在 Java 8 中映射后过滤空值

Filter null values after map in Java 8

提问by cybertextron

I'm new in using mapand filtersin Java 8. I'm currently using Spark MLlibrary for some ML algorithms. I have the following code:

我在使用新的map和filters在Java中8.我目前使用的Spark ML库对于一些ML算法。我有以下代码：

// 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 LabeledPointif the data is correct or null otherwise. How can I filter (remove) the nullLabeledPointobjects after map?

如果数据正确，该函数getLabeledPoint(Point point)返回一个新的，LabeledPoint否则返回空。之后如何过滤（删除）nullLabeledPoint对象map？

回答by Zbynek Vyskovsky - kvr000

There is filtermethod on Stream:

filterStream 上有方法：

// 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());