如何使用Java8流将Map<X、Map<Y、Z>>转换为Map<Y、Map<X、Z>>

import java.util.HashMap;
import java.util.Map;
import java.util.stream.Collectors;

public class MapTransformationExample {
    public static void main(String[] args) {
        // 创建一个示例的嵌套Map结构
        Map<String, Map<Integer, String>> nestedMap = new HashMap<>();
        Map<Integer, String> innerMap1 = new HashMap<>();
        innerMap1.put(1, "Value1");
        innerMap1.put(2, "Value2");
        nestedMap.put("Key1", innerMap1);
        Map<Integer, String> innerMap2 = new HashMap<>();
        innerMap2.put(3, "Value3");
        innerMap2.put(4, "Value4");
        nestedMap.put("Key2", innerMap2);
        
        // 使用Java 8流将嵌套的Map转换为新的Map结构
        Map<Integer, Map<String, String>> transformedMap = nestedMap.entrySet().stream()
                .flatMap(outerEntry -> outerEntry.getValue().entrySet().stream()
                        .map(innerEntry -> new InnerMapEntry(outerEntry.getKey(), innerEntry.getKey(), innerEntry.getValue())))
                .collect(Collectors.groupingBy(InnerMapEntry::getInnerKey,
                        Collectors.toMap(InnerMapEntry::getOuterKey, InnerMapEntry::getValue)));
        
        // 打印转换后的Map结构
        System.out.println(transformedMap);
    }
    
    // 辅助类，用于存储内部Map的键值对
    private static class InnerMapEntry {
        private final String outerKey;
        private final int innerKey;
        private final String value;
        
        public InnerMapEntry(String outerKey, int innerKey, String value) {
            this.outerKey = outerKey;
            this.innerKey = innerKey;
            this.value = value;
        }
        
        public String getOuterKey() {
            return outerKey;
        }
        
        public int getInnerKey() {
            return innerKey;
        }
        
        public String getValue() {
            return value;
        }
    }
}

{1={Key1=Value1}, 2={Key1=Value2}, 3={Key2=Value3}, 4={Key2=Value4}}