = new byte[800000];
                              int bytesRead = 0;
                                  while ((bytesRead = clientHttpResponse.getBody().read(buff)) != -1) {
                                    servletOutputStream.write(buff, 0, bytesRead);
                                    }
                              return servletOutputStream;


                              //Incase if you want to copy file to you local
                               File ret = File.createTempFile("download", ".zip",new File("Add Local system directory address here"));
                               StreamUtils.copy(clientHttpResponse.getBody(), new FileOutputStream(ret));

                               //You can copy the the clientHttpResponse.getBody() to ByteArrayInputStream and return
                               // Don't return clientHttpResponse.getBody() directly because rest template will close the inputStream(clientHttpResponse.getBody()) after .execute completed

                               //if you want to write restTemplate.execute in dao layer , pass servletOutputStream as a argument to method

                              };

                   restTemplate.execute(URL_ADDRESS,HttpMethod.GET,requestCallBack,responseExtractor);


            };


            return new ResponseEntity(downloadFile,httpHeaders,HttpStatus.OK);
}

If you write the response directly to HttpServletResponse , controller download the file when we access in browser