Http Headers

In this first example we are going to build a simple Veronica application to show how to work with Http headers

Here's a list of the required preliminary knowledge for this tutorial:

• Basic application initialization
• How to create a route
• How to initialize the application router

If you lack the preliminary knowledge, we advise you to go back to previous tutorials to get started. Here's a list of the topics that we are going to cover in this tutorial:

• Http headers manipulation

We are going to create an application that reads the Accept Http header of the request, and returns three different responses depending on its content. Let's get started:

1. First we need to define a simple route for our application

Java

Route<Request, Response> route = Route.builder()
  .requestHandler(req -> {
    // TODO
    return ok(Response.builder().build());
  })
  .build();

2. We now need to implement our RequestHandler:

Java

Route<Request, Response> route = Route.builder()
    .requestHandler(req -> {

        Response response;

        switch (req.getHeaders().getFirst("accept").toLowerCase()) {

            case "application/json":
                response = Response.builder()
                    .body("{\"message\": \"Hello, world!\"}")
                    .build();

                break;

            case "text/html":
                response = Response.builder()
                    .body("<h1>Hello, world!</h1>")
                    .build();

                break;

            default:
                response = Response.builder()
                    .body("Hello, world!")
                    .build();

        }

        return ok(response);
    })
    .build();

3. For completeness, we might also want to specify the Content-Type response header:

Java

Route<Request, Response> route = Route.builder()
    .requestHandler(req -> {

        Response response;

        switch (req.getHeaders().getFirst("accept").toLowerCase()) {

            case "application/json":
                response = Response.builder()
                    .body("{\"message\": \"Hello, world!\"}")
                    .header("Content-Type", "application/json")
                    .build();

                break;

            case "text/html":
                response = Response.builder()
                    .body("<h1>Hello, world!</h1>")
                    .header("Content-Type", "text/html")
                    .build();

                break;

            default:
                response = Response.builder()
                    .body("Hello, world!")
                    .header("Content-Type", "text/plain")
                    .build();

        }

        return ok(response);
    })
    .build();

4. And now we build our application

Java

Route<Request, Response> route = Route.builder()
    .requestHandler(req -> {

        Response response;

        switch (req.getHeaders().getFirst("accept").toLowerCase()) {

            case "application/json":
                response = Response.builder()
                    .body("{\"message\": \"Hello, world!\"}")
                    .header("Content-Type", "application/json")
                    .build();

                break;

            case "text/html":
                response = Response.builder()
                    .body("<h1>Hello, world!</h1>")
                    .header("Content-Type", "text/html")
                    .build();

                break;

            default:
                response = Response.builder()
                    .body("Hello, world!")
                    .header("Content-Type", "text/plain")
                    .build();

        }

        return ok(response);
    })
    .build();

    Router<Request, Response> router = Router.builder()
        .fallbackRoute(route)
        .build();

int port = 8000;

Application<Request, Response> app = Application.basic()
    .port(port)
    .router(router)
    .build();

app.start();