Java 8 Optionals, Combining Statements

Question

I'm new to Java 8 optionals and I'm wondering if there is a way to combine these two statements into one while retaining the optional?

public List<String> getEmployeeStreetNames(Employee employee){
     List<Addresses> addresses = Optional.ofNullable(employee)
     .map(Employee::getAddresses)
      .orElse(new ArrayList<>());

   return addresses.stream()
       .map(Address::getStreetName)
       .collect(Collectors.toList())
}

Any help is greatly appreciated.

Answer 1

First, avoid creating new objects in "maybe" pipeline steps like orElse; you always incur the overhead of creating the parameter even if it's unused. Prefer signatures like Supplier<T> or, in this case, Collections.emptyList(). (This is especially important for exceptions; always use MyException::new or () -> new MyException(foo).)

In this case there are a couple of ways to handle the pipeline, either nested or consecutive.

return Optional.ofNullable(employee)
    .map(Employee::getAddresses)
    .map(a -> a.stream().map(Address::getStreetName).collect(toList()))
    .orElse(emptyList());

return Optional.ofNullable(employee)
    .map(Employee::getAddresses)
    .orElse(emptyList())
    .stream()
    .map(Address::getStreetName)
    .collect(toList());

I'd generally go with the nested version, since the nested pipeline isn't at all difficult to understand.