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How to use Jpa Hibernate Lifecycle Events Feature

Consider two possibilities to understand a typical usage and its not about Validation its all about Integration.
   
     1. You wrote a Bug Tracking Application and deployed it at your client, client has a new requirement that when a new bug is created it wants to send its information to other internal System via Web Service.

   2. You wrote an Enterprise Application and a new features requires that when a new Product is added to database via JPA Hibernate its details should be sent to other departments via Web Service call.

And this is where the feature kick-ins.
  We need to design and implement the capability with these features
  1. Scalable (should be able to use separate threat to do its job).
  2. Simple Design and Usable.
  3. Extendable i.e. No procedural junk code.
Consider following design and Code snippet where Manufacturer and Product are JPA Entities and PartnerXNotifier and PartnerYNotifier are Web Service Clients.
   





@EntityListeners({EventListener.class})
@Entity
public class Product implements Serializable {

}


@EntityListeners({EventListener.class})
@Entity
public class Manufacturer implements Serializable {
}

public class EventListener {

    @PrePersist
    public void prePersist(Object object) {
        EventObserver.getIntance().prePersist(object);
    }

    @PostPersist
    public void postPersist(Object object) {
        EventObserver.getIntance().postPersist(object);
    }

    @PreUpdate
    public void preUpdate(Object object) {
        EventObserver.getIntance().preUpdate(object);
    }

    @PostUpdate
    public void postUpdate(Object object) {
        EventObserver.getIntance().postUpdate(object);
    }

    @PreRemove
    public void preRemove(Object object) {
        EventObserver.getIntance().preRemove(object);
    }

    @PostLoad
    public void postLoad(Object object) {
        EventObserver.getIntance().postLoad(object);
    }
}

public class EventObserver {

    private Map<Class, Set<Handler>> map = new HashMap<Class, Set<Handler>>();
    private static final EventObserver observer = new EventObserver();

    private EventObserver() {
    }

    public static EventObserver getIntance() {
        return observer;
    }

    public void clear() {
        map = new HashMap<Class, Set<Handler>>();
    }

    public void loadPropertiesFileOnChange() {
        // Todo  entity_listener.properties from classpath
        // sample file contents
        // Product=com.company.project.PartnerXNotifier
       // Manufacturer=com.company.project.PartnerYNotifier
    }
    public void registerHandler(Class clazz, Handler handler) {
        Set<Handler> handlers = map.get(clazz);
        if (handlers == null) {
            handlers = new HashSet<Handler>();
        }
        handlers.add(handler);
        map.put(clazz, handlers);
    }

    public void prePersist(Object object) {
        Set<Handler> set = map.get(object.getClass());
        for (Handler handler : set) {
            handler.prePersist(object);
        }
    }

    public void postPersist(Object object) {
        Set<Handler> set = map.get(object.getClass());
        for (Handler handler : set) {
            handler.postPersist(object);
        }
    }

    public void preUpdate(Object object) {
    }

    public void postUpdate(Object object) {
    }

    public void preRemove(Object object) {
    }

    public void postLoad(Object object) {
    }
}


public interface Handler {
    public void prePersist(Object object);
    public void postPersist(Object object);
    public void preUpdate(Object object);
    public void postUpdate(Object object);
    public void preRemove(Object object);
    public void postLoad(Object object);
}

public class PartnerXNotifier implements Handler {
    public void prePersist(Object object) {
        // Call the webservice of the partner and pass the object.
    }
    public void postPersist(Object object) {
    }
}

public class PartnerYNotifier extends AbstractHandler {
    @Override
    public void preRemove(Object object) {
        // update partnery webservice 
    }
}

public abstract class AbstractHandler implements Handler {
    public void prePersist(Object object) {}
    public void postPersist(Object object) {}
    public void preUpdate(Object object) {}
    public void postUpdate(Object object) {}
    public void preRemove(Object object) {}
    public void postLoad(Object object) {}
}




Above design can significantly improve by introducing
  •    Generics in Handler
  •    ThreadExecutor in EventObserver
  •    Properly implementing loadPropertiesFileOnChange() to load properties file from multiple    classpath locations
Hope make sense and opens door for seamless integration with other Systems.

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