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Java - Swing UI separate socket logic

I become desperate, I develop a simple multi-user chat in Java based on the client-server principle. I already wrote a basic multi-threaded server application and it works great. My problem is the client on the basis of the Swing GUI Toolkit. A basic UI with a runtime loop for receiving messages in the background. My problem is that I want to separate the socket logic from the UI, this means that in the best case I've two different classes one for the socket runtime loop and another to manage the UI. Because of the problem, that the runtime loop must notify/add messages to the UI, they depend on each other.
MessengerView is my main class which contains the swing ui and all depended components. At the moment this class contains also the socket logic, but I want to extract them to an external class.
ClientRuntime the class which should hold the socket logic...
My question is, how could I separate them and how could I connect them? For example I tried swing-like events with registering of methods like this:
addListener(MessageArrivedListener listener);
emitMessageArrivedEvent(String message);
The problem is, that it is very confusing if the count of events raises! As already said my second options is to hold socket logic and ui design in one class, but I think it's a bad idea because it makes it very hard to write unit tests for it or to find bugs...
In my time with C++ I used sometimes friend-classes for this issue, because this makes it possible to access class members of other classes! But this solution is often also very confusing and I found no such option for Java.
So are there any other possibilities to hold the connection between the swing widgets and the socket logic, without storing them in the same class (file)?

how could I separate them and how could I connect them?
Connect them with BlockingQueue - this the first choice when choosing ways to connect threads.
ClientRuntime class must start 2 threads: one takes requests from the blocking queue and sends them to the server, and the second constantly reads the messages from the server through the socket and sends them to the UI thread. The UI thread has already input blocking queue for messages: it is accessed by SwingUtilities.invokeLater(Runnable);. The ClientRuntime class does not access UI queue directly: it calls a method from MessengerView and passes what it received from the socket, a binary array or json string, and that UI method converts it to some Runnable which actually updates the UI.

they depend on each other
Well, they don't really. The "socket" layer only cares about been started, running, posting some messages and stopping.
How all that actually get done/handled it doesn't care about, it just "starts" when told, processes input/output messages, posts notifications and "stops" when asked to.
This is basically an observer pattern, or if you prefer, a producer/consumer pattern.
So the socket layer needs to define a "protocol" of behaviour or contract that it's willing to work with. Part of that contract will be "how" it generates notifications about new messages, either via an observer or perhaps through a blocking/readonly queue - that's up to you to decide.
As for the UI, it's a little more complicated, as Swing is single threaded, so you should not block the UI with long running or blocking operations. This is where something like a SwingWorker would come in handy.
It basically acts a broker between the UI and the mechanism made available by the socket layer to receive messages. Messages come from the socket layer into the SwingWorker, the SwingWorker then publishes them onto the UI's event thread which can then be safely updated onto the UI
Maybe start with Concurrency in Swing and Worker Threads and SwingWorker
My question is, how could I separate them and how could I connect them? For example I tried swing-like events with registering of methods like this:
The problem is, that it is very confusing if the count of events raises!
I don't think so (IMHO). What you want to do is focus on the "class" of events. For example, from the above, you have "life cycle" events and you have "message" events. I'd start by breaking those down into two separate interfaces, as those interested in "message" events probably aren't that interested in "life cycle" events, this way you can compartmentalise the observers.
The important concept you want to try and get your head around is the proper use of `interfaces to define "contracts", this becomes the "public" view of the implementations, allowing you devise different implementations for different purposes as you ideas change and grow. This decouples the code and allows you to change one portion without adversely affecting other parts of the API

