We Keep Coding

GWT Updating Main Content using EventBus and ActivityMapper - Can GWT help me to do this cleaner?

I would like to know
Am I doing things (the following) too complicated?
Is there a better way to update the main content of an activity that allows me to bookmark the event calendar of a store via URL like #MainPlace:eventCalendar?storeId=<id>?
I'm having this ActivityMapper here
public class AppActivityMapper implements ActivityMapper {
private ClientFactory clientFactory;
private MainActivity mainActivity;
// ..
#Override
public Activity getActivity(Place place) {
if (place instanceof LoginPlace) {
return new LoginActivity((LoginPlace) place, clientFactory);
} else if (place instanceof MainPlace) {
if(this.mainActivity == null) {
this.mainActivity = new MainActivity((MainPlace) place, clientFactory);
} else {
this.mainActivity.updateMainContent(((MainPlace) place).getMainContentToken());
}
return this.mainActivity;
}
return null;
}
}
and a MainActivity that controls my MainView that is just a menu ond the left side and the main content on the right side.
I want to decouple my views like in Best Practices for Architecting GWT App which is why I'm trying to control the main content by using events that get fired as something gets clicked in my MenuView.
Therefore I am initializing some event handlers in my MainActivity that react to clicks on the buttons in my menu to delegate the update to the MainView.
public class MainActivity extends AbstractActivity implements MainView.MainPresenter {
#Override
public void start(AcceptsOneWidget panel, EventBus eventBus) {
this.mainView = this.clientFactory.getMainView();
this.mainView.setPresenter(this);
this.mainView.initialize();
this.eventBus = eventBus;
this.eventBus.addHandler(HomeClickedEvent.TYPE, new HomeClickedHandler() {
#Override
public void onHomeClicked(HomeClickedEvent event) {
goTo(new MainPlace("home"));
}
});
this.eventBus.addHandler(EventCalendarClickedEvent.TYPE, new EventCalendarClickedHandler() {
#Override
public void onEventCalendarClicked(EventCalendarClickedEvent eventCalendarClickedEvent) {
goTo(new MainPlace("eventCalendar?storeId=" + eventCalendarClickedEvent.getStoreId()));
}
});
panel.setWidget(this.mainView.asWidget());
}
#Override
public void goTo(Place place) {
this.clientFactory.getPlaceController().goTo(place);
}
#Override
public void updateMainContent(String currentMainContentToken) {
this.mainView.updateMainContent(currentMainContentToken);
}
}
this event gets fired by MenuPresenter.clickedEventCalendar() that reacts to a click on the corresponding menu entry of the MenuView:
public class MenuPresenter implements MenuView.MenuPresenter {
// ..
#Override
public void clickedEventCalendar(Long storeId) {
this.eventBus.fireEvent(new EventCalendarClickedEvent(storeId));
}
}
One of the things I really don't like is this where I append parameters to the token e.g. to display the event calendar of a store given by storeId:
#Override
public void onEventCalendarClicked(EventCalendarClickedEvent eventCalendarClickedEvent) {
goTo(new MainPlace("eventCalendar?storeId=" + eventCalendarClickedEvent.getStoreId()));
}
is there a cleaner solution for a problem like this in GWT? I don't like the fact that I'd have to parse that string in my actual event calendar. Am I using the ActivityMapper wrong or is there simply no other way to do this?

This question should really be split into several separate ones, but that's maybe something to keep in mind for the future. If you're asking one thing then it's easier to answer thoroughly and others can find the answer easier too.
Anyway, I can see a few improvements:
use EventBinder to get rid a bit of the cruft when handling and creating new events.
if you just want to let the presenter know that a button was pressed on in the view (associated with that presenter) sending a custom event over the event bus is a bit of an overkill. Depending on your needs you can expose the button in your view's interface:
public interface Display {
HasClickHandlers getButton();
}
And then just register the ClickHandler in your presenter.
Or, if you need to do something view- and presenter- related on the click, register the ClickHandler in your view and call the presenter:
// In MainView:
#UiHandler("button")
void handleClick(ClickEvent event) {
// Do some stuff with view,
// like hide a panel or change colour
panel.setVisible(false);
// Let the presenter know that a click event has been fired
presenter.onEventCalendarClicked();
}
you're right - creating MainPlace like you are proposing is wrong. You are creating the token too soon - that's what the tokenizer associated with the place is for. You should create MainPlace by passing just the storeId to the constructor - why should MainPresenter (or any other class using this place) should know how to create the token? MainPlace should look more like this:
public class MainPlace extends Place {
private final Long storeId;
public MainPlace(Long storeId) {
this.storeId = storeId;
}
public Long getStoreId() {
return storeId;
}
public static class Tokenizer implements PlaceTokenizer<MainPlace> {
#Override
public MainPlace getPlace(String token) {
return new MainPlace(Long.valueOf(token));
}
#Override
public String getToken(MainPlace place) {
return "eventCalendar?storeId=" + place.getStoreId();
}
}
}
Now, it's the Tokenizer's responisibily to create and parse the token. Just remember to register it on your PlaceHistoryMapper.

