java - typeinfo 的多态 Jackson 反序列化不适用于枚举

Question

我有以下类作为 JSON 对象的 java 表示:

public class Vehicle
{
   private VehicleType vehicleType;

   private VehicleConfiguration vehicleConfiguration;

   @JsonCreator
   public Vehicle( @JsonProperty("vehicleType")final VehicleType vehicleType,
         @JsonProperty("vehicleConfiguration")final VehicleConfiguration vehicleConfiguration )
   {
      this.vehicleType = vehicleType;
      this.vehicleConfiguration = vehicleConfiguration;
   }

   ...

   @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXTERNAL_PROPERTY, property = "vehicleType")
   @JsonSubTypes({ @JsonSubTypes.Type(value = TruckConfiguration.class, name = "TRUCK"),
         @JsonSubTypes.Type(value = CarConfiguration.class, name = "CAR") })
   public void setVehicleConfiguration(
         final VehicleConfiguration vehicleConfiguration )
   {
      this.vehicleConfiguration = vehicleConfiguration;
   }
}

我使用vehicleType枚举(有两个值TRUCK和CAR)作为外部属性来告诉反序列化器我希望如何反序列化VehicleConfiguration抽象类:要么是CarConfiguration，要么是TruckConfiguration。以下是其他类(不包括样板):

public class CarConfiguration extends VehicleConfiguration
{
   private int numberOfDoors;


   @JsonCreator
   public CarConfiguration( @JsonProperty("numberOfDoors") final int numberOfDoors )
   {
      this.numberOfDoors = numberOfDoors;
   }
}

public class TruckConfiguration extends VehicleConfiguration
{
   private String manufacturer;


   @JsonCreator
   public TruckConfiguration( @JsonProperty("manufacturer") final String manufacturer )
   {
      this.manufacturer = manufacturer;
   }
}

我的测试如下:

@Test
   public void given_when_then() throws IOException
   {
      // GIVEN
      final String json = "{\n"
            + "    \"vehicleType\": \"TRUCK\",\n"
            + "    \"vehicleConfiguration\": {\n"
            + "      \"manufacturer\": \"SCANIA\"\n"
            + "    }\n"
            + "}";

      // WHEN
      ObjectMapper mapper = new ObjectMapper();
      mapper.enableDefaultTyping();

      Vehicle vehicle = mapper.readValue(json, Vehicle.class);

      // THEN
      assertEquals((( TruckConfiguration ) vehicle.getVehicleConfiguration()).getManufacturer(), "SCANIA");
   }

它抛出以下异常:

com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of com.test.Vehicle, problem: argument type mismatch
 at [Source: {
    "vehicleType": "TRUCK",
    "vehicleConfiguration": {
      "manufacturer": "SCANIA"
    }
}; line: 6, column: 1]

    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:277)
    at com.fasterxml.jackson.databind.DeserializationContext.instantiationException(DeserializationContext.java:1441)
    at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.wrapAsJsonMappingException(StdValueInstantiator.java:476)
    at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.rewrapCtorProblem(StdValueInstantiator.java:495)
    at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromObjectWith(StdValueInstantiator.java:276)
    at com.fasterxml.jackson.databind.deser.ValueInstantiator.createFromObjectWith(ValueInstantiator.java:228)
    at com.fasterxml.jackson.databind.deser.impl.PropertyBasedCreator.build(PropertyBasedCreator.java:135)
    at com.fasterxml.jackson.databind.deser.impl.ExternalTypeHandler.complete(ExternalTypeHandler.java:230)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeUsingPropertyBasedWithExternalTypeId(BeanDeserializer.java:937)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeWithExternalTypeId(BeanDeserializer.java:792)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:312)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:148)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3798)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2842)
    at com.test.VehicleTest.given_when_then(VehicleTest.java:44)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: java.lang.IllegalArgumentException: argument type mismatch
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at com.fasterxml.jackson.databind.introspect.AnnotatedConstructor.call(AnnotatedConstructor.java:124)
    at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromObjectWith(StdValueInstantiator.java:274)
    ... 32 more

似乎问题在于枚举vehicleType作为typeInfo:如果我将此字段更改为简单字符串，并运行相同的测试，它就可以正常工作。但在我的设计中，我已经有一个枚举，我需要用它来区分反序列化。

我的临时解决方案是向抽象VehicleConfiguration添加一个vehicleType字段，并使用JsonTypeInfo.As.PROPERTY注释直接在抽象类上设置注释。像这样，它甚至可以与枚举一起使用，但我在vehicleType字段中添加了冗余信息。那么这是解串器的一些错误，还是我遗漏了一些东西？

Answer 1

经过大量谷歌搜索和努力，终于找到了解决方案:删除了构造函数，现在一切正常。