Flash5/flash-extensions/flash-ext-openapi/README.md

flash-ext-openapi

OpenAPI 3.0.3 generation + Swagger UI for Flash.

What it provides

Route	Description
GET /openapi.json	OpenAPI spec JSON
GET /openapi.yaml	OpenAPI spec YAML
GET /openapi/swagger	Swagger UI

Install

FlashApp.create(8080)
    .install(new JacksonExtension())
    .install(new OpenApiExtension("/openapi", "My API", "1.0.0"))
    .scan("com.acme.handlers")
    .startAndBlock();

Operation annotation

@GET("/users/{id}")
@ApiOperation(summary = "Get user", description = "Returns one user", tags = {"users"})
@Parameter(name = "expand", in = ParameterIn.QUERY, type = SchemaType.STRING, examples = {"roles", "permissions"})
@APIResponse(
    responseCode = "200",
    description = "User found",
    content = @Content(contentType = ContentType.JSON, schema = UserDto.class)
)
public final class GetUser extends RequestHandler { ... }

Response patterns

Single object

@APIResponse(
    responseCode = "200",
    description = "User found",
    content = @Content(contentType = ContentType.JSON, schema = UserDto.class)
)

Array

@APIResponse(
    responseCode = "200",
    description = "Users listed",
    content = @Content(contentType = ContentType.JSON, schema = UserDto.class, array = true)
)

No content

@APIResponse(
    responseCode = "204",
    description = "Deleted",
    content = @Content(contentType = ContentType.NONE)
)

Inferred from handler return type

@APIResponse(
    responseCode = "200",
    content = @Content
)

If content.schema is omitted, schema is inferred from the handler handle(...) return type. Explicit content.schema always wins over inference.

Inference defaults:

• UserDto -> object schema for UserDto
• List<UserDto> / Set<UserDto> / UserDto[] -> array with items: UserDto
• Map<String, UserDto> -> object with additionalProperties: UserDto

DTO schema metadata

@Schema(name = "User", title = "User DTO", description = "Public user", deprecated = false)
public class UserDto {

    @SchemaProperty(title = "ID", required = true, example = "USR-100", enumeration = {"USR-100", "USR-101"})
    public String id;

    @SchemaProperty(hidden = true)
    public String internalDebug;
}

Supported field-level exclusion:

• @Schema(hidden = true) / @SchemaProperty(hidden = true)
• @JsonIgnore
• @JsonIgnoreProperties(...)
• transient / static

Contributor API

OpenAPI is extension-agnostic. Other extensions contribute with OpenApiContributor via OpenApiContributorRegistry.

Supported contribution surfaces:

• components fragments (merged with last-wins)
• operation security requirements (additive)
• operation responses and response headers (additive)

Merge policy:

• contributor collisions use last-wins
• manual @APIResponse description always wins over contributors for the same status

OIDC interop

When flash-ext-oidc is installed, OpenAPI integrates automatically:

• security scheme under components.securitySchemes
• per-operation security
• auto responses (class-based handlers):
  • 401 Authentication required
  • 403 role/scope required messages when applicable

Manual @APIResponse for the same status code always wins.

Limiter interop

When flash-ext-limiter is installed, handlers with @Limit automatically get response headers documented in OpenAPI:

• X-RateLimit-Limit
• X-RateLimit-Remaining
• X-RateLimit-Reset
• Retry-After on 429

If 429 is missing, it is auto-added as Too Many Requests.

Notes

• Operations are collected from final boot-time routes for class-based handlers with @ApiOperation.
• Documented paths always match runtime paths (including scope namespaces/prefixes/rewrites).
• Route path params are auto-discovered from /{id}.
• Parameter annotations are mainly for query/header/cookie enrichment.
• Output responses are sorted by numeric status code.