I see that Guava has isNullOrEmpty utility method for Strings
Strings.isNullOrEmpty(str)
Do we have anything similar for Lists? Something like
Lists.isNullOrEmpty(list)
which should be equivalent to
list == null || list.isEmpty()
Also, do we have anything similar for Arrays? Something like
Arrays.isNullOrEmpty(arr)
which should be equivalent to
arr == null || arr.length == 0
No, this method does not exist in Guava and is in fact in our "idea graveyard."
We don't believe that "is null or empty" is a question you ever really want to be asking about a collection.
If a collection might be null, and null should be treated the same as empty, then get all that ambiguity out of the way up front, like this:
Set<Foo> foos = NaughtyClass.getFoos();
if (foos == null) {
foos = ImmutableSet.of();
}
or like this (if you prefer):
Set<Foo> foos = MoreObjects.firstNonNull(
NaughtyClass.getFoos(), ImmutableSet.<Foo>of());
After that, you can just use .isEmpty() like normal. Do this immediately upon calling the naughty API and you've put the weirdness behind you, instead of letting it continue on indefinitely.
And if the "null which really means empty collection" is not being returned to you, but passed to you, your job is easy: just let a NullPointerException be thrown, and make that caller shape up.
One thing you will tend to find throughout Guava is that they tend to be very antagonistic toward nulls. The authors want to discourage you from using null as much as you probably do, and providing utility methods to make it easier to use null would be counterproductive against this end.
If you want to use Guava's paradigm, consider if the source of this collection (or array) really ought to optionally return null. If not, consider marking it @NonNull and return empty collections instead of null. Or as a parameter to a function that is expecting no null-valued lists, consider using Preconditions.checkNotNull, which throws an exception if a null is (unexpectedly) passed in.
If null really is legitimate, list == null || list.isEmpty() is not that hard.
Spring Framework has specialized util class called CollectionUtils. And the method you are looking for is: org.springframework.util.CollectionUtils.isEmpty. It returns true for null and empty collections.
And for arrays there is org.springframework.util.ObjectUtils.isEmpty method which behaves pretty the same.
Apache CollectionUtils 4 has a method CollectionUtils.emptyIfNull() that returns a empty list if the collection is null. This is very useful in a foreach loop, so you dont need to do a null check before iterating
My solution is : MoreObjects.firstNonNull(list, Collections. emptyList())
I am using Guava MoreObjects with JDK Collections.
@Test
public void listnull() {
List<String> list = null;
for (String str : MoreObjects.firstNonNull(list, Collections.<String> emptyList())) {
System.out.println(str);
}
list = new ArrayList<String>();
list.add("http://stackoverflow.com/");
for (String str : MoreObjects.firstNonNull(list, Collections.<String> emptyList())) {
System.out.println(str);
}
}
