A slots and signals variation for ActionEvent/ActionListener

ActionRouter.java

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.HashMap;
import java.util.Map;

/**
 * A routing table for Observers and Observables.
 *
 * Effectively allows routing of an {@link ActionEvent}. Charmingly reminiscent
 * of the classic "Signals and Slots" IPC mechanism, this allows the {@link ActionListener}
 * to be linked to a previously registered (or yet-to-be registered) proxy ActionListener.
 */
public class ActionRouter {
   private final Map<String, ActionListener> actionRoutes = new HashMap<>();

   /**
    * Register destination {@link ActionListener} (Observer) for {@code routeName}
    *
    * @param routeName key for this route
    * @param listener  destination listener for this route
    *
    * @see #createActionRoute(String)
    */
   public void acceptActionRoute(String routeName, ActionListener listener) {
      synchronized (actionRoutes) {
         actionRoutes.put(routeName, listener);
      }
   }

   /**
    * Register route (Observable) and return proxy {@link ActionListener}
    *
    * @param routeName key for this route
    *
    * @return a proxy ActionListener
    *
    * @see #acceptActionRoute(String, ActionListener)
    */
   private ActionListener createActionRoute(String routeName) {
      if (!actionRoutes.containsKey(routeName)) {
         synchronized (actionRoutes) {
            actionRoutes.put(routeName, null);
         }
      }
      return new ActionListener() {
         @Override
         public void actionPerformed(ActionEvent e) {
            if (actionRoutes.containsKey(routeName)) {
               ActionListener listener = actionRoutes.get(routeName);
               if (listener != null) {
                  listener.actionPerformed(e);
                  return;
               }
               JOptionPane.showMessageDialog(null, "Null route for: " + routeName, "CreateActionRoute", JOptionPane.INFORMATION_MESSAGE);
               return;
            }
            JOptionPane.showMessageDialog(null, "No action route for: " + routeName, "CreateActionRoute", JOptionPane.INFORMATION_MESSAGE);
         }
      };
   }
}