Vaadin “A connector with id xy is already registered”

Question

Somewhere in my Vaadin application, I\'m getting this exception as soon as I connect using a second browser

Caused by: java.lang.RuntimeException: A connector

Answer 1

Yes, this usually happens because you are attaching a component already attached in other session.

Try logging the failed connector with a temporal ConnectorTracker, So the next time that it happens, you can catch it.

For example:

public class SomeUI extends UI {

  private ConnectorTracker tracker;

  @Override
  public ConnectorTracker getConnectorTracker() {
    if (this.tracker == null) {
      this.tracker =  new ConnectorTracker(this) {

        @Override
        public void registerConnector(ClientConnector connector) {
          try {
            super.registerConnector(connector);
          } catch (RuntimeException e) {
            getLogger().log(Level.SEVERE, "Failed connector: {0}", connector.getClass().getSimpleName());
            throw e;
          }
        }

      };
    }

    return tracker;
  }
}

Answer 2

Here is how I fixed it -

1) look for components you have shared across sessions. For example if you have declared a component as static it will be created once and will be shared.

2) if you are not able to find it and want a work around until you figure out the real problem, put your all addComponent calls in try and in catch add following code -

getUI().getConnectorTracker().markAllConnectorsDirty();
getUI().getConnectorTracker().markAllClientSidesUnititialized();
getPage().reload():

This will clear old connectors and will reload the page properly only when it fails. For me it was failing when I was logged out and logged in back.

Once you find the real problem you can fix it till then inform your customers about the reload.

**** note - only solution is to remove shared components this is just a work around.

Answer 3

By running your application in debug mode (add ?debug at the end of URL in browser) you will be able to browse to the component, e.g:

-UIConnector(0)
--VerticalLayoutConnector(1)
---...
---LabelConnector(22)

where 22 is id from your stack trace. Find this component in your code and make sure that it is not static (yes, I saw such examples).

Answer 4

I think I might be stealing UI components from the other session - which is not my intention. Currently, I don't see any static instances of UI components I might be using in multiple sessions.

That was it. I was actually stealing UI components without prior knowledge.

It was very well hidden in a part which seems to be same for all instances. Which is true: the algorithm is the same.

Doesn't mean I should've reused the same UI components as well...

Thanks to those who took a closer look.