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Java remote interface blocks the use of my GUI

I've given a bank application which I should modify so the balance of an account gets updated on every GUI screen. This should be done with RMI(Observable) in my example. I already made this work, at least, I'm almost certain about that.
There is a REMOTE interface called IBankingSession.
This REMOTE interface should have a method like setGUI(BankSessionController) or something like this. But, This isn't possible because the JavaFX parts aren't Serializable. The IBankingSession doesn't have any relationship to a GUI.
How can I link an instance of IBankingSession to this GUI? So I can update the GUI from this instance? It also feels weird to make a method like setGUI in a REMOTE interface. Because the GUI is of course, on the same screen as where the session is created.
I'm curious for some good idea's. Thanks in advance.
IBankingSession session = desk.logIn(tfAccount.getText(), tfPassword.getText());

First of all: you don't want to link your "remote" thing directly to your local clients that make use of it. That IBankingSession has no business knowing anything about the fact that your client wants to use JavaFx to put something on the user screens.
Instead, try something like this: define an interface that allows for callbacks (in other words: some kind of "push" model):
A client registers with the remote server; telling it: "I am interested in balance updates".
Then, upon a "balance" update, the remote service pushes that information to each client.
Now each client will be notified; and can then decide what to do with incoming updates; for example update some JavaFx UI component; or maybe, to log them into some persistent storage - giving you one mechanism that might be useful for a huge variety of different use cases.

You shouldn't be using observables at all, and certainly not over a network.
As far as RMI goes, you should strenously avoid anything in the nature of a client-side callback. There are firewall problems, latency problems, connectivity problems, ... every kind of thing that could cause your client to misfire.
You need to completely rethink this. It is not a viable design.

Swing - replacement for Qt signal/slots

In Qt GUIs it is very convenient use signals & slots - it decouple events passing. When I create some widget that throw signal, I don't have to know in advance who can get it, and later with connect I specify connections.
What is parallel in Java/Swing? Can you point to good resources on this issue?

If none of the existing EventListener implementations meet your requirements, you can create your own custom event. Every JComponent contains a field of type EventListenerList. You can use the approach outlined in the EventListenerList API to enable your custom JComponent subclass to fire your custom event.
Regarding the signal/slot mechanism, Swing has several ways to implement the observer pattern, outlined here.

This Event Listener tutorial goes through the basics of handling events with listeners.
Connecting your slot for a signal is analogous to adding your EventListener to an event-producing object.

How to control service visibility

Is there a way to control the visibility on services based on the filter of the listener?
I was disappointed to realize that the EventHook service can only control which bundles receive a ServiceEvent. Shouldn't it be which listeners receive the event? Instead of a collection of contexts it should be a collection of something similar to ListenerHook.ListenerInfo.
Is there another way I can control which listeners receive the events? I want to enforce a compulsory filter property to receive services, is it possible?

In Core 4.3 we add EventListenerHook which replaces EventHook. It will let
you filter at the listener level. This is currently implemented in the
Equinox 3.7 builds if you wish to experiment with it.
Quote of BJ Hargrave from an answer to the same question on osgi-dev maillist.

I think you are looking
org.osgi.framework.BundleContext.addServiceListener(ServiceListener, String)

Why people use message/event buses in their code? [closed]

Closed. This question is opinion-based. It is not currently accepting answers.
Closed 4 years ago.
Locked. This question and its answers are locked because the question is off-topic but has historical significance. It is not currently accepting new answers or interactions.
I think that you have heard of message/event buses, it's the single place when all events in the system flow. Similar architectures are found in computer's motherboards and LAN networks. It's a good approach for motherboards and networks as it reduces the number of wires, but is it good for software development? We don't have such restrictions as electronics does.
The simplest implementation of message bus/event bus can be like:
class EventBus {
void addListener(EventBusListener l}{...}
void fireEvent(Event e) {...}
}
Posting events is done with bus.fireEvent(event), receiving messages is enabled by bus.addListener(listener). Such architectures are sometimes used for software development, for example MVP4G implements similar message bus for GWT.
Active projects:
Google Guava EventBus
MBassador by Benjamin Diedrichsen
Mycila PubSub by Mathieu Carbou
mvp4g Event Bus
Simple Java Event Bus
Dormant/Dead projects:
Sun/Oracle JavaBeans InfoBus
https://eventbus.dev.java.net/ [Broken link]
It's just the popular Observer (Listener) pattern made 'globally' - each object in the system can listen to each message, and I think it's bad, it breaks the Encapsulation principle (each object knows about everything) and Single Responsibility principle (eg when some object needs to a new type of message, event bus often needs to be changed for example to add a new Listener class or a new method in the Listener class).
For these reasons I think, that for most software, Observer pattern is better than event bus. What do you think about event bus, does it make any good sense for typical applications?
EDIT: I'm not talking about 'big' enterprise solutions like ESB - they can be useful (what's more ESB offers much, much more than just an event bus). I'm asking about usefulness of using message bus in 'regular' Java code for object-to-object connection - some people do it, check the links above. Event bus is probably best solution for telephone-to-telephone communication or computer-to-computer communication because each telefone (or computer) in a network can typically talk to each other, and bus reduces the number of wires. But objects rarely talk to each other - how many collaborators one object can have - 3, 5?

