stream collector merge maps

Bonsoir
A force de tâtonner j'ai trouvé une solution. je ne sais pas si elle est optimale mais elle fonctionne.

Code:

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package org.acme;
 
import java.util.*;
import java.util.Map.Entry;
import java.util.function.BinaryOperator;
import java.util.function.Supplier;
import java.util.stream.Collector;
import java.util.stream.Collectors;
import java.util.stream.Stream;
 
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;
 
public class MergeTest {
 
    @Test
    public void testMerge() {
        Map<String, List<String>> mapGlobal = new HashMap<String, List<String>>();
        Map<String, List<String>> mapAdded = new HashMap<String, List<String>>();
 
        mapGlobal.put("a", Arrays.asList("1", "3", "5", "7"));
        mapAdded.put("b", Arrays.asList("10", "30", "50", "70"));
        mapAdded.put("a", Arrays.asList("1", "9", "15"));
 
 
        Map<String, List<String>> other = 
            Stream.of(mapGlobal, mapAdded)
                .flatMap(m -> m.entrySet().stream())
                .collect(Collectors.toMap(
                    Map.Entry::getKey, Map.Entry::getValue, 
                    (t,u) -> Stream.of(t, u).flatMap(List::stream).distinct().collect(Collectors.toList())
                    )
                );
        System.out.println(other);
    }
 
}

Code:

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[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running org.acme.MergeTest
{a=[1, 3, 5, 7, 9, 15], b=[10, 30, 50, 70]}
[

A+JYT