Java 8 Streams - Collectors.collectingAndThen Examples

Java 8 Streams Java Java API 

Class:

java.util.stream.Collectors

Method:

public static <T,A,R,RR> Collector<T,A,RR> collectingAndThen(Collector<T,A,R> downstream,
                                                             Function<R,RR> finisher)

Adapts a Collector to perform an additional finishing transformation.

Type Parameters:

T - the type of the input elements

A - intermediate accumulation type of the downstream collector

R - result type of the downstream collector

RR - result type of the resulting collector

Parameters:

downstream - a collector

finisher - a function to be applied to the final result of the downstream collector

Returns:

a collector which performs the action of the downstream collector, followed by an additional finishing step

Examples

The method Collectors#collectingAndThen collects each element per provided downStream collector and converts the type R (which returned from the downstream collector) to a final resultant type RR.

package com.logicbig.example.collectors;

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

public class CollectingAndThenExample {
    public static void main (String[] args) {
        Stream<String> s = Stream.of("apple", "banana", "orange");
        List<String> synchronizedList = s.collect(Collectors.collectingAndThen(
                            Collectors.toList(), Collections::synchronizedList));
        System.out.println(synchronizedList);
    }
}

Output

[apple, banana, orange]

Original Post