Java Streams - check if list is null

Question

I wonder what's teh best approach to check if list is null. In my Stream I call orElseThrow twice. It works but I don;t know if its correct? It looks a little bit ugly:

Optional.ofNullable(listCanBeNull)
                .orElseThrow(() -> new ResourceNotFoundException("the same error message"))
                .stream()
                .filter(configuration -> configuration.getId().equals(warehouseConfigurationId))
                .findAny()
                .orElseThrow(() -> new ResourceNotFoundException("the same error message"));

I have to throw error when list is null and when no item was found

The Java stream interface is convenient, but it doesn't have to consume your entire program. Sometimes the most readable thing is a good old-fashioned if (list == null) { throw blah; } at the start of your loop. — Silvio Mayolo
– Silvio Mayolo, Commented Aug 18, 2022 at 15:34
And for starters, a List shouldn't be null, it should be empty instead. — MC Emperor
– MC Emperor, Commented Aug 18, 2022 at 15:40
BTW you can remove first exception throwing. Instead of .orElseThrow(() -> new ResourceNotFoundException("the same error message")).stream() use .stream().flatMap(List::stream) which in case of null list (so empty Optional) will create empty stream. So since no value will be found it will be indicated by last orElseThrow. — Pshemo
– Pshemo, Commented Aug 18, 2022 at 15:42

MC Emperor · Accepted Answer · 2025-07-18 09:18:52Z

7

An Optional::ofNullable can be turned into a (possibly empty) Stream, or you can immediately use Stream::ofNullable. And do a flatMap.

Stream.ofNullable(listCanBeNull)
    .flatMap(List::stream)
    .filter(configuration -> configuration.getId().equals(warehouseConfigurationId))
    .findAny()
    .orElseThrow(() -> new ResourceNotFoundException("the same error message"));

edited Jul 18 at 9:18

MC Emperor

23.3k16 gold badges90 silver badges138 bronze badges

answered Aug 18, 2022 at 15:43

Joop Eggen

110k8 gold badges89 silver badges142 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

salerokada Jul 17 at 18:48

It can be also like this: Stream.ofNullable(listCanBeNull) .flatMap(Collection::stream) .filter...

Joop Eggen Jul 18 at 7:24

Streams seems like talking in a foreign language - with mistakes. Correct it.

Makoto · Accepted Answer · 2022-08-18 15:38:18Z

6

Just check if the list is null directly. Streaming elements from a list only makes sense if the list exists in the first place.

if(null != listCanBeNull) {
    // stream things from here
}

answered Aug 18, 2022 at 15:38

Makoto

107k29 gold badges199 silver badges236 bronze badges

2 Comments

Basil Bourque Over a year ago

Or, if ( Objects.nonNull( list ) ) { … }

user85421 Jul 18 at 7:47

simple; expressing almost¹ exactly what I want done; no additional objects needed/being created; no need to know the function of some additional method (¹ - I personally do not like the Yoda Conditions)

Basil Bourque · Accepted Answer · 2025-07-18 17:35:01Z

tl;dr

Objects.requireNonNull( list ).stream() …  // Throws NullPointerException if null.

Details

If you choose to go with a simple null check before streaming, here is an alternative to the null check shown in correct Answer by Makoto.

`Objects.nonNull`

I find a call to Objects.nonNull to be more readable than null != list.

if ( Objects.nonNull( list ) ) { list.stream() … }

`Objects.requireNonNull`

Or automatically throw an exception if the object reference should never be null, with a call to Objects.requireNonNull.

 Objects.requireNonNull( list )  // Throws NullPointerException if null.

This method returns the object you pass (your list), providing for convenient method-chaining.

Objects.requireNonNull( list ).stream() …

You can optionally pass a message to be used in the exception if thrown.

Objects.requireNonNull( list , "message goes here" ).stream() …

Collectives™ on Stack Overflow

Java Streams - check if list is null

3 Answers 3

2 Comments

2 Comments

tl;dr

Details

`Objects.nonNull`

`Objects.requireNonNull`

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

2 Comments

tl;dr

Details

Objects.nonNull

Objects.requireNonNull

Comments

Your Answer

Sign up or log in

Post as a guest

Related

`Objects.nonNull`

`Objects.requireNonNull`