Launcher

Features

Launcher is essentially a highly abstracted and generalized implementation of main() methods, combined with Service Graph, and support of start/stop semantics
Takes care of full application lifecycle and logging
Perfectly compatible with ActiveJ Inject

Launcher is a very explicit tool. You can understand how it works by simply looking at the implementation of its main method launch in a nutshell:

public void launch(String[] args) throws Exception {
    logger.info("=== INJECTING DEPENDENCIES");
    Injector injector = createInjector(args);
    logger.info("Eager instances: " + injector.createEagerInstances());
    Set<LauncherService> services = injector.getInstance(new Key<Set<LauncherService>>() {});
    Set<LauncherService> startedServices = new HashSet<>();
    logger.info("Post-inject instances: " + injector.postInjectInstances());
  		
    logger.info("=== STARTING APPLICATION");
    logger.info("Starting LauncherServices: " + services);
    startServices(services, startedServices);
    onStart();
    onStartFuture.complete(null);
  
    logger.info("=== RUNNING APPLICATION");
    run();
    onRunFuture.complete(null);
  
    logger.info("=== STOPPING APPLICATION");
    onStop();
    stopServices(startedServices);
    onCompleteFuture.complete(null);
}

Step-by-step examination:

Create the Injector with the Modules provided in Launcher
Inject top-level dependencies into the Launcher instance itself
Instantiate all keys marked as @Eager multibinder keygroup, exported by Launcher’s Modules
Start all services from Set<LauncherService> multibinder set, exported by Launcher’s Modules, and execute onStart() method
Execute run() method
After run() is finished (either due to finishing all app-specific computations or by responding to a shutdown request such as SIGKILL), execute onStop() method and stop all services

Here is an example of Launcher lifecycle represented as logs (particularly, HttpServerLauncher subclass that provides an AsyncHttpServer, an Eventloop and Config). Launch this example:

public final class HttpHelloWorldExample extends HttpServerLauncher {
	@Provides
	AsyncServlet servlet() {
		return request -> HttpResponse.ok200().withPlainText("Hello World");
	}

	public static void main(String[] args) throws Exception {
		Launcher launcher = new HttpHelloWorldExample();
		launcher.launch(args);
	}
}

to see alike logs:

 === INJECTING DEPENDENCIES
Created eager singletons
Post-injected instances: [HttpHelloWorldExample]

=== STARTING APPLICATION
Starting LauncherServices: [io.active.net.jmx.JmxModule, io.active.net.service.ServiceGraphModule]
Starting LauncherService: io.active.net.jmx.JmxModule
Starting LauncherService: io.active.net.service.ServiceGraphModule
Creating ServiceGraph...
Starting services
Listening on [/0.0.0.0:8080]: AsyncHttpServer{listenAddresses=[/0.0.0.0:8080]}
Started io.active.net.http.AsyncHttpServer

=== RUNNING APPLICATION
HTTP Server is listening on http://localhost:8080/
 
=== STOPPING APPLICATION
Stopping LauncherService: io.active.net.jmx.JmxModule
Stopping LauncherService: io.active.net.service.ServiceGraphModule
Stopping ServiceGraph...
Stopping services

Launcher optionally requires the following dependencies from its Modules:
- @Eager multibinder keygroup
- Set<LauncherService> multibinder set

Launcher exports the following dependencies to its Modules:

class Launcher{
 	@NotNull
	public final Injector createInjector() {
	   return Injector.of(getInternalModule()
	                  .combineWith(getModule())
	                  .overrideWith(getOverrideModule()));
	}
  
  private Module getInternalModule() {
     Class<Launcher> launcherClass = (Class<Launcher>) getClass();
     Key<CompletionStage<Void>> completionStageKey = new Key<CompletionStage<Void>>() {};

     return Module.create()
         .bind(String[].class).annotatedWith(Args.class).toInstance(args)
         .bind(Launcher.class).to(launcherClass)
         .bind(launcherClass).toInstance(this)

