code: public static void flatCopyTo(String prefix, Map<String, Object> sourceMap,
                                    Map<String, String> dstMap) {
          for (Map.Entry<String, Object> entry : sourceMap.entrySet()) {
              String key = prefix + entry.getKey();
              Object value = entry.getValue();
              if (value instanceof String) {
                  dstMap.put(key, (String) value);
              } else if (value instanceof Number) {
                  dstMap.put(key, value.toString());
              } else if (value instanceof Map) {
                  flatCopyTo(key + ".", (Map<String, Object>) value, dstMap);
              }
          }
      }
docs: 扁平化复制
  @param prefix 前缀
  @param sourceMap 原始map
  @param dstMap 目标map