Commons Inject – Application Lifecycle Support

Commons Inject provides limited application lifecycle support. More specifically, you can have your Pojo's initialized when the application starts and you can also have them perform a graceful shutdown hen the application terminates.

To achieve that, you must use the @PostConstruct, and @PreDestroy annotations, like this:

public class MyBean
  @Inject private ConnectionProvider connectionProvider;

  @PostConstruct
  public void init() throws SomeException {
    // Perform initialization on this bean.
  }

  @PreDestroy
  public void shutdown() throws OtherException {
    // Release resources, etc...
  }
}

The specification of @PostConstruct, and @PreDestroy demands, that such methods must be public, non-static, non-abstract, and must not expect parameters. Of course, you need access to other beans, or the like, you can have them injected via @Inject. If there are multiple beans with @PostConstruct: For eager singletons, the order of invocation depends on the order of binding in the modules. Lazy singletons are initialized upon first use. (Injection into another bean counts as use.)

Beans with @PreDestroy, OTOH, are invoked in reverse order of initialization.

Two other things must be done to make use of @PostConstruct, and @PreDestroy:

The predefined PostConstructModule must be used when creating the injector. (This module must be the first in your module list.)

You must invoke the methods start() and shutdown() on the modules lifecycle controller

In other words, a typical application would look like this:

public class MyApp {
  public static void main() throws Exception {
    final IModule postConstructModule = new PostConstructModule();
    final IModule module1 = new MyModule1();
    final IModule module2 = new MyModule2();
    // Note: The PostConstructModule is first in the list.
    final IInjctor injector = CommonsInject.build(postConstructModule, module1, module2);
    // A binding for the controller was created automatically by the PostConstructModule.
    final ILifecycleController controller = injector.getInstance(ILifecycleController.class);
    // Initialize the beans with @PostConstruct
    controller.start();
    // Do the real work here.
    ...
    // Terminate the beans with @PreDestroy
    controller.shutdown();
  }
}

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