杰克逊反序列化抽象类 [英] Jackson Deserialize Abstract Classes
问题描述
我正在尝试使用JSON ObjectMapper反序列化对象。我在尝试反序列化时看到以下错误
I am trying to deserialize an object using JSON ObjectMapper. I see the below error when trying to deserialize
com.fasterxml.jackson.databind.JsonMappingException:无法构造
实例com.phoenix.types.OrderItem:
抽象类型需要映射到具体类型,具有自定义
反序列化器,或者在[来源:
java.io.StringReader @中包含其他类型信息4bb33f74; line:112,column:7](通过
参考链:
com.phoenix.types.GenerateRequest [order] - > com.phoenix.types.Order [orderItems] - > Object [] [0])
at
com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:261)
at
com.fasterxml.jackson.databind。 DeserializationContext.instantiationException(DeserializationContext.java:1456)
at
com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1012)
at
com.fasterxml。 jackson.databind.deser.AbstractDeserializer.deserialize(AbstractDeserializer.java:149)
at
com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:196)
at
com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:20)
at
com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize (SETT ableBeanProperty.java:499)
at
com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:101)
at
com.fasterxml。 jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:276)
at
com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:140)
at
com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:499)
at
com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty) .java:101)
at
com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:276)
at
com.fasterxml.jackson.databind .deser.BeanDeserializer.deserialize(BeanDeserializer.java:140)
at
com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3789)
at
com .fasterxml.jackson.databind .ObjectMapper.readValue(ObjectMapper.java:2833)
com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of com.phoenix.types.OrderItem: abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information at [Source: java.io.StringReader@4bb33f74; line: 112, column: 7] (through reference chain: com.phoenix.types.GenerateRequest["order"]->com.phoenix.types.Order["orderItems"]->Object[][0]) at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:261) at com.fasterxml.jackson.databind.DeserializationContext.instantiationException(DeserializationContext.java:1456) at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1012) at com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserialize(AbstractDeserializer.java:149) at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:196) at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:20) at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:499) at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:101) at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:276) at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:140) at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:499) at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:101) at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:276) at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:140) at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3789) at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2833)
我遇到了这个 post ,用于执行多态反序列化。这基本上提供了解决上面列出的错误的解决方案。我用于反序列化的类(在本例中为OrderItem等)是jar文件的一部分。但是有一种方法可以在尝试反序列化时将JsonDeserialize定义为objectmapper的一部分,而不是向类本身添加注释,因为我无法访问它。
I came across this post for performing polymorphic deserialization. This basically provides the solution for resolving the error listed above. The classes (In this instance OrderItem etc) that I am using for deserialization are part of a jar file. However is there a way to define JsonDeserialize as part of objectmapper when trying to deserialize instead of adding annotation to the class itself as I don't have access to it.
推荐答案
是的,你可以自己编写自定义解串器抽象类。这个反序列化器必须确定JSON代表哪个具体类,并实例化它的一个实例。
Yes, you can write your own Custom Deserializer for the abstract class. This deserializer will have to determine which concrete class the JSON represents, and instantiate an instance of it.
这可能是更惯用的方法,但这里有一个快速和肮脏的例子:
There is likely a more idiomatic way of doing this, but here is a quick-and-dirty example:
public class Test {
public static void main(String... args) throws IOException {
final ObjectMapper mapper = new ObjectMapper();
final SimpleModule module = new SimpleModule();
module.addDeserializer(Animal.class, new AnimalDeserializer());
mapper.registerModule(module);
final String json = "{\"aGoodBoy\": true}";
final Animal animal = mapper.readValue(json, Animal.class);
System.out.println(animal.talk());
}
public static abstract class Animal {
public abstract String talk();
}
public static class Fish extends Animal {
@Override
public String talk() {
return "blub blub I'm a dumb fish";
}
}
public static class Dog extends Animal {
public boolean aGoodBoy;
@Override
public String talk() {
return "I am a " + (aGoodBoy ? "good" : "bad") + " dog";
}
}
public static class AnimalDeserializer extends StdDeserializer<Animal> {
protected AnimalDeserializer() {
this(null);
}
protected AnimalDeserializer(final Class<?> vc) {
super(vc);
}
@Override
public Animal deserialize(final JsonParser parser, final DeserializationContext context)
throws IOException, JsonProcessingException {
final JsonNode node = parser.getCodec().readTree(parser);
final ObjectMapper mapper = (ObjectMapper)parser.getCodec();
if (node.has("aGoodBoy")) {
return mapper.treeToValue(node, Dog.class);
} else {
return mapper.treeToValue(node, Fish.class);
}
}
}
}
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