Cleanup file streaming utilities (#559)

* Cleanup file streaming.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Added missing comments.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Fix typo.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Split utility class.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Dependency cleanup.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Add missing dependency,

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Remove repository api dependency from rest core.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Fix build and sonar issues.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Remove custom ConstraintViolationException

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* RequestMapping should be public.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Fix errors.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Removed dead code.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Not null

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Fix nullpointer.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

* Code cleanup.

Signed-off-by: kaizimmerm <kai.zimmermann@bosch-si.com>

hawkbit-mgmt-api/src/main/java/org/eclipse/hawkbit/mgmt/rest/api/MgmtDownloadRestApi.java

@@ -8,6 +8,8 @@
  */
 package org.eclipse.hawkbit.mgmt.rest.api;
 
+import java.io.InputStream;
+
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.PathVariable;
@@ -37,7 +39,7 @@ public interface MgmtDownloadRestApi {
      */
     @RequestMapping(method = RequestMethod.GET, value = MgmtRestConstants.DOWNLOAD_ID_V1_REQUEST_MAPPING)
     @ResponseBody
-    ResponseEntity<Void> downloadArtifactByDownloadId(@PathVariable("tenant") String tenant,
+    ResponseEntity<InputStream> downloadArtifactByDownloadId(@PathVariable("tenant") String tenant,
             @PathVariable("downloadId") String downloadId);
 
 }