我必须实例化一个类,该类使用@class中的信息从JSON扩展了抽象类,如下所示.

"name": {
  "health": "xxx",
  "animal": {
    "_class": "com.example.Dog",
    "height" : "20"
    "color" : "white"
  }
},

这里的抽象类是动物,而狗则扩展了动物类.因此,使用@class中的信息,我们可以直接实例化dog吗.这也是我在restTemplate中得到的响应

ResponseEntity<List<SomeListName>> response = restTemplate.exchange("http://10.150.15.172:8080/agencies", HttpMethod.GET, request, responseType);

执行此行时,将出现以下错误.
由于POJO类是自动生成的,因此无法使用@JsonTypeInfo之类的注释

我正在使用Spring Boot和Maven.
控制台中出现此错误.

Could not read JSON: Can not construct instance of “MyPOJO”, problem: abstract types either need to be mapped to concrete types, have custom deserializer, or be instantiated with additional type information

解决方法:

通过遵循MixIn’s,可以使用@JsonTypeInfo批注,而不考虑生成类的事实.

“mix-in annotations are”: a way to associate annotations with
classes, without modifying (target) classes themselves.

That is, you can:

Define that annotations of a mix-in class (or interface) will be used
with a target class (or interface) such that it appears as if the
target class had all annotations that the mix-in class has (for
purposes of configuring serialization / deserialization)

因此,您可以编写AnimalMixIn类,例如

@JsonTypeInfo(  
    use = JsonTypeInfo.Id.NAME,  
    include = JsonTypeInfo.As.PROPERTY,  
    property = "_class")  
@JsonSubTypes({  
    @Type(value = Cat.class, name = "com.example.Cat"),  
    @Type(value = Dog.class, name = "com.example.Dog") })  
abstract class AnimalMixIn  
{  

}  

并配置您的解串器

    ObjectMapper mapper = new ObjectMapper();  
    mapper.getDeserializationConfig().addMixInAnnotations(  
    Animal.class, AnimalMixIn.class);

由于您使用的是Spring Boot,因此可以查看以下博客文章,以了解如何自定义ObjectMapper以使用MixIns,Customizing the Jackson Object Mapper,尤其要注意Jackson2ObjectMapperBuilder的mixIn方法

在RestTemplate中使用自定义的ObjectMapper应该通过转换器进行设置,例如

    RestTemplate restTemplate = new RestTemplate();
    List<HttpMessageConverter<?>> messageConverters = new ArrayList<>();
    MappingJackson2HttpMessageConverter jsonMessageConverter = new MappingJackson2HttpMessageConverter();
    jsonMessageConverter.setObjectMapper(objectMapper);
    messageConverters.add(jsonMessageConverter);
    restTemplate.setMessageConverters(messageConverters);
    return restTemplate;