High-level Server-Side API

In addition to the Low-Level Server-Side API Akka HTTP provides a very flexible “Routing DSL” for elegantly defining RESTful web services. It picks up where the low-level API leaves off and offers much of the higher-level functionality of typical web servers or frameworks, like deconstruction of URIs, content negotiation or static content serving.

To use the high-level API you need to add a dependency to the akka-http module.

Handling HTTP Server failures in the High-Level API

There are various situations when failure may occur while initialising or running an Akka HTTP server. Akka by default will log all these failures, however sometimes one may want to react to failures in addition to them just being logged, for example by shutting down the actor system, or notifying some external monitoring end-point explicitly.

Bind failures

For example the server might be unable to bind to the given port. For example when the port is already taken by another application, or if the port is privileged (i.e. only usable by root). In this case the “binding future” will fail immediately, and we can react to it by listening on the CompletionStage’s completion:

import akka.NotUsed; import akka.actor.ActorSystem; import akka.http.javadsl.ConnectHttp; import akka.http.javadsl.ServerBinding; import akka.http.javadsl.model.HttpRequest; import akka.http.javadsl.model.HttpResponse; import akka.http.javadsl.server.Route; import akka.http.javadsl.Http; import akka.stream.ActorMaterializer; import akka.stream.javadsl.Flow; import java.io.IOException; import java.util.concurrent.CompletionStage; public class HighLevelServerBindFailureExample { public static void main(String[] args) throws IOException { // boot up server using the route as defined below final ActorSystem system = ActorSystem.create(); final ActorMaterializer materializer = ActorMaterializer.create(system); // HttpApp.bindRoute expects a route being provided by HttpApp.createRoute final HighLevelServerExample app = new HighLevelServerExample(); final Route route = app.createRoute(); final Flow<HttpRequest, HttpResponse, NotUsed> handler = route.flow(system, materializer); final CompletionStage<ServerBinding> binding = Http.get(system).bindAndHandle(handler, ConnectHttp.toHost("", 8080), materializer); binding.exceptionally(failure -> { System.err.println("Something very bad happened! " + failure.getMessage()); system.terminate(); return null; }); system.terminate(); } }

For a more low-level overview of the kinds of failures that can happen and also more fine-grained control over them refer to the Handling HTTP Server failures in the Low-Level API documentation.

Failures and exceptions inside the Routing DSL

Exception handling within the Routing DSL is done by providing ExceptionHandler s which are documented in-depth in the Exception Handling section of the documentation. You can use them to transform exceptions into HttpResponse s with appropriate error codes and human-readable failure descriptions.

File uploads

For high level directives to handle uploads see the FileUploadDirectives.

Handling a simple file upload from for example a browser form with a file input can be done by accepting a Multipart.FormData entity, note that the body parts are Source rather than all available right away, and so is the individual body part payload so you will need to consume those streams both for the file and for the form fields.

Here is a simple example which just dumps the uploaded file into a temporary file on disk, collects some form fields and saves an entry to a fictive database:

TODO missing example 1

You can transform the uploaded files as they arrive rather than storing then in a temporary file as in the previous example. In this example we accept any number of .csv files, parse those into lines and split each line before we send it to an actor for further processing:

TODO missing example 2