flash-ext-jackson

Jackson JSON integration for the Flash HTTP server.

What it provides

Component	Description
`JacksonExtension`	Installs Jackson into the extension layer
`JacksonHandler`	Base class for handlers that need JSON I/O
Global exception handler	Maps `HttpException` → JSON error; all other exceptions → 500

Installation

<dependency>
    <groupId>dev.relism</groupId>
    <artifactId>flash-ext-jackson</artifactId>
    <version>1.0-SNAPSHOT</version>
</dependency>

FlashApp.create(8080)
    .install(new JacksonExtension())
    .install(new OpenApiExtension("/openapi", "My API", "1.0.0"))
    .start();

Install order is irrelevant — Flash's two-phase extension model ensures ObjectMapper is resolved before any extension that calls ctx.require(ObjectMapper.class) needs it.

Custom mapper

ObjectMapper mapper = JsonMapper.builder()
    .addModule(new JavaTimeModule())
    .disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
    .build();

FlashApp.create(8080)
    .install(new JacksonExtension(mapper));

JacksonHandler

Extend JacksonHandler to get bodyAs and json helpers without constructor boilerplate. The ObjectMapper is injected once at startup and shared across all subclasses.

@Route(method = HttpMethod.POST, path = "/api/blogs")
@ApiOperation(summary = "Create blog")
@ApiResponse(status = 201, description = "Created", schema = Blog.class)
@ApiResponse(status = 400, description = "Invalid body")
public class CreateBlog extends JacksonHandler {

    @Override
    public Object handle(Request req, Response res) throws Exception {
        CreateBlogRequest body = bodyAs(req, CreateBlogRequest.class);
        Blog created = service.create(body);
        res.status(201);
        return json(res, created);         // sets Content-Type: application/json
    }
}

Methods

Method	Description
`bodyAs(req, Type.class)`	Deserializes the request body; throws `HttpException` 400 on parse errors
`json(res, obj)`	Serializes `obj`, sets `Content-Type: application/json`, returns the JSON string
`jsonView(res, obj, View.class)`	Like `json` but applies a Jackson `@JsonView` filter

Exception handling

JacksonExtension installs a global exception handler that applies to every route:

HttpException(status, message)  →  HTTP <status>  {"error": "<message>"}
Any other Throwable             →  HTTP 500        {"error": "Internal Server Error"}

To throw a handled HTTP error from any handler:

throw HttpException.notFound("Blog not found");
throw HttpException.badRequest("Missing field: title");
throw HttpException.unauthorized();
throw HttpException.forbidden();

Lambda routes

For lambda-style routes, use the ObjectMapper directly from the context:

ObjectMapper mapper = app.ctx().require(ObjectMapper.class);

app.get("/api/status", (req, res) -> {
    res.type(ContentType.JSON);
    return mapper.writeValueAsString(Map.of("status", "ok"));
});

3.0 KiB Raw Blame History