Question

I use vaadin + spring IOC + google guava eventbus. Resources recommends to use guava eventbus as singleton. But when I do that I have the following problem;

• Let’s say I run the application on 3 different browsers at the same time, so I have 3 different instances of my application.

• then for example when an I press a button on one browser and fire an event, I notice that my related listener method with the @subscribe annotation gets called 3 times!

Is this is a normal behaviour I would expect because I use eventbus as singleton? If not what is going on here? MainController is a spring managed bean with a a custom Vaadin Application Scope

class MainController{
  public MainController() throws DAOException, Exception {
    EventBusFactory.getEventBusInstance().register(this);
  }

  @Subscribe
  public void addFacetEvent(FacetAddedEvent event) throws DAOException {
    getTreeTableView().addToList(event.getData());
  }
} 

class EventBusFactory{
  public static EventBus getEventBusInstance() {
        if(eventBus==null){
            eventBus=new EventBus();
        }
        return eventBus;
    }
}

P.s I also hesitate in Vaadin should I to use guava eventbus or guava gwt event bus?

Thanks

Answer 1

Short answer: It’s normal and expected behaviour in this configuration (you have three Vaadin Applications and hence three MainController instances managed with single EventBus).

---

By custom Vaadin Application Scope did you mean scope from this Vaadin addon?

Anyway, it’s simple to reproduce your situation having prototype-scoped MainController bean and Vaadin App like this:

public class SandpitApplication extends Application {
  private static final long serialVersionUID = 1L;
  private static final Logger log = Logger.getLogger(SandpitApplication.class);

  // https://vaadin.com/wiki/-/wiki/Main/Spring%20Integration#section-Spring+Integration-SpringContextHelperClass
  private SpringContextHelper ctx;

  @Override
  public void init() {
    // vaadin stuff
    setTheme("common");
    final Window mainWindow = new Window("Vaadin Sample Application");
    setMainWindow(mainWindow);

    // get your bean from spring
    log.info("start SandpitApplication@" + Integer.toHexString(hashCode()));
    ctx = new SpringContextHelper(this);
    // create application-wide bean
    final MainController mainController = ctx.getBean("mainController");

    mainWindow.addComponent(new Button("click to post", new Button.ClickListener() {
      @Override public void buttonClick(final ClickEvent event) {
        log.info("click on button");
        EventBusFactory.getEventBusInstance().post(
            new FacetAddedEventImpl("click-"
                + new SimpleDateFormat("HH:mm:ss").format(new Date())));
        log.info(mainController);
      }
    }));
  }
}

and MainController class:

class MainController {
  private static final Logger log = Logger.getLogger(MainController.class);

  public MainController() {
    log.info("creating MainController@" + Integer.toHexString(hashCode()));
    EventBusFactory.getEventBusInstance().register(this);
  }

  @Subscribe
  public void addFacetEvent(final FacetAddedEvent event) {
    final String signature = "MC@" + Integer.toHexString(hashCode()) + ": ";
    log.info("addFacetEvent in " + signature + event);
    // getTreeTableViewBuilder returns extended ArrayList with fancy add
    getTreeTableViewBuilder().addFacetToList(signature + event.getData());
  }

  // plus other stuff like toString etc.
}

When you do the following:

1. Start the vaadin app in your browser (App#1).
2. Click the App1#button.
3. Start another app (App#2).
4. Click the App2#button
5. Go back to tab with App#1.
6. Click the App1#button.

you’ll get the following output:

start SandpitApplication@75a5555a
creating MainController@2e98f864
click on button // #1
addFacetEvent in MC@2e98f864: FacetAddedEventImpl@6b527dc6{data: click-13:42:45}
MainController@2e98f864{treeTableViewBuilder: [MC@2e98f864: click-13:42:45]}
start SandpitApplication@3f9e529
creating MainController@2f8d604f
click on button // #2
addFacetEvent in MC@2e98f864: FacetAddedEventImpl@36c1fc67{data: click-13:42:47}
addFacetEvent in MC@2f8d604f: FacetAddedEventImpl@36c1fc67{data: click-13:42:47}
MainController@2f8d604f{treeTableViewBuilder: [MC@2f8d604f: click-13:42:47]}
click on button // #1
addFacetEvent in MC@2e98f864: FacetAddedEventImpl@42d32028{data: click-13:42:49}
addFacetEvent in MC@2f8d604f: FacetAddedEventImpl@42d32028{data: click-13:42:49}
MainController@2e98f864{treeTableViewBuilder: [MC@2e98f864: click-13:42:45, MC@2e98f864: click-13:42:47, MC@2e98f864: click-13:42:49]}

You should now see that singleton EventBus is managing two application-wide MainController beans and each is recieving event (because it’s resolved by global EventBus).

Trying to guess what do you want to achieve, I’d say that you need create application-wide event bus bean:

<bean id="eventBus" class="com.google.common.eventbus.EventBus"
    scope="vaadinApplication" />

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About P.S.: We use standard Guava in our Vaadin project extensively, no need for GWT version.