如何实现哈希映射以支持多维度映射和前缀查询？

import java.util.*;
import java.util.stream.*;

class Dimension {
    String a, b; // 简化维度

    public Dimension(String a, String b) {
        this.a = a;
        this.b = b;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Dimension dimension = (Dimension) o;
        return Objects.equals(a, dimension.a) && Objects.equals(b, dimension.b);
    }

    @Override
    public int hashCode() {
        return Objects.hash(a, b);
    }
}

public class MultiDimensionHashMap {
    Map<Dimension, String> hashMap = new HashMap<>();

    public void put(String a, String b, String uniqueId) {
        hashMap.put(new Dimension(a, b), uniqueId);
    }

    public List<String> get(String prefix) {
        return hashMap.entrySet().stream()
                .filter(entry -> entry.getKey().a.equals(prefix))
                .map(Map.Entry::getValue)
                .collect(Collectors.toList());
    }

    public static void main(String[] args) {
        MultiDimensionHashMap map = new MultiDimensionHashMap();
        map.put("a", "b", "u1");
        map.put("a", "c", "u2");
        map.put("x", "y", "v1");

        System.out.println(map.get("a")); // Output: [u1, u2]
    }
}