Provider extending

Question

I need to create provider for session scopes, like ServletScopes.SESSION, but with one extra action after object construction (like add listener). First idea - to extend ServletScopes.SESSION and override some method, but, unfortunately ServletScopes.SESSION is object, not class. So, how I can get such provider without copy-pasting code from ServletScopes?

Answer 1

First create an annotation:

import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

@Target({TYPE, METHOD})
@Retention(RUNTIME)
public @interface AfterInjectionListener
{
}

Then, annotate every class that implements a method `afterInjection()' with the annotation and add this binding to one of your Guice modules:

bindListener(Matchers.any(), new TypeListener()
{
  @Override
  public <I> void hear(TypeLiteral<I> typeLiteral, TypeEncounter<I> iTypeEncounter)
  {
    if (typeLiteral.getRawType().isAnnotationPresent(AfterInjectionListener.class))
    {
      logger.debug("adding injection listener {}", typeLiteral);
      iTypeEncounter.register(new InjectionListener<I>()
      {
        @Override
        public void afterInjection(I i)
        {
          try
          {
            logger.debug("after injection {}", i);
            i.getClass().getMethod("afterInjection").invoke(i);
          } catch (NoSuchMethodException e)
          {
            logger.trace("no such method", e);
          } catch (Exception e)
          {
            logger.debug("error after guice injection", e);
          }
        }
      });
    }
  }
});

Place a breakpoint inside of afterInjection() method, run the app in debugging mode and check if the method is called after injection.