Exclusive access established by another Thread Java smartcardio

All,
I have appreciated many helpful answers on this site but I have found a need to post my first question (if you notice anything to be improved in my post let me know).
I have a modest sized Java program with GUI that is acting as a "middleman" and controller. On one end of the information flow it sends and receives data via an HTTP server. On the other it is interacting with an API where data is ultimately exchanging with a SmartCard. In the "middle" is the GUI, logging, and some other features.
There is also a feature (initiated via the GUI) to occasionally load an update to the SmartCard. Otherwise exchanges with the SmartCard are initiated over HTTP.
The problem is when switching between these 2 modes (communicating http to smartcard and then switching to loading the update or vice versa).
When I do that I have concluded I run into the problem of
CardException: Exclusive access established by another Thread
as thrown by sun.security.smartcardio
Searching the web shows the code that exception appears to come from is
void checkExclusive() throws CardException {
Thread t = exclusiveThread;
if (t == null) {
return;
}
if (t != Thread.currentThread()) {
throw new CardException("Exclusive access established by another Thread");
}
}
My first thought was I needed to instantiate the SmartCard API each time I need it (and then set it back to null) instead of once for the entire program like I had initially.
This works for the exchanges over http and I figure it is because each request to the handle() method is a new thread.
In the GUI the update is initiated by an ActionEvent which makes an instance of a CardUpdate. Inside that class then gets an instance of the SmartCard API.
I thought maybe I'd have better luck if when actionPerformed triggered I put the actions on a different, temporary, thread. So far, no.
The closest I got was using something like:
SwingWorker worker = new SwingWorker<ImageIcon[], Void>() {
as found at on Sun's website
Using that I could do an update and then go back to http exchanges but I couldn't do another update (per the one time use stipulation of SwingWorker)
I then tried making multiple SwingWorker as needed doing something like
private class GUICardUpdate extends SwingWorker<Integer, Void > {
but then I was back to my original problem. I have also tried to just do a simple additional thread off the GUI class in this fashion:
public class GUI extends javax.swing.JFrame implements ActionListener, Runnable
but this is no different.
Maybe I don't understand threads well enough or maybe I am overlooking something simple. Anyone have any ideas?
Thanks!

As far as I got you are using javax.smartcardio package (directly or indirectly) to work with your card. Some thread (created by you or by the framework you are probably using on top of javax.smartcardio) invoked beginExclusive() method on the Card instance to ensure exclusive access to the card.
The exclusive access is necessary as treatment of the data kept on the IC cards is state-depended, so the proper selection of data files and reading of their records requires the actions of application layer not to be interfered with actions of some other application or thread. For this purpose these three Card interface methods beginExclusive(), endExclusive() and checkExclusive() exist.
So you should check your(framework) code if it calls beginExclusive() and then doesn't call endExclusive().

create a server application having gui

I have to create an application having a GUI. my application has to work as a server. When it starts, it has to accept all the incoming connection and write the output in a JTextArea. my problem is where I have to create the ServerSocket ss = new ServerSocket(port_number) and the method ss.accept in the way I can accept connections. I tried to create in the main constructor of my gui but being ServerSocket anI/O request the gui stucks.some idea to resolve the solution?
I create in the constructor of my GUI:
SwingUtilities.invokeLater(new Runnable(){public void run(){connection();}});
where connection() is the method where I create the serversocket and accepts call

You should create a separate thread to wait/handle the network connections.
When a new connection comes in read the data and pass them to the EDT to update the GUI.
This way the GUI will be responsive.
You should read about MVC Pattern threads. If you Google there is an abundance of articles to study
UPDATE:
Your code here is wrong.
SwingUtilities.invokeLater(new Runnable(){public void run(){connection();}});
You are handling the connection from the EDT thread.
You should use this to update the GUI and not to call the network I/O code.

The IO logic must be in (at least one) separate background thread. Each time something must be printed to the text area from one of those background threads, they should do it using SwingUtilities.invokeLater(), to make sure that the Swing components are only accessed from the event dispatch thread.
That said, I don't think it's a very good idea to have a GUI for a server. Why don't you simply write in a log file, and use any text editor to see what the server received. Or write the GUI of the server as a client of this server?

IO thread alert GUI thread if error occures

I have a client/server question that i am trying to figure out the best solution for.
If a client ever gets disconnected from the server, for any reason, i would like a way for the input output thread to alert the gui thread that something went wrong, and thus have the gui thread print an error and gracefully handle it (probably drop back out to the login gui). After the initial gui thread is created, the client could change to any number of guis, depending on what he is doing, so I am thinking i need a way to dynamically see what gui is currently being run.
The way that i was thinking of doing this so far:
1) Create an object that creates and shows every gui. So instead of calling invokeLater...SomeGui.CreateAndShoGui()... we would have this object be responsible for doing that, ie GuiObject.showSomeGui();
2) Have each gui implement an interface, which will insure there is a method that, when called, will gracefully shutdown this gui when we have lost connection to the server.
3) Have a thread that monitors the IO thread and the gui object. If something goes wrong on the IO thread, the IO thread will close down and notify the monitoring thread that we have lost connection the server. The monitoring thread could then alert any open guis (from the gui object) that we have lost connection and that it needs to shut down.
I have just started thinking about this, and so far this is the best solution i have come up with. Does this seem like a reasonable solution that wont add too much complexity to the code? Or can anyone recommend a solution that would be simpler for people reading the code to understand?
Thanks
EDIT:
The other option i am toying with is having an object on the IO thread, that also gets passed to each new gui as it is opened. This object will give the currently opened guis reference back to the io thread, so that the io thread can alert it if something goes wrong. I am leaning against this solution though, because it seems like it would be easier to read if you had one object that was dedicated to get this working (like the above solution), instead of passing some obscure object to each gui.

