Genie Custom Annotation Demo

Nicky Moelholm has a blog talking about how to customise annotation in Spring 4.3 application. I am curious to see how can I get the samething done using Genie. So it comes up with this project, which is literally a rewrite of Nicky Moelholm's spring43-custom-annotations with Genie

First let's take a look at the GreeterService code:

// Spring 4.3 Code
@BusinessService
public class GreeterService {
 
  @LocalizedMessage("greeterservice.greeting")
  private Message greetingMsg;
 
  public String sayHello(@NotNull String caller) {
    return greetingMsg.format(caller);
  }
 
}

In Genie version it is pretty much the same thing except we don't need the @BusinessService annotation:

// Genie Code
import org.osgl.$;

public class GreeterService {

    @LocalizedMessage("greeterservice.greeting")
    private Message message;

    public String sayHello(String caller) {
        return message.format($.notNull(caller));
    }

}

Note instead of using @NotNull annotation to declare the logic and then having a lot of code to implement it, we just use the handy shortcut to Object.requireNotNull to code our intention that the caller been passed in cannot be null. The aspect oriented implementation coded in the original project is way too complicated and have very bad runtime performance.

Now come to the LocalizedMessage code:

In the Spring 4.3 project:

// Spring 4.3 Code
@Autowired
@Retention(RetentionPolicy.RUNTIME)
public @interface LocalizedMessage {

  String value() default "";

}

In the Genie version:

// Genie Code
@InjectTag
@LoadValue(MessageLoader.class)
@Retention(RetentionPolicy.RUNTIME)
public @interface LocalizedMessage {

    String value() default "";

}

There is one more line @LoadValue(MessageLoader.class) found in the Genie version which declares how Genie should load the local Message instance: through the value loader class MessageLoader whose implementation is shown below:

// Genie Code
public class MessageLoader extends ValueLoader.Base<Message> {

    @Inject
    private MessageSource messageSource;

    @Override
    public Message get() {
        return new Message(value(), messageSource);
    }

}

This value loading mechanism is a unique feature of Genie and it help us to avoid coding the runtime dispatching logic using the InjectionPoint, in the original Spring 4.3 project, through the MessageConfig class:

// Spring 4.3 Code
@Configuration
public class MessageConfig {

  @Bean
  public MessageSource messageSource() {

    ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource();
    messageSource.setBasename("messages");

    return messageSource;
  }

  @Bean
  @Scope(scopeName = ConfigurableBeanFactory.SCOPE_PROTOTYPE)
  public Message message(InjectionPoint ip) {

    LocalizedMessage localizedMessage = AnnotationUtils
        .getAnnotation(ip.getAnnotatedElement(), LocalizedMessage.class);

    String resourceBundleKey = localizedMessage.value();

    return new Message(messageSource(), resourceBundleKey);
  }

}

Obviously the Genie version with customized value loading mechanism beat the InjectionPoint approach as

• There is no runtime overhead to lookup annotations for each method call
• The code is cleaner

There are some other classes created in the Genie version which is mainly to emulate corresponding class in Springframework, e.g.

• MessageSource
• LocaleContextHolder

They are all very simple and straightforward.

Finally here is the Application main class:

// Genie Code
public class Application {

    @Inject
    GreeterService greeter;

    public void run() {
        System.out.println("-- Default locale --");
        System.out.println(greeter.sayHello("Duke"));

        System.out.println("-- Danish --");
        LocaleContextHolder.set(new Locale("da", "DK"));
        System.out.println(greeter.sayHello("Duke"));

        System.out.println("-- Australia --");
        LocaleContextHolder.set(new Locale("en", "AU"));
        System.out.println(greeter.sayHello("Duke"));
    }

    public static void main(String[] args) {
        Genie genie = Genie.create();
        Application app = genie.get(Application.class);
        app.run();
    }

}

And the unit test case is exactly the same with the one in the original Spring 4.3 project except the Runner annotation is different.