JavaFX events/listeners/handlers

I have 2 listViews and 2 custom controls on my scene. When i press on an item in the listView, i would like to raise the event, and then be able to handle this anywhere else in the application. Ideally i would like my 2 custom controls to listen for this event, and handle it when it is raised.
Not sure if this is right, but so far i have this
Here is my custom event, i would also like to pass in an argument of which Offer is it, not sure how to do this though?
public class OfferChangedEvent extends Event {
private static final long serialVersionUID = 1L;
public static final EventType<OfferChangedEvent> OFFER_CHANGED = new EventType<OfferChangedEvent>(ANY, "OFFER_CHANGED");
public OfferChangedEvent() {
this(OFFER_CHANGED);
}
public OfferChangedEvent(EventType<? extends Event> arg0) {
super(arg0);
}
public OfferChangedEvent(Object arg0, EventTarget arg1, EventType<? extends Event> arg2) {
super(arg0, arg1, arg2);
}
}
Now on one of my custom controls, i raise the event when a button is clicked, like so
#FXML
public void showOffer(ActionEvent event) {
Button btnView = (Button)event.getSource();
// can i pass in parameter of the offer here??
btnView.fireEvent(new OfferChangedEvent());
}
Now i would like a listview to listen for the event and handle it, i have this but it aint working
// when offer is changed, we dont want to see events
this.eventListPane.addEventHandler(OfferChangedEvent.OFFER_CHANGED, new EventHandler<OfferChangedEvent>() {
#Override
public void handle(OfferChangedEvent event) {
Console.Log("Recived");
eventListPane.setVisible(false);
// How can i get the argument of the offer passed???
}
});

Unfortunately there isn't a straightforward answer to this question. For your case there are about 3 different ways to wire up your application so that different parts can react to changes in other parts:
You could bind to properties and listen for changes.
You could setup listeners and then notify them of changes.
You could use a messaging bus.
Which one you use depends on various factors, but considering what you have done above I would go with number three. You can try this https://github.com/bennidi/mbassador

Testing Presenters in MVP GWT application

I have a simple application and want to make it testable. I m new in this area.
Here is a simple Presenter, taking in mind this code ,could you advice or give me some example how to test it.
public class SomePresenter extends Presenter<MainPanelPresenter.Display>
{
public interface Display extends WidgetDisplay
{
HasClickHandlers getAddButton();
HasClickHandlers getDeleteButton();
void setData(ArrayList<Person> data);
ArrayList<String> getSelectedRows();
Widget asWidget();
}
private final DispatchAsync dispatcher;
public static final Place PLACE = new Place("main");
#Inject
public SomePresenter(DispatchAsync dispatcher, EventBus eventBus, Display display)
{
super(display, eventBus);
this.dispatcher = dispatcher;
bind();
}
protected void onBind()
{
display.getAddButton().addClickHandler(new ClickHandler()
{
public void onClick(ClickEvent event)
{
eventBus.fireEvent(new AddButtonEvent());
}
});
display.getDeleteButton().addClickHandler(new ClickHandler()
{
public void onClick(ClickEvent event)
{
ArrayList<String> list = display.getSelectedRows();
deletePerson(list);
}
});
}
....
private void loadDbData()
{
..........
}
private void deletePerson(ArrayList<String> ids)
{
..........
}
}
Edit:
What does the Presenter is, load initial data from db, have 2 buttons add and delete.
When add is press then a new form is load and user is able to input data and save to the db,
delete button just delete person from db.
Thanks