Let me just go through each of your ideas:
1) Bad idea - you are tying your whole application together through a single object. This makes maintainability difficult and is the antithesis of modularity.
2) This is the way to go IMHO. Since it seems that each gui has unique logic in a failure scenario then it stands to reason that the object that best understands what to do would be the gui object itself.
Another version of this idea would be to create an adapter for each gui to put this failure logic into. The advantage would be you have one less dependency between your application framework and your gui. The disadvantage is that this is an extra layer of complexity. If your gui is already pretty coupled to your application then I would choose the interface method. If you want to reuse your guis in another application then the adapter way could help facilitate that.
3) This complements #2 nicely. So let me get this straight - you would have 3 threads: the IO thread, the monitor thread, and the UI thread. I don't know if you need the monitor thread. From what you were saying the IO thread would be able to detect a connection problem by itself (probably because some form of IOException was caught). When a connection problem is discovered the IO thread is not busy since it is just going to shut itself down soon so it might as well just have the responsibility of notifying the guis that there was a problem. The guis should have their interface method called on the UI thread anyways so the IO thread is just calling a bunch of invokeLater() calls (or asyncExec() calls for SWT) and then the IO thread can just shut itself down.
4) (Your Edit) You are basically describing the Visitor pattern. I do not think this is a good solution because the call is from the IO thread to the gui and not the other way around. I am not sure how passing a visitor object around will help in this case.
One final thought. If you make your interface generic (not gui specific) then you can apply this pattern to other resources. For instance you may want to flush your user credentials when you lose connection (since you talked about going to the login screen again). That isn't really gui logic and should not be done from a gui class.
Edit: I would use an event model. Let's say you create a interface like this:
public interface ConnectionFailureListener {
void handleConnectionFailure(); // Add an event object if you need it
}
You could then have registration methods in some object (maybe the Runnable for the IO thread or somewhere else that is convenient for you). These methods would be pretty standard:
public void addConnectionFailureListener(ConnectionFailureListener l) {}
public void removeConnectionFailureListener(ConnectionFailureListener l) {}
When you show a gui on the screen you would add it to your registration object and when you close the gui you would remove it from the registration object. You can add other types of objects as needed - for example when you log in you can add a listener for your credential system and remove it again when log out is processed.
This way when you have a failure condition you simply loop through the currently registered listeners and the listener does its thing.

