在给定一个int的int中设置位1-3，只需要根据需要设置位1-3(set bits 1-3 in an int given an int with only bits 1-3 set as desired)

 JSON规范表明重复项不被认为是有效的，但解析器不需要对它们做任何事情。 从实际角度来看，跟踪所有看到的属性会增加开销，这在流解析器级别可能没有意义。 
 
 至于Jackson，它曾经在数据绑定级别进行重复检测，但我认为此时尚未启用。 在处理地图时可以相当容易地添加它。 如果这是你想要的东西，提交功能请求或询问用户列表可能是有意义的（尤其是看其他人是否也想要这个功能，使其更有可能很快被添加）。 
 
 如果您只想进行验证，则可以创建Map子类，使其在重复时抛出异常。 或者，只需在子类中设置一个标志，您可以根据需要进行检查。 

JSON specification indicates duplicates are not consider valid, but parsers are not required to do anything about them. From practical perspective, keeping track of all seen properties adds overhead, which may not make sense at streaming parser level.
 
As to Jackson, it used to have duplicate detection at data binding level, but I think that is not enabled at this point. It could be added fairly easily when dealing with Maps. If this is something you would want, filing a feature request or asking on user list might make sense (esp. to see if others would want this feature too, making it more likely to get added soon).
 
If all you want to do is just validation, you could create a Map subclass, make it throw exception on duplicate. Or, just set a flag in sub-class that you can check if you prefer.