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Vaadin 8 : reload grid with data from server every 1min

I am trying to have a auto refresh feature for the grid which basically, updates the grid with latest data from the server every 'n' seconds.
I was able to implement the PollListner whenever the user enables Auto-Refresh.
UI ui= TestUI.getCurrent();
Boolean value = isRefreshChkBox.getValue();
PollListener listener = e -> {
explorer.reloadUI();
};
if (value) {
String refreshRateValue = refreshRateTxtField.getValue();
int refreshRate = Integer.valueOf(refreshRateValue);
int millis = (int) TimeUnit.SECONDS.toMillis(refreshRate);
absUI.setPollInterval(millis);
absUI.addPollListener(listener);
} else {
absUI.setPollInterval(-1);
absUI.removePollListener(listener);
}
With the above code, I add PollListener everytime autorefresh is enabled and I remove it on disable.
I found similar question here VAADIN 7: What is the simplest way to refresh a Vaadin View in 5 minute intervals?
But what I want to understand, is there a better approach to achieve a simple usecase AutoRefresh UI?? where should PollListener be implemented?? I thought of creating PollListener once for the view and just update the PollInterval everytime user changes the refresh rate.
Any pointers on which approach is better or is there completely new concept in Vaadin to achieve this?
TIA

See the correct Answer by Leif Åstrand. I will add a bit of discussion, and a complete example app using both Polling and Push.
Vaadin 8 has two ways to automatically update the display of information without the user making a gesture: Polling & Push.
Polling
In Vaadin 8’s Polling feature, you set a polling interval of milliseconds on your UI subclass. The default value of -1 disables Polling.
myUI.setPollInterval( ( int ) TimeUnit.MINUTES.toMillis( 1 ) ); // Specify milliseconds for polling interval.
When enabled, the Vaadin JavaScript library installed in the user’s web browser checks in with the Vaadin server. Being a PollNotifier, the UI checking-in causes an event to be fired on the server-side.
If you define a class that implements the PollListener interface, your instance will have its poll method invoked.
Upon registering your PollListener. get back a Registration object. That object provides a remove method to unregister your listener, if need be.
You have your choice of defining your PollListener using lambda syntax, an anonymous inner class, or a separately-defined class.
Registration registration = this.addPollListener( new UIEvents.PollListener() {
#Override
public void poll ( UIEvents.PollEvent pollEvent ) {
System.out.println( "TRACE - PollListener::poll running. " + Instant.now() );
…
}
} );
Or, lambda syntax:
Registration registration = this.addPollListener( ( UIEvents.PollListener ) pollEvent -> {
System.out.println( "TRACE - PollListener::poll running. " + Instant.now() );
…
} );
During this invocation, your code can register a Runnable to be invoked at a convenient time with your UI subclass.
That Runnable does the work of updating widgets contained in your UI subclass. Remember to never access or modify widgets from a background thread. You may get away with it, or you may cause terrible things to happen. Be safe: Always call UI::access to pass a Runnable that accesses the widgets. That Runnable will be run on the main user-interface thread of your web app, the thread in charge of your UI subclass instance.
getUI().access( new Runnable() {
#Override
public void run ( ) {
subscriber.refresh( new ArrayList <>( statusList ) ); // Copy the list in case the `Grid` modifies it, such as sorting.
}
} );
Pros
The upside of using the Polling feature is that the programming you must do is simpler than with Push (discussed below). Polling is likely a better route to take when learning about automated non-user-generated updates.
One simple aspect is that each instance of your UI subclass is in charge of its own polling, choosing if and when to do polling and controlling how often to poll. Each UI subclass instance calls its own setPollInterval method. More polling may be nice for the user, but the chattiness increases network traffic, thereby making your network admin cranky. So you can tune the frequency by UI subclass instance. Remember that not only does each user have their own UI subclass instance, but also, Vaadin 8 is capable of multi-window/tab apps. One web app in each web browser can have multiple windows/tabs open, each running their own instance of the same or different UI subclasses.
Cons
One downside aesthetically is that polling breaks the request-response elegance of the HTTP design. While this is a pet-peeve of mine, that ship has sailed long ago, so I'll not waste bytes here ranting about using a document-delivery system as an interactive client-server app architecture.
A more practical downside is unnecessary traffic on the network. If you are able to use Push via WebSocket or Webpush, then an open connection is maintained between client and server with very little traffic all the while until the server generates an event to be communicated to the client. But be aware that WebSocket is easily defeated by firewalls & proxies, and Webpush may not be implemented/supported, in which case the Push implementation in Vaadin (the Atmosphere Framework library by async-io.org) may fall back to polling techniques.
Another downside is inefficiency of each client doing its own repeated polling and each triggering a separate execution on the server-side such as the search for fresh data in the database. If you have many clients all consuming the same set of immutable objects, then Push can be more efficient doing a single search for fresh data and delivering the same bunch of data objects to all the clients.
Push
The combination of Vaadin with Atmosphere (linked above) vastly simplifies using Push technology in your web app. Nevertheless, it is a bit more complicated with more moving parts than seen with the Polling feature.
