不确定我是否正确理解了这个问题，但是类似的方法可能有效. 尚未检查所有语法，因此某处可能存在一些错误.

Not sure if I understood the question correctly, but something like this might work. Haven't checked all the syntax yet, so there might be some mistake somewhere.

Stream<Map.Entry<String, String>> flatten(Map<String, Object> map) {
  return map.entrySet()
            .stream()
            .flatMap(this::extractValue);         
}

Stream<Map.Entry<String, String>> extractValue(Map.Entry<String, Object> entry) {
   if (entry.getValue() instanceof String) {
      return Stream.of(new AbstractMap.SimpleEntry(entry.getKey(), (String) entry.getValue()));
   } else if (entry.getValue() instanceof Map) {
      return flatten((Map<String, Object>) entry.getValue());
   }
}

那么你可以做:

Map<String, String> flattenedMap = flatten(yourmap)
   .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));