I am considering using a In memory Event Bus for my regular java code and my rationale is as follows
Each object in the system can listen to each message, and I think it's
bad, it breaks the Encapsulation principle (each object knows about
everything)
I am not sure if this is really true, I class needs to register with the event bus to start with, similar to observer pattern, Once a class has registered with the Event Bus, only the methods which have the appropriate signature and annotation are notified.
and Single Responsibility principle (eg when some object needs to a
new type of message, event bus often needs to be changed for example
to add a new Listener class or a new method in the Listener class).
I totally disagree with
event bus often needs to be changed
The event bus is never changed
I agree with
add a new Listener class or a new method in the Listener class
How does this break SRP ?, I can have a BookEventListener which subscribes to all events pertaining to my Book Entity, and yes I can add methods to this class but still this class is cohesive ...
Why I plan to use it ? It helps me model the "when" of my domain ....
Usually we hear some thing like send a mail "when" book is purchased
we go write down
book.purchase();
sendEmail()
Then we are told add a audit log when a book is purchased , we go to the above snippet
book.purchase();
sendEmail();
**auditBook();**
Right there OCP violated
I Prefer
book.purchase();
EventBus.raiseEvent(bookPurchasedEvent);
Then keep adding handlers as needed Open for Extension Closed for Modification
Thanks

Some people like it because it is the embodiment of the Facade pattern or Mediator pattern. It centralizes cross-cutting activities like logging, alerting, monitoring, security, etc.
Some people don't like it because it is often a Singleton point of failure. Everyone has to know about it.

I use it heavily in JavaScript. There can be so many various widgets that all need to do some sort of action whenever something else happens -- there is no real hierarchy of ownership of objects. Instead of passing references of every object to every object, or just making every object global, when something significant happens inside a particular widget, I can just publish "/thisWidget/somethingHappened" -- instead of filling that widget with all kinds of code specific to the API of other widgets. The I have a single class that contains all the "wiring", or "plubming" as they like to call it in the Java Spring framework. This class contains references to all of my widgets, and has all of the code for what happens after each various event fires.
It is centralized, easy to access and maintain, and if one thing changes or I want a new process to occur on a specific event, I don't have to search through every single class/object/widget to try to find out where something is being handled. I can just go to my "operator" class -- the one that handles all the "wiring" when a particular event happens, and see every repercussion of that event. In this system, every individual widget is completely API agnostic of the other widgets. It simply publishes what has happened to it or what it is doing.

I'm having trouble understanding what you're really asking in your question. You give an example of a simple event bus which is actually just Observable with a different name, then you say;
For these reasons I think, that for
most software, Observer pattern is
better than event bus. What do you
think about event bus, does it make
any good sense for typical
applications?
..but given your example, they are the same. This makes me wonder if you have ever used something like a Enterprise Service Bus. At a base level an ESB logically does the same thing as the observer pattern, but commercial products add much, much more. Its like an event bus on steroids. They are complicated software products and offer;
Message pickup
Generate events by listening to various endpoints. The endpoint can be a listener (such as a HTTP server), a messaging system (such as JMS), a database or pretty much anything else you want.
Message routing
Take your event and send it to one/many endpoint. Routing can be pretty smart, the bus might route the message depending on the message type, the message contents or any other criteria. Routing can be intelligent and dynamic.
Message Transformation
Transforms your message into another format, this can be as simnple as from XML to JSON or from a row on a database table to a HTTP request. Transformation can occur within the data itself, for example swapping date formats.
Data Enrichment
Adds or modifies data in your message by calling services along the way. For example if a message has a postcode in it the bus might use a postcode lookup service to add in address data.
..and lots, lots more. When you start looking into the details you can really start to see why people use these things.

Because it can be an important step in the way to decouple the application modules to a service based architecture.
So in your case if you have not the intention to decouple the modules of your application into isolated services then the native implementation of the Observer pattern will make it a simpler solution.
But If you want to build lets say a micro-services architecture the event-bus will allow to get the benefits of this architecture style so you could for instance update and deploy just some part of your application without affect others, because they are just connected through the event-bus.
So the main question here is the desired level of application components decoupling.
Some references about it:
http://microservices.io/patterns/data/event-driven-architecture.html
http://tech.grammarly.com/blog/posts/Decoupling-A-Monolithic-Server-Application.html

