Beginner LevelREST APIs & Web Services
How do Cache-Control headers, ETag, and If-None-Match enable HTTP response caching?
❓ Interview Prompt: Explain HTTP caching headers: `Cache-Control` (`max-age`, `no-cache`, `no-store`), `ETag` validation hashes, and `304 Not Modified` responses.
HTTP Caching reduces network latency and backend database load:
Directives & Headers:
1
'Cache-Control': Directs browser/CDN caching policies ('max-age=3600', 'no-cache' forces validation, 'no-store' forbids caching sensitive data).
2
'ETag' (Entity Tag): Server generates a unique hash representing the response body content.
3
Conditional Requests: Client sends 'If-None-Match: "hash_123"'. If response content hasn't changed, server returns '304 Not Modified' with an empty body, saving bandwidth!
Code Implementation Example
http
// Initial Response:
HTTP/1.1 200 OK
Cache-Control: public, max-age=86400
ETag: "w/686897696a5c1"
// Subsequent Conditional Client Request:
GET /api/v1/catalog HTTP/1.1
If-None-Match: "w/686897696a5c1"
// Server Response:
HTTP/1.1 304 Not Modified💡HTTP ETag validation returning 304 Not Modified to save bandwidth.
🎯 Interview Key Takeaway
Use ETags and Cache-Control headers to validate cached resources and return 304 Not Modified when data is unchanged.
#Caching#ETag#Cache-Control#Beginner
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