Tyulpan Tyulpan :
What I'm trying to do is to filter the list, then map it and use orElse if null and then collect it back to the list. Now I can achieve it this way:
return users.stream()
.filter(user -> id.equals(user.getId()))
.map(
user -> {
if(user.getData() != null) {
return user.getData();
}
return Collections.emptyMap();
}
)
.collect(Collectors.toList());
But the question is: how can I make this structure better and why cannot I use orElse in this case?
Eran :
It might be more readable with ternary conditional operator:
return users.stream()
.filter(user -> id.equals(user.getId()))
.map(
user -> (user.getData() != null)
? user.getData()
: emptyMap()
)
.collect(Collectors.toList())
;
In order to use orElse you'll have to create an Optional that wraps user.getData(). I'm not sure that's a good idea.
If you insist on using orElse (or even better, orElseGet, to avoid evaluating emptyMap() when it's not required), it can look like this:
return users.stream()
.filter(user -> id.equals(user.getId()))
.map(
user -> Optional.ofNullable(
user.getData()
).orElseGet(
() -> emptyMap()
)
)
.collect(Collectors.toList())
;