Firstly, enable Push with the #Push annotation on your UI subclass.
Then schedule the firing of an event every minute using a ScheduledExecutorService. Set up that executor with a ServletContextListener. See example code below for all this.
Pros
Push can be quite efficient in terms of network traffic able to use WebSocket technology or Webpush, as mentioned above.
Cons
Unfortunately WebSocket can be defeated by firewalls & proxies. And Webpush is new and may not be widely supported. In this case, Vaadin/Atmosphere may fall-back to using a polling approach.
Another downside is that the coding is a bit more complex. A programmer new to this work may take a while to grasp the various moving pieces.
You need a background thread on the server-side to track the time, in our case firing every minute. The modern approach to that is using a ScheduledExecutorService to handle the threading and firing schedule.
To setup that executor service, you will need to implement a ServletContextListener as discussed below.
Be aware that some of the push approaches, especially WebSocket, involve maintaining an open network connection. So this consumes resources such as port numbers on your server machine.
Example app
I built a complete working example app using Vaadin 8.6beta1. This app supports both Polling and Push. Not sure if you would ever mix both in a real web app, but perhaps.
Access the main files on my Google Drive. Add to a project created via the Maven archetype vaadin-archetype-application provided by Vaadin Ltd.
Caveat: This example was cobbled together part-time over days. So it may or may not be production-ready code, and may or may not show proper technique. But hopefully it will help to guide a newbie.
Caveat: I am not an expert in this arena. So take all my discussion above and my example code here with a grain-of-salt. Do your own research and study.
This app allows you to enable and disable each approach via radio buttons. You can also force an immediate refresh by clicking the Refresh manually now button.
The green-shading indicates changed values since the last refresh.
You can run multiple windows. Watch them update together or separately or not all, depending on your radio button settings.
Database
The main idea of this example app is to simulate a database maintaining a current status of some ten pieces of equipment/processes/people/whatever. Each status in identified by a number 1-10. Each has a status with a domain of ten values, 1-9. And each status records the moment it was last updated.
These ten status records are displayed as rows in a Vaadin Grid widget.
All this data is recorded in a relational database, the H2 Database Engine. As a demo, we’ve no need for persistence, so the database is in-memory. A background thread randomly updates the status rows in the database.
MyDbService.java
This database-service code establishes our in-memory H2 database, defining the table for our Status, and populating ten rows. This class also can randomly update the value of some of the rows. And you can ask to retrieve a List of Status objects representing the currently stored values.
Status.java
Each status record is represented in Java by the Status class, a simple POJO.
Lifecycle
Vaadin is based on Java Servlet technology. Your Vaadin app is one big Servlet implementation. As a servlet, it responds to incoming requests by the users’ web browsers.
Before that first incoming request, we need to do some set-up work. For one thing, we need to establish and populate that database with our ten status records.
The Servlet specification requires all web containers to support the ServletContextListener interface. If you write a class implementing that interface, and declare it to the web container, then it will be invoked before the first request and after the last request.
In our example, we use that hook to establish the database. We also set up a background thread that randomly changes our stored status records to simulate either users’ updates or fresh data from a feed.
Context listener
Here is our example ServletContextListener.
The easiest way to declare its presence to our web container is by the #WebListener annotation but you can choose other routes as needed in your deployment scenario.
#WebListener
public class MyServletContextListener implements ServletContextListener {
…
MyUI.java
The entry point into this Vaadin web app is our subclass of UI, MyUI.java. It has two jobs: (a) Get our user-interface content on-screen, and (b) Register itself as a PollListener to react to polling updates.
DataDisplayLayout.java
Here is our user-interface content. This is the centerpiece of this example app. It displays the Vaadin Grid whose display is to be updated with fresh data.
DataDisplayLayoutRefreshManager.java
This manager oversees the pub-sub (Publish-Subscribe) model of signing up instances of our DataDisplayLayout that want to be updated via Push.
A collection of weak references are used here to track the subscribers. So the subscribing DataDisplayLayout instance can gracefully notify of their desire to no longer be updated, or the instance can simply go out-of-scope to eventually be dropped as a subscriber.
The Polling approach does not need this manager, as each instance of our UI subclass (MyUI) is individually polling the server.
mytheme.scss
The green coloring of the cell in the Vaadin Grid denoting a fresh value is set via CSS. In Vaadin 8, we do this by editing the mytheme.scss file found buried in your project’s webapp folder.
Here we define the style name fresh_row.
#import "../valo/valo.scss";
#mixin mytheme {
#include valo;
// Insert your own theme rules here
.v-grid-row.fresh_row > td:nth-child(2) {
background-color: honeydew;
}
}
We must assign that style name to our Vaadin Grid rows by implementing a style generator.
this.grid.setStyleGenerator( ( StyleGenerator ) o -> {
Status s = ( Status ) o;
if ( s.getUpdated().isAfter( this.whenRowLastUpdated ) ) {
return "fresh_row";
} else {
return null;
}
} );

