Guice call init method after instantinating an object

Question

Is it possible to tell Guice to call some method (i.e. init()) after instantinating an object of given type?

I look for functionality similar to @PostConstruct annotation in EJB 3 (and Spring).

Answer 1

You can just add the @Inject annotation to your init() method. It will get run automatically after the object is instantiated.

Answer 2

Actually, it is possible.

You need to define a TypeListener to get the functionality going. Something along the lines of the following in your module definition:

bindListener(Matchers.subclassesOf(MyInitClass.class), new TypeListener() {
    @Override
    public <I> void hear(final TypeLiteral<I> typeLiteral, TypeEncounter<I> typeEncounter) {
        typeEncounter.register(new InjectionListener<I>() {
            @Override
            public void afterInjection(Object i) {
                MyInitClass m = (MyInitClass) i;
                m.init();
            }
        });
    }
});

Answer 3

guiceyfruit does what you're after for methods annotated with @PostConstruct or implementing spring's InitializingBean. It's also possible to write your own listeners to do this. Here's an example that calls a public init() method after objects are created.

import com.google.inject.*;
import com.google.inject.matcher.*;
import com.google.inject.spi.*;

public class MyModule extends AbstractModule {
  static class HasInitMethod extends AbstractMatcher<TypeLiteral<?>> {
    public boolean matches(TypeLiteral<?> tpe) {
      try {
        return tpe.getRawType().getMethod("init") != null;
      } catch (Exception e) {
        return false;
      }
    }

    public static final HasInitMethod INSTANCE = new HasInitMethod();
  }

  static class InitInvoker implements InjectionListener {
    public void afterInjection(Object injectee) {
      try {
        injectee.getClass().getMethod("init").invoke(injectee);
      } catch (Exception e) {
        /* do something to handle errors here */
      }
    }
    public static final InitInvoker INSTANCE = new InitInvoker();
  }

  public void configure() {
    bindListener(HasInitMethod.INSTANCE, new TypeListener() {
      public <I> void hear(TypeLiteral<I> type, TypeEncounter<I> encounter) {
        encounter.register(InitInvoker.INSTANCE);
      }
    });
  }
}