Java Stream API how to improve expression

Question

I have the following code:

public List<Entry> getEntriesForUserId(int userId) {
    User u = DataBaseConnector
        .getAllUsers()
        .stream()
        .filter(user -> user.getUserId() == userId)
        .findFirst()
        .orElse(new User(-1, "Error");
    return u.getEntries();
}

getEntries() returns a List<Entry>.

How can I add the return statement into this lambda expression? Something like .map(User::getEntries)?

Answer 1

You don't need lambda to return the list, you can just say:

public List<Entry> getEntriesForUserId(int userId) {
    return DataBaseConnector
             .getAllUsers()
             .stream()
             .filter(user -> user.getUserId() == userId)
             .findFirst()
             .orElse(new User(-1, "Error")
             .getEntries();
}

Answer 2

The answer is here already, but let me add one more thing - remember to use orElseGet instead of orElse in such cases. It will not create User eagerly:

.orElseGet(() -> new User(-1, "Error")

Answer 3

Since the entire Stream method chain returns a single User u and then you call return u.getEntries();, feel free to append the second line to the end of Stream and return it as is:

return DataBaseConnector.getAllUsers().stream()
                                      .filter(user -> user.getUserId() == userId)
                                      .findFirst()
                                      .orElse(new User(-1, "Error"))
                                      .getEntries();