Handling Conditional GET Requests with ETags in a Spring Boot REST API
I've been working on this all day and I'm implementing a REST API in Spring Boot (version 2.6.3) and trying to optimize the performance of my GET requests using ETags... I want to return a 304 Not Modified status when the resource has not changed since the last request. However, I’m facing an issue where the ETag I’m generating does not seem to be recognized by the client, leading to unnecessary data transfer. In my controller, I have the following code that generates an ETag based on the resource's last modified time: ```java @GetMapping("/resource/{id}") public ResponseEntity<Resource> getResource(@PathVariable Long id) { Resource resource = resourceService.findById(id); String eTag = String.valueOf(resource.getLastModified().getTime()); if (request.getHeader("If-None-Match") != null && request.getHeader("If-None-Match").equals(eTag)) { return ResponseEntity.status(HttpStatus.NOT_MODIFIED).build(); } return ResponseEntity.ok() .eTag(eTag) .body(resource); } ``` I have also ensured that the client is sending the correct `If-None-Match` header, but I keep receiving a 200 OK status even when the resource has not changed. I tried logging the ETag values and the `If-None-Match` header values, and they seem to match. I also tested the API using Postman and confirmed that the header is being sent correctly. Additionally, I’ve verified that there are no filters or interceptors altering the response. Is there something I might be missing in the configuration, or is there a best practice around generating and validating ETags in Spring Boot that I should follow? Any insights would be greatly appreciated! Any help would be greatly appreciated!