Minimize the impact on memory on generating and downloading a file - spring-boot

Question

For testing purposes only, I created this controller, which generates a 100MB file and returns it to the client. The method is very fast. The content of the file does not matter. The file is generated on the fly, it is not saved to disk.
Is it possible to reduce the impact on memory, particularly on java heap? Thank you
#GetMapping("/testDownload100MB")
public ResponseEntity<Resource> download100MB() throws IOException {
int sizeInBytes = 100 * 1024 * 1024;
ByteArrayOutputStream outStream = new ByteArrayOutputStream(sizeInBytes);
for (int i = 0; i < sizeInBytes; i++) {
outStream.write(0);
}
Resource resource = new ByteArrayResource(outStream.toByteArray());
return ResponseEntity.ok()
.headers(utilities.getGenericHttpHeadersToDownloadFile())
.contentLength(sizeInBytes)
.contentType(MediaType.APPLICATION_OCTET_STREAM)
.body(resource);
}
The code of utilities.getGenericHttpHeadersToDownloadFile() is not relevant for the question, however I report it for completeness:
public HttpHeaders getGenericHttpHeadersToDownloadFile() {
HttpHeaders headers = new HttpHeaders();
headers.add(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=myfile");
headers.add("Cache-Control", "no-cache, no-store, must-revalidate");
headers.add("Pragma", "no-cache");
headers.add("Expires", "0");
return headers;
}

Answer 1

Solved.
The code in my question throws a java.lang.OutOfMemoryError: Java heap space on my Spring Boot server. This new code solves the issue:
#GetMapping("/testDownload100MB")
public ResponseEntity<Resource> download100MB() throws IOException {
int size1MB = 1 * 1024 * 1024; // size in bytes
File tempFile = new File(System.getProperty("user.home") + File.separator + "tempFile" + System.currentTimeMillis());
for (int i = 0; i < 100; i++) {
ByteArrayOutputStream outStream = new ByteArrayOutputStream(size1MB);
for (int j = 0; j < size1MB; j++) {
outStream.write(0);
}
FileUtils.writeByteArrayToFile(tempFile, outStream.toByteArray(), true); // append to the temp file
}
Resource resource = new FileSystemResource(tempFile);
Timer timer = new Timer();
timer.schedule(new TimerTask() {
#Override
public void run() {
// we can assume that the file can be safely deleted after five minutes
tempFile.delete();
}
}, 1000 * 60 * 5);
return ResponseEntity.ok()
.headers(utilities.getGenericHttpHeadersToDownloadFile())
.contentLength(tempFile.length())
.contentType(MediaType.APPLICATION_OCTET_STREAM)
.body(resource);
}
Note that FileUtils must be imported with: import org.apache.commons.io.FileUtils;.
In this case, no objects exceeding 1 MB are placed in the java heap. In addition, FileSystemResource does not need to load the entire file into memory. On the other hand, I had to add a timer to delete the file: since this is a method for testing purposes, I can safely assume that after a few minutes the file is no longer needed.
If there are better solutions that do not require a temporary file, add your answer :)