         .postInjectInto(launcherClass)
         .bind(completionStageKey.named(OnStart.class)).toInstance(onStartFuture)
         .bind(completionStageKey.named(OnRun.class)).toInstance(onRunFuture)
         .bind(completionStageKey.named(OnComplete.class)).toInstance(onCompleteFuture)

         .scan(Launcher.this);
	}
  
  // this method can be overridden by subclasses which extend Launcher,
  // provides business logic modules (for example, ConfigModule)
  protected Module getModule() {
      return Module.empty();
  }
  
  // this method can be overridden by subclasses which extend Launcher,
  // overrides definitions in internal module
  protected Module getOverrideModule() {
      return Module.empty();
  }
}

@Args String[] arguments of its Launcher.launch(String[] args) method, corresponding to main(String[] args) method
The Launcher instance itself
@OnStart CompletionStage<Void> future which is completed when application is wired and started
@OnRun CompletionStage<Void> future which is completed when Launcher.run() is complete.
@OnComplete CompletionStage<Void> future which is completed when application is stopped

Launcher also has handy diagnostic and JMX properties:

Instant of launch, start, run, stop, and complete
Duration of start, run, stop, and total duration
Throwable applicationError property

More examples

Note: To run the examples, you need to clone ActiveJ from GitHub:
$ git clone https://github.com/activej/activej
And import it as a Maven project. Check out tag v4.1. Before running the examples, build the project.
The two following examples are located at activej -> examples -> core -> boot and activej -> examples -> core -> http respectively

Hello World Example

Here is a simple “Hello World” Launcher application using ActiveJ Inject:

public final class HelloWorldExample extends Launcher {
	@Inject
	String message;

	@Provides
	String message() {
		return "Hello, world!";
	}

	@Override
	protected void run() {
		System.out.println(message);
	}

	public static void main(String[] args) throws Exception {
		Launcher launcher = new HelloWorldExample();
		launcher.launch(args);
	}
}

See full example on GitHub

HTTP Server from scratch using Launcher

When creating HTTP servers or any other applications, you can either use some predefined solutions (see examples) or simple Launcher instead. In this case, you’ll need to take care of all of the needed dependencies and override some basic methods:

public final class CustomHttpServerExample extends Launcher {
	private static final int PORT = 8080;

	@Provides
	Eventloop eventloop() {
		return Eventloop.create();
	}

	@Provides
	AsyncServlet servlet() {
		return request -> HttpResponse.ok200()
				.withPlainText("Hello from HTTP server");
	}

	@Provides
	@Eager
	AsyncHttpServer server(Eventloop eventloop, AsyncServlet servlet) {
		return AsyncHttpServer.create(eventloop, servlet).withListenPort(PORT);
	}

	@Override
	protected Module getModule() {
		return ServiceGraphModule.create();
	}

	@Override
	protected void run() throws Exception {
		logger.info("HTTP Server is now available at http://localhost:" + PORT);
		awaitShutdown();
	}

	public static void main(String[] args) throws Exception {
		Launcher launcher = new CustomHttpServerExample();
		launcher.launch(args);
	}
}

See full example on GitHub

Working with program arguments

To access program arguments from within Launcher you need to pass those arguments to Launcher#launch method. Then there are two ways for accessing arguments:

Using Launcher’s String[] args field
Requesting arguments using Dependency Injection. A key is String[].class annotated with @Args annotation. The following example illustrates both cases:

public final class LauncherArgsExample extends Launcher {

	@Inject
	Injector injector;

	@Override
	protected void run() {
		System.out.println("Received args: " + Arrays.toString(args));

		String[] injectedArgs = injector.getInstance(Key.of(String[].class, Args.class));
		System.out.println("Args retrieved from DI: " + Arrays.toString(injectedArgs));
	}

	public static void main(String[] args) throws Exception {
		new LauncherArgsExample().launch(args);
	}
}

See full example on GitHub

Async I/O

Boot

Misc

Launcher

Features

More examples

Hello World Example

HTTP Server from scratch using Launcher

Working with program arguments