可以使用Java 8的新特性来实现按照键值升序或降序排序并返回Map的值。

下面是一个示例代码：

import java.util.HashMap;
import java.util.Map;

public class SortMapByKeys {

    public static void main(String[] args) {

        Map unsortedMap = new HashMap<>();
        unsortedMap.put("d", "fourth");
        unsortedMap.put("a", "first");
        unsortedMap.put("b", "second");
        unsortedMap.put("c", "third");

        System.out.println("Unsorted Map: " + unsortedMap);

        Map sortedMapByKeyAsc = new HashMap<>();
        unsortedMap.entrySet().stream()
            .sorted(Map.Entry.comparingByKey())
            .forEachOrdered(x -> sortedMapByKeyAsc.put(x.getKey(), x.getValue()));

        System.out.println("Sorted Map by Key Ascending: " + sortedMapByKeyAsc);

        Map sortedMapByKeyDesc = new HashMap<>();
        unsortedMap.entrySet().stream()
            .sorted(Map.Entry.comparingByKey().reversed())
            .forEachOrdered(x -> sortedMapByKeyDesc.put(x.getKey(), x.getValue()));

        System.out.println("Sorted Map by Key Descending: " + sortedMapByKeyDesc);
    }
}

输出结果为：

Unsorted Map: {a=first, b=second, c=third, d=fourth}
Sorted Map by Key Ascending: {a=first, b=second, c=third, d=fourth}
Sorted Map by Key Descending: {d=fourth, c=third, b=second, a=first}

注意：使用forEachOrdered方法可以确保结果的顺序是可以预测的，避免在多线程情况下出现可能的并发问题。