Spring Boot REST API: Handling Conditional GET Requests with ETag for Resource Optimization
I'm following best practices but I'm trying to debug Hey everyone, I'm running into an issue that's driving me crazy... I'm currently implementing a REST API using Spring Boot (version 2.5.4) and I'm facing challenges with optimizing resource retrieval using ETags for conditional GET requests. My goal is to improve performance by ensuring that clients only receive data when it has changed since their last request. I've set up my controller method as follows: ```java @GetMapping("/api/resource/{id}") public ResponseEntity<MyResource> getResource(@PathVariable String id, @RequestHeader(HttpHeaders.IF_NONE_MATCH) String ifNoneMatch) { MyResource resource = resourceService.findById(id); String eTag = generateETag(resource); if (eTag.equals(ifNoneMatch)) { return ResponseEntity.status(HttpStatus.NOT_MODIFIED).eTag(eTag).build(); } return ResponseEntity.ok() .eTag(eTag) .body(resource); } ``` However, I'm receiving a 304 Not Modified response when the resource has indeed changed, which is unexpected. The `generateETag` method looks like this: ```java private String generateETag(MyResource resource) { return Integer.toHexString(resource.hashCode()); } ``` I've verified that the resource does change (the database entry is updated), but the client always gets a 304 response after the first request. I suspect that the issue might be related to how I'm generating the ETag or how I'm handling the request headers. Additionally, I'm setting the `ETag` in the `ResponseEntity` but I'm unsure if it’s being sent correctly. I've tried logging the values of `eTag` and `ifNoneMatch`, and they seem to match after the initial request, even when the resource has changed. Could anyone provide insight into how to properly implement ETags in this scenario? What best practices should I follow when working with conditional requests in Spring Boot? Has anyone else encountered this? For reference, this is a production mobile app. This is part of a larger CLI tool I'm building. I've been using Java for about a year now. Any pointers in the right direction?