Better Filtering on Java Streams

Question

I need to run filtering on nested Lists and return a List of items from back

I will put a sample code here with my model

import lombok.Data;

import java.util.List;
import java.util.stream.Collectors;

class Scratch {
    public static void main(String[] args) {

        ParentModel parent = new ParentModel();
        List<Information> informationList = parent.getChildDatas().stream()
                //Filtering null && empty grandchild
                .filter(childData -> childData.getGrandChildDatas() !=null && !childData.getGrandChildDatas().isEmpty())
                .flatMap(childData -> childData.getGrandChildDatas().stream() )
                //Filtering null && empty information
                .filter(grandChild -> grandChild.getInformations() !=null && !grandChild.getInformations().isEmpty())
                .flatMap(grandChild-> grandChild.getInformations().stream())
                //filtering key
                .filter(information -> information.getKey().equals("SOMETHING"))
                .collect(Collectors.toList());

    }

    @Data
    static class ParentModel {
        private List<ChildModel> childDatas;
    }

    @Data
    static class ChildModel {
        private List<GrandChildModel> grandChildDatas;
    }

    @Data
    static class GrandChildModel {
        private List<Information> informations;
    }

    @Data
    static class Information{
        private String info1;
        private String info2;
        private String key;
    }
}

So here you can see, I'm filtering and mapping it back to child streams two times.

Is there alternate way to achieve what I'm trying to do here ??

I have rolled back your latest edit. Please see "What should I do when someone answers my question?", especially, the "What should I not do?" section. — AJNeufeld
– AJNeufeld, Commented Feb 4, 2020 at 16:15

AJNeufeld · Accepted Answer · 2020-02-03 15:02:21Z

First, you should avoid using null to represent an empty list. Use an actual empty list, or even Collections.emptyList(), which is a immutable singleton. This will avoid the need for null checks.

Second, you are filtering by getting a sub attribute, checking conditions on that object, then requesting the same sub attribute in the next step. Instead, you should map to the sub attribute, then filter & process.

    ...
    .map(ChildModel::getChildrenDatas)
    .filter(data -> data != null && !data.isEmpty())
    .flatMap(List::stream)
    ...

Third, the .isEmpty() check is unnecessary, as .flatMap works fine with an empty stream.

   ...
    .map(ChildModel::getChildrenDatas)
    .filter(Objects::nonNull)
    .flatMap(List::stream)
    ...

Again, if you don’t use null to represent empty lists, the filter line can be removed entirely.

Unfortunately I wish to avoid null, but the data and data model is provided by 3rd party wrapped in their client code for their server. So i need to live with that — edwin
– edwin, Commented Feb 3, 2020 at 15:15

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