Java 8 – 从一个 Stream中过滤null值

淡淡的烟草味﹌ 2022-06-15 06:12 379阅读 0赞

复习一个`Stream` 包含 `null` 数据的例子.

Java8Examples.java

package com.mkyong.java8; import java.util.List; import java.util.stream.Collectors; import java.util.stream.Stream; public class Java8Examples { public static void main(String[] args) { Stream<String> language = Stream.of("java", "python", "node", null, "ruby", null, "php"); List<String> result = language.collect(Collectors.toList()); result.forEach(System.out::println); } }

output

java
    python
    node
    null   // <--- NULL
    ruby
    null   // <--- NULL
    php

## Solution（解决） ##

为了解决上面的问题，我们使用： `Stream.filter(x -> x!=null)`

Java8Examples.java

package com.mkyong.java8; import java.util.List; import java.util.stream.Collectors; import java.util.stream.Stream; public class Java8Examples { public static void main(String[] args) { Stream<String> language = Stream.of("java", "python", "node", null, "ruby", null, "php"); //List<String> result = language.collect(Collectors.toList()); List<String> result = language.filter(x -> x!=null).collect(Collectors.toList()); result.forEach(System.out::println); } }

output

java
    python
    node
    ruby
    php

另外，过滤器还可以用： `Objects::nonNull`

import java.util.List; List<String> result = language.filter(Objects::nonNull).collect(Collectors.toList());

## References ##

1.  [Objects::nonNull JavaDoc][Objects_nonNull JavaDoc]
2.  [Java 8 Streams filter examples][]
3.  [Java 8 Collectors JavaDoc][]

[Objects_nonNull JavaDoc]: https://docs.oracle.com/javase/8/docs/api/java/util/Objects.html#nonNull-java.lang.Object-
[Java 8 Streams filter examples]: https://www.mkyong.com/java8/java-8-streams-filter-examples/
[Java 8 Collectors JavaDoc]: https://docs.oracle.com/javase/8/docs/api/java/util/stream/Collectors.html