I have a list of objects say car
. I want to filter this list based on some parameter using Java 8. But if the parameter is null
, it throws NullPointerException
. How to filter out null values?
Current code is as follows
requiredCars = cars.stream().filter(c -> c.getName().startsWith("M"));
This throws NullPointerException
if getName()
returns null
.
This question is related to
java
lambda
nullpointerexception
null
java-8
The proposed answers are great. Just would like to suggest an improvement to handle the case of null list using Optional.ofNullable
, new feature in Java 8:
List<String> carsFiltered = Optional.ofNullable(cars)
.orElseGet(Collections::emptyList)
.stream()
.filter(Objects::nonNull)
.collect(Collectors.toList());
So, the full answer will be:
List<String> carsFiltered = Optional.ofNullable(cars)
.orElseGet(Collections::emptyList)
.stream()
.filter(Objects::nonNull) //filtering car object that are null
.map(Car::getName) //now it's a stream of Strings
.filter(Objects::nonNull) //filtering null in Strings
.filter(name -> name.startsWith("M"))
.collect(Collectors.toList()); //back to List of Strings
You can do this in single filter step:
requiredCars = cars.stream().filter(c -> c.getName() != null && c.getName().startsWith("M"));
If you don't want to call getName()
several times (for example, it's expensive call), you can do this:
requiredCars = cars.stream().filter(c -> {
String name = c.getName();
return name != null && name.startsWith("M");
});
Or in more sophisticated way:
requiredCars = cars.stream().filter(c ->
Optional.ofNullable(c.getName()).filter(name -> name.startsWith("M")).isPresent());
In this particular example I think @Tagir is 100% correct get it into one filter and do the two checks. I wouldn't use Optional.ofNullable
the Optional stuff is really for return types not to be doing logic... but really neither here nor there.
I wanted to point out that java.util.Objects
has a nice method for this in a broad case, so you can do this:
cars.stream()
.filter(Objects::nonNull)
Which will clear out your null objects. For anyone not familiar, that's the short-hand for the following:
cars.stream()
.filter(car -> Objects.nonNull(car))
To partially answer the question at hand to return the list of car names that starts with "M"
:
cars.stream()
.filter(car -> Objects.nonNull(car))
.map(car -> car.getName())
.filter(carName -> Objects.nonNull(carName))
.filter(carName -> carName.startsWith("M"))
.collect(Collectors.toList());
Once you get used to the shorthand lambdas you could also do this:
cars.stream()
.filter(Objects::nonNull)
.map(Car::getName) // Assume the class name for car is Car
.filter(Objects::nonNull)
.filter(carName -> carName.startsWith("M"))
.collect(Collectors.toList());
Unfortunately once you .map(Car::getName)
you'll only be returning the list of names, not the cars. So less beautiful but fully answers the question:
cars.stream()
.filter(car -> Objects.nonNull(car))
.filter(car -> Objects.nonNull(car.getName()))
.filter(car -> car.getName().startsWith("M"))
.collect(Collectors.toList());
you can use this
List<Car> requiredCars = cars.stream()
.filter (t-> t!= null && StringUtils.startsWith(t.getName(),"M"))
.collect(Collectors.toList());
Leveraging the power of java.util.Optional#map()
:
List<Car> requiredCars = cars.stream()
.filter (car ->
Optional.ofNullable(car)
.map(Car::getName)
.map(name -> name.startsWith("M"))
.orElse(false) // what to do if either car or getName() yields null? false will filter out the element
)
.collect(Collectors.toList())
;
You just need to filter the cars that have a null
name:
requiredCars = cars.stream()
.filter(c -> c.getName() != null)
.filter(c -> c.getName().startsWith("M"));
Source: Stackoverflow.com