キーで重複を削除するやつ

Utils.java

package io.git.hashibutogarasu;

import org.jetbrains.annotations.NotNull;

import java.util.List;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;

public class Utils {
    public static <T> List<T> distinctByKey(@NotNull List<T> list, Function<? super T, ?> keyExtractor) {
        Set<Object> seen = ConcurrentHashMap.newKeySet();
        seen.addAll(list);

        return list.stream()
                .filter(t -> seen.add(keyExtractor.apply(t)))
                .toList();
    }
}