杰克逊使用枚举键POJO值反序列化为Map [英] Jackson deserializing into Map with an Enum Key, POJO Value

问题描述

我正在尝试使用Jackson将JSON反序列化为Java POJO.在不泄露机密信息的情况下，这是ObjectMapper的反序列化失败时的示例堆栈跟踪:

I am trying to deserialize JSON into a Java POJO using Jackson. Without giving away confidential information, here is an example stack trace when ObjectMapper's deserialization fails:

org.codehaus.jackson.map.JsonMappingException: Can not construct Map key of type com.example.MyEnum from String "coins": not a valid representation: Can not construct Map key of type com.example.MyEnum from String "coins": not one of values for Enum class

我的JSON看起来像这样:

My JSON looks like this:

"foo": {
    "coins": null,
    ...
}

我要反序列化的类具有以下字段:

And the class I want to deserialize into has this field:

private Map<MyEnum, MyPojo> foo;

我的枚举类型如下:

public enum MyEnum {
    COINS("coins"),
    ...
}

我确实意识到我正在尝试反序列化一个空值.但是我认为这仍然应该起作用:反序列化的结果应该等效于使用foo.put(MyEnum.COINS, null)映射，这确实是有效的Java指令.非常感谢您的帮助，谢谢.

I do realize that I am trying to deserialize a null value. But I believe this should still work: the result of the deserialization should be equivalent to having a Map with foo.put(MyEnum.COINS, null), which is indeed a valid Java instruction. Help is much appreciated, thanks in advance.

推荐答案

除了提供一种好的解决方案(工厂方法)外，还有两种其他方法:

In addition to one good solution presented (factory method), there are 2 other ways:

• 如果'MyEnum.toString()'返回"coins"，您可以使用ObjectMapper.enable(DeserializationFeature.READ_ENUMS_USING_TO_STRING)
使Jackson在"name()"上使用"toString()"
• 您可以添加其他方法以返回要使用的id，并用@JsonValue注释标记该方法(实际上，您也可以在toString()上使用该方法，而不是启用上述功能)-如果该注释存在，该方法返回的值用作ID.

• If 'MyEnum.toString()' would return "coins", you can make Jackson use "toString()" over "name()"with ObjectMapper.enable(DeserializationFeature.READ_ENUMS_USING_TO_STRING)
• You could add some other method to return id to use, and mark that method with @JsonValue annotation (you can actually use that on toString() as well, instead of enabling above feature) -- if that annotation exists, value returned by that method is used as the id.

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