Ok, this is actually a comment I made.
Bpbasilphx is correct that, in a certain sense, we are to be happy in this world. And I think joy is that sense. Because happiness is our ultimate goal in all that we do, and this happiness only comes from union with God (in fact, some, myself included, would say that the search for happiness is the search for God) true happiness is only found in Heaven. We speak of happiness in this world, but we mean many different things. We might mean pleasure, we might mean freedom from suffering, we might mean contentment. Happiness includes all these things, but true happiness is eternal rather than temporal.
One difference between happiness and joy is that happiness precludes all suffering. There cannot be happiness when there is suffering. Joy, however, exists despite suffering because it flows from love. That is how it is a gift from the Holy Spirit, which is the bond of love between the Father and the Son. So we can feel joy in our hope of happiness, we can feel joy at the sight of our Redeemer, despite our sins and despite our sufferings.
As for the context of this statement, a friend asked me asked me why I am not happy (in response to a comment I made), and this was my response (though I forgot to mention that I do have joy!)
As for what St. John Bosco said, I haven’t read anything he’s written, but I suspect I wouldn’t disagree with him. If he did use the word “happy”, he probably means it in a less restricted sense than I am using it.