如何展开List<Map>、按映射键分组和按映射值还原

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class MapListExample {
    public static void main(String[] args) {
        // 创建一个包含多个Map的List
        List<Map<String, String>> mapList = new ArrayList<>();
        
        // 添加Map到List中
        Map<String, String> map1 = new HashMap<>();
        map1.put("key1", "value1");
        map1.put("key2", "value2");
        mapList.add(map1);
        
        Map<String, String> map2 = new HashMap<>();
        map2.put("key3", "value3");
        map2.put("key4", "value4");
        mapList.add(map2);
        
        // 展开List<Map>
        List<Map.Entry<String, String>> flattenedList = new ArrayList<>();
        for (Map<String, String> map : mapList) {
            for (Map.Entry<String, String> entry : map.entrySet()) {
                flattenedList.add(entry);
            }
        }
        
        // 按映射键分组
        Map<String, List<Map.Entry<String, String>>> groupedMap = new HashMap<>();
        for (Map.Entry<String, String> entry : flattenedList) {
            String key = entry.getKey();
            if (!groupedMap.containsKey(key)) {
                groupedMap.put(key, new ArrayList<>());
            }
            groupedMap.get(key).add(entry);
        }
        
        // 按映射值还原
        List<Map<String, String>> restoredList = new ArrayList<>();
        for (Map.Entry<String, List<Map.Entry<String, String>>> entry : groupedMap.entrySet()) {
            Map<String, String> restoredMap = new HashMap<>();
            for (Map.Entry<String, String> mapEntry : entry.getValue()) {
                restoredMap.put(mapEntry.getKey(), mapEntry.getValue());
            }
            restoredList.add(restoredMap);
        }
        
        // 打印展开后的List<Map>
        System.out.println("展开后的List<Map>:");
        for (Map.Entry<String, String> entry : flattenedList) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
        
        // 打印按映射键分组后的Map列表
        System.out.println("按映射键分组后的Map列表:");
        for (Map.Entry<String, List<Map.Entry<String, String>>> entry : groupedMap.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
        
        // 打印按映射值还原后的List<Map>
        System.out.println("按映射值还原后的List<Map>:");
        for (Map<String, String> map : restoredList) {
            for (Map.Entry<String, String> entry : map.entrySet()) {
                System.out.println(entry.getKey() + ": " + entry.getValue());
            }
        }
    }
}