A good analogy is that of a telephone exchange, where every handset can dial to every other handset. A compromised handset can tune into other conversations. Program control flows like wires(cyclomatic complexity anyone!) This is similar to the requirement of having a connection/physical medium between two end points. This is So for N handsets instead of having NC2 (Combinatorial logic) flows for every new handset we tend to get N flows.
A reduction in complexity implies easy to understand code. Lets start with the prominent points you have highlighted: 1. Global knowledge 2. Intrusive modifications.
Global Knowledge: Consider message event to be an envelop. From event handler/sender perspective there is no data being exposed, it is seeing an envelop (unless an derived class tries to do some inspection using 'instanceof' checks). In a good OOP design, this would never occur.
Intrusive modifications: Instead of having a event specific listener approach, one can use a global event handling approach. As such we have a global event type (on which data is piggy backed and down-casted). This is much like the PropertyBeanSupport model in Java. With a single event type we are required to have a single sender and listener types. This implies you need not modify the bus/listeners every time you see something new. The ugly down-casting can be soothened using Adapter pattern (Please don't start that another level of redirection quote!). Programmers can write assembly in any language. So need for commonsense and smartness can not be substituted. All I intend to state is it can be a effective tool.
The actual event receivers can use the listeners (composition/proxy) easily. In such a Java code base, listeners would look like stand alone inner class declarations (with unused warning being flagged in certain IDEs). This is akeen to two players on the beach playing a ball game, the players don't react until they see the ball.
'#duffymo' points out another interesting aspect: 'Single point of failure'. This would/can in theory effect any object residing in memory(RAM) and not specific to MessageHandlers.

As a practical example, our app sync's with a web service every x number of minutes, and if any new data is received, we need to update the GUI. Now, because the SyncAdapter runs on a background thread, you can't simply point to a textview and modify its properties, you have to bubble up an event. And the only way to make sure you catch that event is if you have a shared (static,singleton) object passing that event around for subscribers to handle.

Java equivalent of Cocoa NSNotification?

I am writing a Java application using SWT widgets. I would like to update the state of certain widgets upon a certain event happening (for example, updating the data model's state).
Is there something in Java similar to Cocoa's NSNotificationCenter, where I can register an object to listen for notification events and respond to them, as well as have other objects "fire off" a notification?

Ok, suppose that for example, you want parts of your program to be notified when your Loader starts a scan, and when it finishes a scan (don't worry about what a Loader is, or what a scan is, these are examples from some code I have lying around from my last job). You define an interface, call it "ScanListener", like
public interface ScanListener
{
public void scanStarted();
public void scanCompleted();
}
Now the Loader defines a method for your other code to register for callbacks, like
public void addScanListener(ScanListener listener)
{
listeners.add(listener);
}
The Loader, when it starts a scan, executes the following code
for (ScanListener listener : listeners)
{
listener.scanStarted();
}
and when it finishes, it does the same thing with listener.scanCompleted();
The code that needs to be notified of these events implements that interface (either themselves, or in an internal class), and calls "loader.addScanListener(this)". Its scanStarted() and scanCompleted() methods are called at the appropriate times. You can even do this with callbacks that take arguments and/or return results. It's all up to you.

What sort of notifications are you looking for? If all you want is for one object to be able to tell anybody else "hey, I've changed, update accordingly", the easiest way is to use the existing Observer interface and Observable class. Or write your own with an interface that defines what you want to get called on the listeners from the one that's changed.

There's no pre-existing per-process service that dispatches events in java that's equivalent to the default NSNotificationCenter. In java, the type of the event is specified by the event object being a particular type (which also means that the notification method depends on that type) rather than using a string. Prior to generics, writing a general event dispatcher and receiver that is also typesafe isn't really possible (witness the proliferation of *Event classes and *EventListener interfaces in the AWT and Spring libraries).
There are some facilities for event dispatch. As Paul mentioned, there's java.util.Observable, which as you point out, requires subclassing. There's also java.beans.PropertyChangeSupport, which could be useful depending on your situation.
You could also write one yourself. The source for PropertyChangeSupport is likely available in the openjdk, and you could look at the abandoned Apache Commons Event project. Depending on your needs, you may have to worry about stuff like threading, seralization, memory leaks (ensuring deregistration or using weak references), and concurrent modification (iterate over a copy of your list of listeners, as a listener may decide to unregister itself in response to a change).
Now that generics exist in Java, a generic event dispatch library would be possible; however, I haven't come across any. Anyone?

There's actually a facility built in to Java that does exactly what you want, but it's not something you may have considered, and, to be honest, it is likely a bit heavyweight for what you want.
That said, however, it does exist.
It's JMX.
You create MBeans, and then others can register for events from those MBeans. The MBean can then send of a Notification.
I personally wouldn't consider using it for this case (I'd just pound out my own), but the facility is there and it well defined and documented.

Not Java, but the IPython project has a notification center written in Python here that you could use as a template for a Java version.

In Java this would be a provider firing notifications to its listeners. But Java does not offer the loose coupling you get with Cocoa's NSNotification because in Java providers and subscribers must have references to each other. Compare for this chapter 18 in "Learn Objective-C for Java Developers".

There is an implementation of IOS NSNotificationCenter in Java.
You can find sources code in :
This Github project