Java Swing design pattern for complex class interaction

I'm developing a java swing application that will have several subsystems. For all intents and purposes, let's assume that I am making an internet chat program with a random additional piece of functionality. That functionality will be... a scheduler where you can set a time and get a reminder at that time, as well as notify everyone on your friend list that you got a reminder.
It makes sense to organize this functionality into three classes: a GUI, a ChatManager, and a Scheduler. These classes would do the following:
GUI - Define all of the swing components and events
ChatManager - Create a chat connection, send and receive messages, manage friend list
Scheduler - Monitor system time, send notifications, store a file to remember events between sessions
For the program to work, each of these classes must be capable of communicating with the other two. The GUI needs to tell the ChatManager when to send a message and tell the Scheduler when to start monitoring. The ChatManager needs to display messages on the GUI when they're received, and finally, the Scheduler needs to both notify the GUI when it's finished, and send a status update or whatever to the ChatManager.
Of course, the classes as described here are all pretty simple, and it might not be a bad idea to just let them communicate with each other directly. However, for the sake of this question, let's assume the interactions are much more complex.
For example, let's say we can register a particular event with the scheduler instead of a particular time. When sending a message, I went to send it to the user, store it in a log file, create an event object and pass it to the scheduler, and handle any exceptions that might be thrown along the way.
When communication becomes this complex, it becomes difficult to maintain your code if communication with these classes can be happening in many different places. If I were to refactor the ChatManager, for example, I might also need to make significant chaneges to both the GUI and Scheduler (and whatever else, if I introduce something new). This makes the code difficult to maintain and makes us sleep-deprived programmers more likely to introduce bugs when making changes.
The solution that initially seemed to make the most sense is to use the mediator design pattern. The idea is that none of these three main classes are directly aware of each other, and instead, each is aware of a mediator class. The mediator class, in turn, defines methods that handle communication between the three classes. So, for example, the GUI would call the sendMessage() method in the mediator class, and the mediator would handle everything that needed to happen. Ultimately, this decouples the three main classes, and any changes to one of them would likely only result in changes to the mediator.
However, this introduces two main problems, which ultimately resulted in me coming here to seek feedback. They are as follows:
Problems
Many tasks will need to update the GUI, but the Mediator isn't aware of the components. - Suppose the user starts the program and enters their username/password and clicks login to login to the chat server. While logging in, you want to report the login process by displaying text on the login screen, such as "Connecting...", "Logging in...", or "Error". If you define the login method in the Mediator class, the only way to display these notifications is to create a public method in the GUI class that updates the correct JLabel. Eventually, the GUI class would need a very large amount of methods for updating its components, such as displaying a message from a particular user, updating your friend list when a user logs on/off, and so on. Also, you'd have to expect that these GUI updates could randomly happen at any time. Is that okay?
The Swing Event Dispatch Thread. You'll mostly be calling mediator methods from component ActionListeners, which execute on the EDT. However, you don't want to send messages or read/write files on the EDT or your GUI will become unresponsive. Thus, would it be a good idea to have a SingleThreadExecutor available in the mediator object, with every method in the mediator object defining a new runnable that it can submit to the executor thread? Also, updating GUI components has to occur on the EDT, but that Executor thread will be calling the methods to update the GUI components. Ergo, every public method in the GUI class would have to submit itself to the EDT for execution. Is that necessary?
To me, it seems like a lot of work to have a method in the GUI class to update every component that somehow communicates with the outside, with each of those methods having the additional overheard of checking if it's on the EDT, and adding itself to the EDT otherwise. In addition, every public method in the Mediator class would have to do something similar, either adding Runnable code to the Mediator thread or launching a worker thread.
Overall, it seems like it is almost as much work to maintain the application with the Mediator pattern than to maintain the application without it. So, in this example, what would you do different, if anything?

Your GUI classes will end up with many methods to keep it up to date and that is fine. If it worries you there is always the option of breaking up the GUI into sub GUIs each with a different functionality or a small set of related functionality. The number of methods will obviously not change, but it will be more organised, coherent and decoupled.
Instead of having every method in your GUI create a Runnable and use SwingUtilities.invokeLater to put that update on the EDT I'd advise you to try out another solution. For my personal projects I use The Swing Application Framework (JSR296) which has some convenient Task classes for launching background jobs and then the succeed method is automatically on the EDT thread. If you cannot use this you should try and create your own similar framework for background jobs.

Here, a partial answer to you design questions...
It looks like you want to have loose coupling between your components.
In your case, I would use the mediator as a message dispatcher to the GUI.
The ChatManager and the Scheduler would generate UpdateUIMessage.
And I would write my GUI that way
public class MyView {
public void handleUpdateMessage(final UpdateUIMessage msg){
Runnable doRun = new Runnable(){
public void run(){
handleMessageOnEventDispatcherThread(msg);
}
};
if(SwingUtilities.isEventDispatcherThread()){
doRun.run();
} else {
SwingUtilities.invokeLater(doRun);
}
}
}
So you have only one public method on your GUI, which handles all the EdT stuff.
If you want to have a loose coupling between the GUI and the other components (meaning : you do not want the GUI to know all the API of the other components), the GuiController could also publish ActionMessage (on a specific Thread?), which would be dispatched by the mediator to the other components.
Hope it helps.

Well, I will change the world you are working with. You have 3 classes and each of them is just observer of the chat-world. The MVC is the way how to deal with your problem. You had to create Model for your world, in this case chat program. This model will store data, chat queue, friend list and keep eye on consistency and notify everybody interested about changes. Also, there will be several observers which are interested in state of world and are reflecting its state to user and server. The GUI is bringing visualization to friends-list and message queue and reacts on their changes. The Scheduler is looking about changes in scheduled tasks and update model with their results. The ChatManager will be better doing its job in several classes like SessionManager, MessageDispatcher, MessageAcceptor etc. You have 3 classes with empty center. Create center and connect them together using this center and Observer Pattern. Then each class will deal only with one class and only with interesting events. One GUI class is bad idea. Divide to more subclasses representing logical group (view of model). This is the way how to conquer your UI.

You might want to look at a project that originally started as a MVC framework for Flex development. PureMVC has been ported to many programming languages meanwhile, including Java. Though it is only in a alpha status as of writing this!