Java 杰克逊：“意外的令牌（VALUE_STRING），预期的 FIELD_NAME：”反序列化空字符串而不是预期的对象时
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Hymanson: "Unexpected token (VALUE_STRING), expected FIELD_NAME:" when deserializing empty string instead of expected object
提问by CtrlF
I'm using Hymanson to deserialize json responses from a server I do not own. I'm using JsonTypeInfo annotations to handle polymorphic data types. Here's the configuration I have on my base type (Thingin this case):
我正在使用 Hymanson 反序列化来自我不拥有的服务器的 json 响应。我正在使用 JsonTypeInfo 注释来处理多态数据类型。这是我对基本类型的配置（Thing在本例中）：
@JsonTypeInfo(
use = JsonTypeInfo.Id.NAME,
include = JsonTypeInfo.As.PROPERTY,
property = "type")
@JsonSubTypes({
@JsonSubTypes.Type(value = Thing.class, name = "Thing"),
@JsonSubTypes.Type(value = FancyThing.class, name = "FancyThing")
})
Everything works great until the server returns an empty string where I am expecting one of these types and then I get one of these:
一切都很好，直到服务器返回一个空字符串，我期待其中一种类型，然后我得到其中一种：
org.codehaus.Hymanson.map.JsonMappingException: Unexpected token (VALUE_STRING), expected FIELD_NAME: missing property 'type' that is to contain type id (for class com.stackoverflow.Thing)
org.codehaus.Hymanson.map.JsonMappingException: Unexpected token (VALUE_STRING), expected FIELD_NAME: missing property 'type' that is to contain type id (for class com.stackoverflow.Thing)
Is there a recommended way of handling cases like this? Like I said, I don't control the server, so I have to handle this client side. I'd rather handle this by configuring the ObjectMapper, but ObjectMapper#configure(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, true)doesn't seem to work the way I had expected. Any ideas?
有没有推荐的处理这种情况的方法？就像我说的，我不控制服务器，所以我必须处理这个客户端。我宁愿通过配置 来处理这个问题ObjectMapper，但ObjectMapper#configure(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, true)似乎并没有像我预期的那样工作。有任何想法吗？
采纳答案by CtrlF
Ok, so sometimes all it takes to get an answer is to ask yourself the right question. It turns out, I think I was looking at an older version of the javadocs, because I discovered @JsonTypeInfo#defaultImpland that has set me on to the right track.
好的，所以有时获得答案所需的只是问自己正确的问题。事实证明，我认为我正在查看 javadoc 的旧版本，因为我发现@JsonTypeInfo#defaultImpl并且这使我走上了正确的轨道。
Now I have something that looks like this:
现在我有一些看起来像这样的东西：
@JsonTypeInfo(
use = JsonTypeInfo.Id.NAME,
include = JsonTypeInfo.As.PROPERTY,
property = "type"
defaultImpl = EmptyThing.class)
@JsonSubTypes({
@JsonSubTypes.Type(value = Thing.class, name = "Thing"),
@JsonSubTypes.Type(value = FancyThing.class, name = "FancyThing")
})
public class Thing {
...
}
public class EmptyThing extends Thing {
public EmptyThing(String s) {
// Hymanson wants a single-string constructor for the default impl
}
}
