Filter null values after map in Java 8 [duplicate]

问题

This question already has answers here:

Filter values only if not null using lambda in Java8 (6 answers)

Closed 4 years ago.

I'm new in using map and filters in Java 8. I'm currently using Spark ML library for some ML algorithms. I have the following code:

// return a list of `Points`.
List<Points> points = getPoints();
List<LabeledPoint> labeledPoints = points.stream()
                                        .map(point -> getLabeledPoint(point))
                                        .collect(Collectors.toList());

The function getLabeledPoint(Point point) returns a new LabeledPoint if the data is correct or null otherwise. How can I filter (remove) the null LabeledPoint objects after map?

回答1:

There is filter method on Stream:

// return a list of `Points`.
List<Points> points = getPoints();
List<LabeledPoint> labeledPoints = points.stream()
                                    .map(point -> getLabeledPoint(point))
                                    // NOTE the following:
                                    .filter(e -> e != null)
                                    .collect(Collectors.toList());

来源：https://stackoverflow.com/questions/40777874/filter-null-values-after-map-in-java-8