Enkan System

Enkan system is a container of components for managing the lifecycle and dependencies.
It’s inspired by clojure component.

Usage

Enkan system is composed of components.

EnkanSystem system = EnkanSystem.of(
    "http", new UndertowComponent()
);

Using of method, components are registered to Enkan system.

Creating components

Components must be extended SystemComponent class. And implements ComponentLifecycle.

class SomeComponent extends SystemComponent {
    @Override
    protected ComponentLifecycle<SomeComponent> lifecycle() {
        return new ComponentLifecycle<SomeComponent>() {
            @Override
            public void start(SomeComponent component) {
            }

            @Override
            public void stop(SomeComponent component) {
            }
        }
    }
}

ComponentLifecycle interface have 2 methods, start and stop. Their are called sequentially.
So all components are started and stopped safely.

Relationships between components

Components often depend on each other. For example, an application component needs a template engine and a database provider, and the database provider itself needs a datasource. You declare these relationships with relationships():

system.relationships(
    component("http").using("app"),
    component("app").using("template", "doma", "datasource"),
    component("doma").using("datasource"),
    component("flyway").using("datasource")
);

component("X").using("Y", "Z") means: X depends on Y and Z.

Enkan uses these declarations to do two things automatically:

1. Startup ordering — dependencies are started before the components that use them. In the example above, datasource starts first, then doma and flyway, then app, then http.
2. Dependency injection — each component’s fields annotated with @Inject are populated with the declared dependencies before start() is called.

If a declared dependency is not registered in the system, Enkan throws a MisconfigurationException at startup — not at request time.

core.COMPONENT_NOT_FOUND: Component 'datasource' not found (required by 'doma')

Inject components

Components are injected to a field of another component and middlewares.

For injecting to a field, put the Inject annotation on it.

@Inject
private TemplateEngine templateEngine;

If a class has multiple fields of same type, you can put the Named annotation for distinct.

@Named("freemarker")
@Inject
private TemplateEngine freemarker;

@Named("thymeleaf")
@Inject
private TemplateEngine thymeleaf;

Bootstrap the Enkan system

To start/stop the Enkan system, call the start() or stop() method.

system.start();

// ...

system.stop();

It is better to bootstrap a system in the REPL for the operation.

PseudoRepl repl = new PseudoRepl(MyExampleSystemFactory.class.getName());
ReplBoot.start(repl,
        new KotowariCommandRegister(),
        new DevelCommandRegister(),
        new MetricsCommandRegister());

PseudoRepl is a REPL server. The factory class for Enkan system.
ReplBoot is a tool for starting the REPL server and registering some commands to the REPL at same time.