如何在jms接收器上应用观察者模式

Question

I have a java application that receives messages (using RabbitMQ). But I don't know how to apply the observer pattern to this. The incoming messages contain a position String and an incident String.

Application structure:

• adapters

  • MovementAPI -> class to handle incoming messages from RabbitMQ

• domain

  • Controller -> concrete Observer?
  • Message
  • (i) Observer
  • (i) Subject

I hope this is enough info.

Answer 1

The basic of of observer pattern says you will have a subject which will have broadcast to which registered objects (who are observers) will be notified

-- make a following interface which will be inplemented by your observers.

public interface Observer {
void update(String incident, String position);
}

---

make another interface which will be implemented by the Subject which has to broadcast the message

 public interface Subject {

    void registerObserver(Observer observer);

    void removeObserver(Observer observer);

    void notifyObservers();
}

lets have your class modified who's object will notify the other observer objects

public class YourBroadCastObjectData implements Subject {

private ArrayList<Observer> observers;
private String incident;
private String position;

public YourBroadCastObjectData() {
    // TODO Auto-generated constructor stub
    observers = new ArrayList<>();
}

@Override
public void notifyObservers() {
    // TODO Auto-generated method stub
    for (int i = 0; i < observers.size(); i++) {
        Observer observer = observers.get(i);
        observer.update(this.incident, this.position);
    }
}

@Override
public void registerObserver(Observer observer) {
    // TODO Auto-generated method stub
    observers.add(observer);

}

@Override
public void removeObserver(Observer observer) {
    // TODO Auto-generated method stub
    int i = observers.lastIndexOf(observer);
    if (i >= 0) {
        observers.remove(i);
    }

}

public void dataChanged() {
    notifyObservers();
}

public void setData(String incident, String position) {
    this.incident= incident;
    this.position= position;
    dataChanged();
}

public float getIncident() {
    return incident;
}

public float getPosition() {
    return position;
}



}

As far as I know you will have a asynchronous thread to get the data from the RabbitMQ Service to your application, in that thread have your subject notify all the objects.

you will have to implement the observer interface to your class who's object you want to act as observer. check some example online to see how observer pattern works.

Java provides in built support for observer pattern but it is concrete class which you have to inherit.

TO provide more flexible design you would better make your own pattern according to your need.

above code will help you push the data (Example.. incident and position), but you can also make pull pattern

As you would be implementing RabbitMQ you must have some data which is keep updating itself on server and your consumer code is hooked up to the producer of RabbitMQ service on server.

once you get the data from the consumer code you can have any class as subject (YorBroadCastObjectData) to implement SUbject and this object will send the data to observer objects. while making observer object give a reference to your subject's object that your observer object can register it self as a observer to the subject's object