# etag-caching

Companion module for [**Mastering Cache Control with ETag in Spring Boot RESTful APIs**](https://ankurm.com/etag-cache-control-rest-api-spring-boot/)
on ankurm.com, re-verified against Spring Boot 4.1.1 / Spring Framework 7.0.9.

`mvn test` regenerates every transcript in [`docs/output/`](docs/output).

## Versions

| | |
|---|---|
| Spring Boot | 4.1.1 |
| Spring Framework | 7.0.9 |
| JDK | Eclipse Temurin 25.0.4.1 (LTS) |

## Quickstart

```bash
export JAVA_HOME=/path/to/jdk-25
mvn -DskipTests package
./scripts/run.sh
curl -i http://localhost:8080/api/products/42
mvn test               # 5 tests, regenerates docs/output/
```

## Endpoints

| Endpoint | Shows |
|---|---|
| `GET /api/products/{id}` | deep cache: `WebRequest.checkNotModified()` before the "expensive" part |
| `PUT /api/products/{id}` | conditional update with `If-Match`, optimistic locking, ETag rotation |
| `GET /api/echo/{message}` | shallow cache: zero-code `ShallowEtagHeaderFilter` on a scoped URL pattern |

## Documentation

1. [spring-boot-starter-web is deprecated in favour of spring-boot-starter-webmvc](docs/01-starter-web-renamed.md)
2. [ETags are unchanged, verified rather than assumed](docs/02-etags-unchanged-verified.md)
3. [Deep cache vs shallow cache, and conditional PUT with If-Match](docs/03-deep-vs-shallow-cache.md)

## Findings worth the trip

- **`spring-boot-starter-web`'s own published POM now says "deprecated in favor of
  spring-boot-starter-webmvc"** -- read directly off Maven Central, not a migration guide. Both
  resolve to an identical dependency set today.
- **`ShallowEtagHeaderFilter`, `WebRequest.checkNotModified()`, and `ResponseEntity.eTag()` are
  all unchanged** on Spring Framework 7.0.9 -- same packages, same behaviour, confirmed by
  compiling and running against them rather than assumed from the Boot 3 version of this article.
- **Registering `ShallowEtagHeaderFilter` as a plain `@Bean` applies it globally**; this module
  scopes it to one URL pattern with `FilterRegistrationBean` instead, so it does not shadow the
  deliberately deeper caching on `/api/products`.

## License

MIT -- see [LICENSE](../LICENSE).