The general idea of unit testing such a class would be, like for any other class :
create Mock version of the dependencies (Display, EventBus, etc...)
set expectations on what the depdencies should do when the Presenter works
exercice the Presenter and check the expectations
However there are a couple of issues with your version of the Presenter :
The loadDbData() method is not showed, but I assumed it means the Presenter also has access to some other component that does the fetching. Can this component be abtracted in a dependency, and mocked liked the rest ?
Then there is the testing of bind(). The only responsibility of your Presenter in this method is to set up callbacks on some buttons provided by the Display. What you want to test is both :
That the callbacks are set
That the set callbacks do the expected things
A few ideas to help with the later :
You can reduce the coupling between Presenter and Button. If possible, change the Display interface from :
Button getAddButton();
to
addAddButtonClickedHandler(ClickHandler);
This means your Presenter does not have to use a Display object that returns actual BUtton
You can reduce the callbacks content to calling a single method, that you can then test in isolation
protected void bind() {
display.addAddButtonClickHandler(new ClickHandler() {
public void onClick(ClickEvent) {
fireAdded();
}
});
}
// The fireAdded function can be tested independenty of the Display, potentially with
// a mock EventBus
protected void fireAdded() {
event.fireEvent(....)
}
If you really want to check that the callbacks are properly set, than you can use a 'Dummy' implementation of the Display class, that provides you a list of all the callbacks, and let you call them
private class DummyDisplay implements Display {
private List<ClickHandler> addButtonClickHandlers;
public void addAddButtonClickHandler(ClickHandler handler) {
addButtonClickHandlers.add(handler);
}
public void fireAddButtonClick() {
for (ClickHandler h in addButtonClickHandlers) {
h.onClick(new ClickEvent());
}
}
// ....
}
Then your test would :
create a presenter with such a dummy display
use bind to set the callbacks
use display.fireAddButtonClick() to simulate a user clicking
check that has the result of the click, the effects of fireAdded are seen
This type of class (that mostly glue other classes together) can tend to be hard to test ; at some point, it the other classes are thoroughly tested it can become slightly counter productive to concentrate on the gluers, rather than the glued.
Hoping this helps.

Passing Swing classes (references) on network?

I want to know that is it possible to send major Swing classes event/actionlisteners, Events, components via RMI.
Possible scenario: If one client press the button or move the slider every client's button or slider move etc same for other swing elements.
I am expecting the answer in the context of RMI and swing MVC architecture, i want to call the swing component's models e.g ButtonModel and want to send swing ActionEvent on wire and register PropertyChangeListener/PropertyChangeSupport as remote objects for getting updates at client site.
typical examples :
the server should call this method for each client, when ever some change occur in model
public void propertyChange(PropertyChangeEvent evt) {
for (AbstractViewPanel view: registeredViews) {
view.modelPropertyChange(evt);
}
}
in case of an event on one client, each client actionPerformed should be called from server:
#Override
public void actionPerformed(ActionEvent e) {
}
is it feasible? if not then why? where i could face the problems, i mean which classes are transferable (serialized) and which are not...
EDIT: here you see i m invoking Java Swing defaultbuttonmodel remotely, the only thing left when some of it's property or method change the other client's get updates, best would be following swing propertychangelistener if someone can just help me, realizing this, it would be great:
public class RemoteButtonModel extends UnicastRemoteObject implements Model {
private ButtonModel model = new DefaultButtonModel() ;
protected myModel() throws RemoteException {
super();
}
#Override
public void setEnabled(boolean b) throws RemoteException {
if (isEnabled())
model.setEnabled(false);
else{
model.setEnabled(true);
}
}
#Override
public boolean isEnabled() throws RemoteException {
return model.isEnabled();
}
}

I think it would be more efficient to send across something like a "scroll message" or "button pressed" message, utilizing the command pattern. This would allow different clients to act correctly with different implementations.
Edits:
the way I do it in my client/server applications (which is easily adapted to this peer-to-peer architecture you're doing) is with something like this (copy and pasted from my production code, mind you.)
abstract public class UserRequest implements Serializable {
public final String username;
private transient ServersideThread thread;
protected UserRequest(String username) {
this.username = username;
this.thread = null;
}
abstract public EngineMessage engineCallback(GenericEngine engine);
public void setThread(ServersideThread thread) {
if(this.thread == null) {
this.thread = thread;
return;
}
throw new IllegalStateException("Cannot set thread when already set:" + thread.getName());
}
public ServersideThread getThread() {
return this.thread;
}
}
So, with this approach, I would do something like...
public class SliderMoveNotification extends UserRequest {
// need some way to say what slider moved
public final int sliderId;
public final int slideDistance;
public SliderMoveNotification(String username) {
super(username);
sliderId = 0;
sliderDistance = 0;
throw new UnsupportedOperationException("Must supply a slider and a distance");
}
public SliderMoveNotification(String username, int sliderID, int slideDistance) {
super(username);
this.sliderId = sliderId;
this.slideDistance = slideDistance;
}
public EngineMessage engineCallback(GenericEngine engine) {
if(engine instanceof WindowEngine) {
WindowEngine manager = (WindowEngine)engine;
manager.slideWindow(sliderId,slideDistance);
// you wouldn't need engine messages like I do in my client/server
// relationship, but the idea stands.
}
}
}

