After going though the JCA specs I could make that there is one-one relationship between ConnectionEventListener AND ManagedConnection.
In the BaseWrapperManagedConnection I can see

private final Collection cels = new ArrayList();

The closeHandle(Object) in the BaseWrapperManagedConnection has

synchronized(cels)
 {
 copy = new ArrayList(cels);
 }
 for (Iterator i = copy.iterator(); i.hasNext(); )
 {
 ConnectionEventListener cel = (ConnectionEventListener)i.next();
 cel.connectionClosed(ce);
 }

which could have been replaced by

cel.connectionClosed(ce)

if we have this

private final Collection cels = new ArrayList();

replaced by

private ConnectionEventListener cel ;

I am not able to understand why we have ConnectionEventListener associated with ManagedConnection stored as ArrayList as I expect this ArrayList will always have single CEL.