There are basically two ways of updating a Vaadin UI from background activity: poll and push. Each has their own pros and cons.
Polling is the technically more simple approach. It's based on a timer in the browser that triggers a request at a regular interval. Any pending changes will be delivered to the client in the response to that request. In addition, you can add a listener that gets run for every such request so that you can manually check for changes and if needed, update the UI.
Push is based on keeping a persistent connection open between the client and the server, so that the server can send changes to the client immediately instead of having to wait until the client opens a connection and asks for changes. The benefit here is that changes can be sent to the client immediately when they happen, instead of only at regular intervals.
Which to use depends on your requirements. Polling may use slightly less resources because there's no need to keep a connection open all the time. Polling may also be beneficial if there is no server-side trigger when the data changes, but instead, the server-side logic would still have to periodically explicitly check whether anything has changed. The main benefit of push is that changes can be sent immediately when something happens.

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

Creating thread for background task servlet

The scenario of my problem is:
In my servlet I get a large amount of data from somewhere (not relevant). I have to iterate over all this data and put it in an array, convert it to a JSON object and send it to the client side for viewing. If I do this in a single response it takes a very long time to display the results. Hence, I need to do multithreading.
The created thread needs to keep on adding data to the list while the main thread whenever it gets a request (requests for data keep on coming periodically) sends the present available list.
For instance on first request the response sent is : 1 2 3
Second request : 4 5 6 and so on.
Now I come to actual problem : I don't know how to do multithreading in a servlet. I have looked through numerous resources and examples but it only has confused me further. Some examples have created threads right in doGet which I think is very wrong, some have created them in the init() method but I dont know how can I pass parameters and get results from the thread if it is declared in the init method (It cannot be a global variable). Then there are examples of servletContextListener but I havent found anything useful or that makes sense.
Can anyone please guide to me a reliable source or just give me some sort of pseudo code to get a solution to my problem. It would be extremely helpful if the answers are in context with the aforementioned scenario.
Thanks

The created thread needs to keep on adding data to the list while the
main thread whenever it gets a request (requests for data keep on
coming periodically) sends the present available list.
If I got you correct, you like to get some data as background service and make them ready for clients once they request them(sounds like harvesting data).
Well, creating thread in web-apps, or generally stuffs come with managed environment is different, creating a thread implicitly would cause of memory leak.
One good solution would having a ThreadPool(either by container context/ndi or create it manually).
AND it MUST be created in a manageable manner, where you would control it by environment related events.
ContextListener is your friend, having a context listener class, like this.
public class dear_daemon implements ServletContextListener,Runnable{
ExecutorService the_pool;
Thread the_evil;
/*following get invoked once the context is called*/
public void contextInitialized(ServletContextEvent sce){
/*initialize the thread-pool, and run evil thread*/}
/*following get invoked once the context is destroying*/
public void contextDestroyed(ServletContextEvent sce){eviling=false;
/*stop evil(this) thread(first), then destroy thread pool*/
}
volatile boolean eviling=true;
public void run(){
while(eviling){
/*run Runnable instance which do data fetching using thread-pool*/
}
}
}
And register the listener in web.xml
<listener>
<listener-class>dudes.dear_daemon</listener-class>
</listener>
Having a class(runnable) which do the data fetching, and invoke it by evil thread, each instance using one thread.
The ContextLisstener helps you correctly shutdown and manage init and hult events by container, using the same thing with servlet init is possible, but make sure you do the same thing about hulting with destroy method of servlet.
If you like to do thread-thing about it, make sure you are doing things thread-safe since you have one thing to store data(a list).
If any synchronization is needed(for example ordering the fetched data), make sure you are doing it right, or you will face with deadlocks, or low-performance code.
If any(probably) IO action is needed for getting data, note java IO is blocking, so set appreciated read and connection timeouts, or switch to NIO if you can handle complex NIO stuffs.
If applying these changes make the environment complex, and you like to do alternative solutions, you may simply extract the data fetching from web-profile and run it as a external daemon-service or applciation, where the applciation will pass the fetched data to the server context using calling one of your CGI/Servlet.

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!