@JsonTypeInfo屬性在POJO反序列化過程中被忽略

Question

我使用@JsonTypeInfo指示Jackson 2.1.0在'discriminator'屬性中查找具體的類型信息。這很有效，但是在反序列化過程中，歧義屬性並未設置爲POJO。

根據同時傑克遜的Javadoc（com.fasterxml.jackson.annotation.JsonTypeInfo.Id），它應該：

/** 
* Property names used when type inclusion method ({@link As#PROPERTY}) is used 
* (or possibly when using type metadata of type {@link Id#CUSTOM}). 
* If POJO itself has a property with same name, value of property 
* will be set with type id metadata: if no such property exists, type id 
* is only used for determining actual type. 
*<p> 
* Default property name used if this property is not explicitly defined 
* (or is set to empty String) is based on 
* type metadata type ({@link #use}) used. 
*/ 
public String property() default ""; 

這裏是一個failling測試

@Test 
public void shouldDeserializeDiscriminator() throws IOException { 

    ObjectMapper mapper = new ObjectMapper(); 
    Dog dog = mapper.reader(Dog.class).readValue("{ \"name\":\"hunter\", \"discriminator\":\"B\"}"); 

    assertThat(dog).isInstanceOf(Beagle.class); 
    assertThat(dog.name).isEqualTo("hunter"); 
    assertThat(dog.discriminator).isEqualTo("B"); //FAILS 
} 

@JsonTypeInfo(
     use = JsonTypeInfo.Id.NAME, 
     include = JsonTypeInfo.As.PROPERTY, 
     property = "discriminator") 
@JsonSubTypes({ 
     @JsonSubTypes.Type(value = Beagle.class, name = "B"), 
     @JsonSubTypes.Type(value = Loulou.class, name = "L") 
}) 
private static abstract class Dog { 
    @JsonProperty("name") 
    String name; 
    @JsonProperty("discriminator") 
    String discriminator; 
} 

private static class Beagle extends Dog { 
} 

private static class Loulou extends Dog { 
} 

任何想法？

Answer 1

使用 '可見' 屬性，像這樣：

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, 
    include = JsonTypeInfo.As.PROPERTY, 
    property = "discriminator", visible=true) 

然後將暴露類型屬性;默認情況下它們不可見，因此不需要爲此元數據添加顯式屬性。