- Filtering a Stream of Optionals in Java (With Examples)
- 1. Introduction
- 2. Java 8 — Using filter()
- 3. Java 8 — Using flatMap()
- 4. Java 9 Optional stream() method — Optional::stream
- 5. Conclusion
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Filtering a Stream of Optionals in Java (With Examples)
A quick and practical guide to filtering Streams of Optionals in Java 8 and Java 9 (With Examples).
1. Introduction
In this article, You’ll be learning how to remove or filter the non-empty values from Stream of Optionals from Optional API.
Usually, you work with Stream of Strings or Stream of custom objects. But, there are some cases where you frequently work with Optional values.
Java 8 has come up with a new Optional API which is to avoid the NullPointerExceptions and others as well. Actually, our real value will be wrapped into an Optional instance.
Removing the empty or nullable values from the list can be done in multiple ways in Java 8 and Java 9 concepts.
We’ll’ be working on the List> instance in this whole tutorial.
List> optionalList = Arrays.asList(Optional.of("hello"), Optional.empty(), Optional.of("world"), Optional.empty(), Optional.of("welcome to JavaProgramTo.com blog"));
This list has 5 Optional values and among those 3 are having string values, reaming two are empty optional.
Our intention is to remove the empty values from the List of Optionals.
2. Java 8 — Using filter()
In the first approach, We use the stream filter() method that takes the Predicate condition.
In the predicate, Call one of the Optional methods isPresent() method returns if the value inside the optional is not null. Returns false if the value is null.
If the isPresent() returns true, next use Optional::get method to retrieve the actual value.
package com.javaprogramto.java8.streams.optionals.filtering; import java.util.Arrays; import java.util.List; import java.util.Optional; import java.util.stream.Collectors; public class OptionalNonNullExample < public static void main(String[] args) < List> optionalList = Arrays.asList( Optional.of("hello"), Optional.empty(), Optional.of("world"), Optional.empty(), Optional.of("welcome to JavaProgramTo.com blog")); List nonEmptyValuesList = optionalList .stream() .filter(o -> o.isPresent()) .map(Optional::get) .collect(Collectors.toList()); System.out.println(nonEmptyValuesList); > >
Look at the output, thas filtered out Empty Optional values from it and converted the Stream> to List .
3. Java 8 — Using flatMap()
In the second approach, Java 8 Stream API has another useful method flatMap() that returns Stream and takes Function as an argument.
In our example, we are using flatMap() method to covert non null Optional value to Stream and empty Optional to Empty stream using Stream.empty() method.
package com.javaprogramto.java8.streams.optionals.filtering; import java.util.Arrays; import java.util.List; import java.util.Optional; import java.util.stream.Collectors; import java.util.stream.Stream; public class OptionalNonNullFlatMapEample < public static void main(String[] args) < List> optionalList = Arrays.asList( Optional.of("hello"), Optional.empty(), Optional.of("world"), Optional.empty(), Optional.of("welcome to"), Optional.of("JavaProgramTo.com")); System.out.println("optionalList values : "+optionalList); List nonEmptyValuesList = optionalList .stream() .flatMap(optional -> optional.isPresent() ? Stream.of(optional.get()) : Stream.empty()) .collect(Collectors.toList()); System.out.println(nonEmptyValuesList); > >
[optionalList values : [Optional[hello], Optional.empty, Optional[world], Optional.empty, Optional[welcome to], Optional[JavaProgramTo.com]]
[hello, world, welcome to, JavaProgramTo.com]]
4. Java 9 Optional stream() method — Optional::stream
In the last approach, Java 9 has come up with a new method stream() in Optional class to covert an Optional into Stream.
Optional.stream() —> If a value is present, returns a sequential Stream containing only that value, otherwise returns an empty Stream.
package com.javaprogramto.java8.streams.optionals.filtering; import java.util.Arrays; import java.util.List; import java.util.Optional; import java.util.stream.Collectors; import java.util.stream.Stream; public class OptionalStreamFlatMapEample < public static void main(String[] args) < List> optionalList = Arrays.asList( Optional.of("hello"), Optional.empty(), Optional.of("world"), Optional.empty(), Optional.of("welcome to"), Optional.of("JavaProgramTo.com")); System.out.println("optionalList values : "+optionalList); List nonEmptyValuesList = optionalList .stream() .flatMap(Optional.stream()) .collect(Collectors.toList()); System.out.println(nonEmptyValuesList); > >
5. Conclusion
In this article, You’ve seen how to remove the empty Optional values from Stream in Java 8 and Java 9.
All the code is shown in this article is over GitHub.
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