The Javadoc for every Swing class says that it should not be serialized.
More probably you should be transmitting the associated Model classes.
And event listening via RMI is an anti-pattern. Too much traffic, too many points of failure.

Generic, annotation-driven event notification frameworks

While simple, interface-driven event notification frameworks in Java have been around since pre-Cambrian times (e.g. java.beans.PropertyChangeSupport), it is becoming increasingly popular for frameworks to use annotation-driven event notification instead.
For an example, see JBossCache 2.2. The listener class has its listener methods annotated, rather than conforming to a rigid interface. This is rather easier to program to, and easier to read, since you don't have to write empty implementations of listener callbacks that you're not interested in (and yes, I know about listener adapter superclasses).
Here's a sample from the JBossCache docs:
#CacheListener
public class MyListener {
#CacheStarted
#CacheStopped
public void cacheStartStopEvent(Event e) {
switch (e.getType()) {
case Event.Type.CACHE_STARTED:
System.out.println("Cache has started");
break;
case Event.Type.CACHE_STOPPED:
System.out.println("Cache has stopped");
break;
}
}
#NodeCreated
#NodeRemoved
#NodeVisited
#NodeModified
#NodeMoved
public void logNodeEvent(NodeEvent ne) {
log("An event on node " + ne.getFqn() + " has occured");
}
}
The problem with this, is that it's very much more of an involved process writing the framework to support this sort of thing, due to the annotation-reflection nature of it.
So, before I charge off down the road of writing a generic framework, I was hoping someone had done it already. Has anyone come across such a thing?

You can already do this today with EventBus.
Following example is from EventBus Getting Started guide. Statusbar that updates based on published events, and no need to register statusbar control/widget as listener of publisher(s). Without EventBus, statusbar will need to be added as listener to many classes. Statusbar can also be created and destroyed at any time.
public StatusBar extends JLabel {
public StatusBar() {
AnnotationProcessor.process(this);
}
#EventSubscriber(eventClass=StatusEvent.class)
public void updateStatus(StatusEvent statusEvent) {
this.setText(statusEvent.getStatusText();
}
}
A similar project is ELF (Event Listener Framework) but it seems to be less mature.
I'm currently researching about event notification frameworks on Publish-Subscribe Event Driven Programming | Kev's Spring vs Java EE Dev and the followup articles.

I've made http://neoevents.googlecode.com to handle this kind of annotation based event handler.
#actionPerformed
private void onClick() {
//do something
}
protected void initComponents() {
JButton button = new JButton("Click me!!!");
button.addActionListener(new ActionListener(this) );
}
It looks as simple as I was expecting it to be. Annotations are available for every single listener in J2SE.

Don't mistake complicated for clever. It seems to me that this would be:
A nightmare to debug
Difficult to follow (from a maintenance perspective, or someone attempting to change something 6 months down the line)
Full of if (event instanceof NodeCreatedEvent) like code. Why this is better than subclassing an adapter I have no idea!

The main problem I see here are the method parameters, which restrict which methods can actually be used for which events, and there's no compile-time help for that.
This is what makes interfaces attractive to me for observer pattern implementations like the Java event model. Tools like eclipse can autogen method stubs so you can't get the signatures wrong. In your example, it's very easy to use the wrong parameter type and never know it until an event occurs (which might be an error case several months down the line)
One thing you might try are my annotations & processor for implementing observers and null object implementations. Suppose you have
package a.b.c;
public interface SomeListener {
void fee();
void fie();
void fo();
void fum();
}
and wanted to create a listener instance. You could write
package x.y.z;
import a.b.c.SomeListener;
import com.javadude.annotation.Bean;
import com.javadude.annotation.NullObject;
#Bean(nullObjectImplementations = {#NullObject(type = SomeListener.class) })
public class Foo extends FooGen implements SomeListener {
#Override
public void fie() {
// whatever code you need here
}
}
To create a source for these events, you can write
package a.b.c;
import com.javadude.annotation.Bean;
import com.javadude.annotation.Observer;
#Bean(observers = {#Observer(type = SomeListener.class)})
public class Source extends SourceGen {
// SourceGen will have add/remove listener and fire methods
// for each method in SomeListener
}
See http://code.google.com/p/javadude/wiki/Annotations if you're interested. Might give you some other ideas as well.

