Checking for "nested" null attributes in Java

Question

I've got a simple method that checks there are no null in attributes:

public boolean isValid(){
     return session.getX() != null && session.getX().getY() != null &&
     session.getX().getY().getZ() != null;
}

This works, but, Is there any way to do this in a more elegant way?

Thanks a lot in advance.

[Avoiding != null statements](http://stackoverflow.com/questions/271526/avoiding-null-statements) — Landaida, Jan 13 '17 at 11:37
it looks like codesmell and violation of https://en.wikipedia.org/wiki/Law_of_Demeter — Vlad Bochenin, Jan 13 '17 at 11:44
Possible duplicate of [Check chains of "get" calls for null](http://stackoverflow.com/questions/3458451/check-chains-of-get-calls-for-null) — Tom, Jan 13 '17 at 12:00
With a field, the responsibility of not letting it be null follows. — Anders Lindén, May 04 '17 at 07:58

davidxxx · Answer 1 · 2017-01-13T11:35:39.377

1

This works, but, Is there any way to do this in a more elegant way?

With a utility class which performs reflection to retrieve the nested fields and do the check, it may be more elegant but it is surely less safe and slower:

public boolean isValid(){
     return NullAnalyser.isNotNull(session, "x.y.z");
}

Another idea would be to return a special type that allows to avoid NPE in the getter. But it makes them more complex. Is it desirable ?

edited Jan 13 '17 at 11:35

answered Jan 13 '17 at 11:31

davidxxx

125,838
23
214
215

Thanks for your answer @davidxxx. I was thinking in reflection as well, but I'd like to get an existing library, if possible, in order to avoid "reinventing the wheel" – stack man Jan 13 '17 at 11:35
You are welcome. BeanUtils should do the job. For example `BeanUtils.getProperty(session, "x.y.z");` https://commons.apache.org/proper/commons-beanutils/apidocs/org/apache/commons/beanutils/BeanUtils.html – davidxxx Jan 13 '17 at 11:44

score 1 · Answer 2 · answered Jan 13 '17 at 11:47

This way is elegant if you are using java 8:

public boolean isValid(){
     return Optional.of(session)
                    .map(x -> x.getX())
                    .map(x -> x.getY())
                    .map(x -> x.getZ())
                    .isPresent());
}

Conor Restall · Answer 3 · 2017-01-13T19:37:39.150

0

Similarly to what Dimitry said if you are using Java 8 and have control over Session, X, Y and Z then you can change the signatures to return Optionals.

You can also use method references instead of lambdas which are arguably easier to read.

public boolean isValid(){
     return Optional.of(session)
                    .map(Session::getX)
                    .map(X::getY)
                    .map(Y::getZ)
                    .isPresent());
}

edited Jan 13 '17 at 19:37

answered Jan 13 '17 at 11:58

Conor Restall

33
8

Yes, references are good but we don't know actual class names from the question, moreover you should remove "()" in all maps to avoid compile error. – Dmitry Gorkovets Jan 13 '17 at 12:04

Checking for "nested" null attributes in Java

3 Answers3