api-versioning

# API Versioning (Boot 3 / Framework 6) Boot 3 does not provide Boot 4's built-in mapping `version` attribute. Choose one explicit strategy and keep it consistent: URL segments, a request header, or media-type parameters. ## Prefer a visible, testable contract For a public API, `/api/v1/orders` and `/api/v2/orders` are usually the clearest choice. If URLs must remain stable, resolve a request header at the web boundary and route to versioned handlers. Do not hide version selection in business services or duplicate it across filters and controllers. ```java @RestController @RequestMapping("/api/v1/orders") class OrderV1Controller { @GetMapping("/{id}") OrderV1 get(@PathVariable UUID id) { ... } } ``` Document supported versions in OpenAPI, define a removal policy, and return a consistent error for unsupported versions. Add `Deprecation`, `Sunset`, and `Link` headers through a response advice or filter when retiring a version. ## Migration boundary Keep version-specific DTOs and controllers thin. Map both versions to the same application use case, and do not copy domain logic into each version. Add contract tests for every supported version and verify content negotiation if using media types. ## Gotchas - Agent uses Boot 4's `version` attribute on Boot 3 - it is not available; choose an explicit routing strategy. - Agent mixes URL, header, and media-type resolution - select one source of truth. - Agent puts version branching in services - keep compatibility at ...