api-versioning

# API Versioning (Boot 4 / Framework 7)

Spring Framework 7 provides API versioning in the mapping layer. Prefer it over hand-rolled
`/v1` prefixes, custom `HandlerMapping` implementations, or version-sniffing filters.

## Declare versions on mappings

```java
@RestController
@RequestMapping("/api/orders")
class OrderController {

    @GetMapping(path = "/{id}", version = "1.0")
    OrderV1 getV1(@PathVariable UUID id) { ... }

    @GetMapping(path = "/{id}", version = "1.2")
    OrderV2 getV2(@PathVariable UUID id) { ... }
}
```

Use semantic version strings. A `+` suffix means the mapping handles that version and newer
versions, for example `version = "1.2+"`.

## Configure one request resolution strategy

```java
@Configuration
class WebConfig implements WebMvcConfigurer {
    @Override
    public void configureApiVersioning(ApiVersionConfigurer configurer) {
        configurer
            .useRequestHeader("API-Version")
            .setDefaultVersion("1.0")
            .addSupportedVersions("1.0", "1.2");
    }
}
```

Choose exactly one source: request header, query parameter, path segment, or media-type
parameter. Keep the choice consistent across the application. WebFlux uses the corresponding
`WebFluxConfigurer` hook.

## Required behavior and deprecation

Versioning is required unless a default is configured or `setVersionRequired(false)` is used.
Missing or unsupported versions should be covered by the API error contract. Use
`StandardApiVersionDeprecationHandler` for `Deprecation`, `Sunset`, and `Link` response headers.

Boot properties can provide defaults under `spring.mvc.apiversion.*` or
`spring.webflux.apiversion.*`, but keep the resolution strategy in Java configuration when its
behavior must be explicit.

## Gotchas

- Agent hand-rolls `/api/v1` prefixes or a version filter - use the mapping `version` attribute.
- Agent writes `version = 1` - the value is a semantic version `String`, such as `"1.0"`.
- Agent uses `useHeader` or `useQueryParameter` - use `useRequestHeader` or `useQueryParam`.
- Agent enables versioning without a default or `versionRequired(false)` - un-versioned requests return 400.
- Agent mixes a path segment and a request header - choose one source of truth.
- Agent invents custom sunset headers - use `StandardApiVersionDeprecationHandler`.