java 35 lines · 6 steps

HTTP caching with ETags in Spring

A shallow ETag filter plus Cache-Control headers cut bandwidth by letting clients revalidate and reuse product responses.

Explained by highlit
Spring Intermediate http-caching etag servlet-filters rest conditional-requests
1@Configuration
2public class WebConfig {
3 
4 @Bean
5 public FilterRegistrationBean<ShallowEtagHeaderFilter> shallowEtagHeaderFilter() {
6 FilterRegistrationBean<ShallowEtagHeaderFilter> registration =
7 new FilterRegistrationBean<>(new ShallowEtagHeaderFilter());
8 registration.addUrlPatterns("/api/products/*");
9 registration.setName("etagFilter");
10 registration.setOrder(Ordered.HIGHEST_PRECEDENCE + 10);
11 return registration;
12 }
13}
14 
15@RestController
16@RequestMapping("/api/products")
17class ProductController {
18 
19 private final ProductRepository productRepository;
20 
21 ProductController(ProductRepository productRepository) {
22 this.productRepository = productRepository;
23 }
24 
25 @GetMapping("/{id}")
26 public ResponseEntity<ProductView> getProduct(@PathVariable Long id) {
27 Product product = productRepository.findById(id)
28 .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND));
29 
30 ProductView body = ProductView.from(product);
31 return ResponseEntity.ok()
32 .cacheControl(CacheControl.maxAge(Duration.ofMinutes(5)).cachePublic())
33 .body(body);
34 }
35}
01 / 01
STEP 01

Walkthrough

Space play ←→ step click any line
Three takeaways
  1. 1A shallow ETag filter hashes the rendered response body so unchanged content returns 304 without re-sending it.
  2. 2Scoping a FilterRegistrationBean to a URL pattern keeps expensive filters off routes that don't need them.
  3. 3Cache-Control and ETag work together: one sets freshness lifetime, the other enables cheap revalidation after it expires.

Related explainers

java 
@Component
@Converter
public class EncryptedStringConverter implements AttributeConverter<String, String> {
 

Transparent column encryption in Spring & JPA

encryption aes-gcm jpa-converter
Advanced 10 steps
go 
package api
 
import (
	"crypto/sha256"

ETag conditional requests in Gin

http-caching etag conditional-requests
Intermediate 6 steps
java 
package com.acme.billing.config;
 
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.ConfigurationProperties;

Feature-flagged beans with Spring @ConditionalOnProperty

feature-flags conditional-beans strategy-pattern
Intermediate 5 steps
java 
public static Map<String, String> parseCookieHeader(String header) {
    Map<String, String> cookies = new LinkedHashMap<>();
    if (header == null || header.isBlank()) {
        return cookies;

Parsing an HTTP Cookie header in Java

string-parsing http url-decoding
Intermediate 6 steps
java 
public class TimedSocketReader {
 
    private static final int READ_TIMEOUT_MS = 5_000;
    private static final int CONNECT_TIMEOUT_MS = 3_000;

Reading a socket with connect and read timeouts

sockets timeouts io
Intermediate 8 steps
java 
public final class EncodingDetector {
 
    public enum Encoding {
        UTF_8, UTF_16LE, UTF_16BE, UTF_32LE, UTF_32BE, ASCII, UNKNOWN

Detecting text encoding from raw bytes in Java

byte-manipulation encoding-detection bitwise-operations
Intermediate 8 steps

Share this explainer

Here's the card — post it anywhere.

HTTP caching with ETags in Spring — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code