Google Guava v11 has added an EventBus component that uses this style. They also explain why they decided to use annotations rather than interfaces.

I've been thinking about a generic annotation-driven event framework as well. I like the benefits provided by static typing, but the current interface-driven event model is painful to use (ugly code). Would it be possible to use a custom annotation processor to do some compile-time checking? That might help add some of the missing "safety" that we've all grown used to.
A lot of the error checking can also be done at the time that the listeners are "registered" with the event producers. Thus, the application would fail early (when the listeners are registered), possibly even at at startup-time.
Here's an example of what the generic framework I've been toying with might look like:
public class ExampleProducer {
private EventSupport<ActionEvent> eventSupport;
public ExampleProducer() {
eventSupport = new EventSupport<ActionEvent>(this);
}
#AddListenersFor(ActionEvent.class)
public void addActionListener(Object listener)
{
eventSupport.addListener(listener);
}
#RemoveListenersFor(ActionEvent.class)
public void removeActionListener(Object listener)
{
eventSupport.removeListener(listener);
}
public void buttonClicked() {
eventSupport.fire(new ActionEvent(this,
ActionEvent.ACTION_PERFORMED, "Click"));
}
}
The producer uses EventSupport, which uses reflection to invoke the events. As mentioned before, EventSupport could preform some initial checks when the events listeners are registered.
public class ExampleListener
{
private ExampleProducer submitButton;
public ExampleListener()
{
submitButton = new ExampleProducer();
EventSupport.autoRegisterEvents(this);
}
#HandlesEventFor("submitButton")
public void handleSubmitButtonClick(ActionEvent event)
{
//...some code to handle the event here
}
}
Here, EventSupport has a static method that uses reflection to auto-register the listener with the event producer. This eliminates the need to manually register with the event source. A custom annotation processor could be used to validate that the #HandlesEventFor annotation refers to an actual field of the ExampleListener. The annotation processor could do other checks as well, such as ensuring that the event handler method signature matches up with one of the registration methods on the ExampleProducer (basically, the same check that could be performed at registration-time).
What do you think? Is this worth putting some time into fully developing?

Here's a similar project called SJES.
public class SomeController {
private Calculator c1 = new Calculator();
private Calculator c2 = new Calculator();
public SomeController() {
c1.registerReceiver(this);
c2.registerReceiver(this);
c1.add(10, 10);
c2.add(20, 20);
}
#EventReceiver(handleFor="c1")
public void onResultC1(Calculator.Event e) {
System.out.println("Calculator 1 got: " + e.result);
}
#EventReceiver(handleFor="c2")
public void onResultC2(Calculator.Event e) {
System.out.println("Calculator 2 got: " + e.result);
}
#EventReceiver
public void onResultAll(Calculator.Event e) {
System.out.println("Calculator got: " + e.result);
}
}
public class Calculator {
private EventHelper eventHelper = new EventHelper(this);
public class Event {
long result;
public Event(long result) {
this.result = result;
}
}
public class AddEvent extends Event {
public AddEvent(long result) {
super(result);
}
}
public class SubEvent extends Event {
public SubEvent(long result) {
super(result);
}
}
public void unregisterReceiver(Object o) {
eventHelper.unregisterReceiver(o);
}
public void registerReceiver(Object o) {
eventHelper.registerReceiver(o);
}
public void add(long a, long b) {
eventHelper.fireEvent(new AddEvent(a + b));
}
public void sub(long a, long b) {
eventHelper.fireEvent(new SubEvent(a - b));
}
public void pass(long a) {
eventHelper.fireEvent(new Event(a));
}
}
I think this is very easy to use.

You can also check out MBassador It is annotation driven, very light-weight and uses weak references (thus easy to integrate in environments where objects lifecycle management is done by a framework like spring or guice or somethign).
It provides an object filtering mechanism (thus you could subscribe to NodeEvent and attach some filters to restrict message handling to a set of specific types only).
You can also define your own annotations to have customized declaration of your handlers.
And it's very fast and resource efficient. Check out this benchmark showing a performance graph for different scenarios using Guava or mbassador.