自定义Jackson反序列化程序中的java委托

Question

情况如下：我已经设法让Jackson反序列化了以下泛型ResponseWrapper<T>

static final class ResponseWrapper<T> {
    
    private ResponseData <T> response;
    
    protected static final class ResponseData<T> {
    
        private int    status;
        private T      data;
    
    }
    
}

使用以下ParameterizedTypeReference

public static <T> ParameterizedTypeReference <ResponseWrapper<T>> typeReferenceOf ( Class<T> tClass ) {
    return ParameterizedTypeReference.forType( ParameterizedTypeImpl.make( ResponseWrapper.class, new Type[]{ tClass }, null ) );
}

问题：我需要处理这样一种情况：T的反序列化将失败，因为data的值将不是一个对象，而是一个String。我需要捕获异常并将该值分配给ResponseData中的另一个属性，例如String errorMessage。我的想法是用@JsonDeserialize( using = ResponseDeserializer.class )注释response属性，但我不知道如何正确地实现JsonDeserializer，以便它将反序列化委托给Jackson的实现，并在异常发生时捕获异常

关于更多的上下文，我使用WebClient作为HTTP客户机，并使用进行反序列化的交换Function<ClientResponse, Mono<ResponseWrapper<T>>处理响应

Answer 1

为了获得泛型类型，我有ResponseDeserializer实现ContextualDeserializer

@Override
public JsonDeserializer<?> createContextual ( DeserializationContext context, BeanProperty property ) throws JsonMappingException {

   JavaType wrapperType = property.getType();
   JavaType valueType = wrapperType.containedType(0);
   return new ResponseDeserializer<>( valueType );

}

这使我能够使用特定的JavaType创建反序列化程序的具体实例。以下是完整的解决方案：

private static final class ResponseDeserializer<T> extends JsonObjectDeserializer<ResponseWrapper.ResponseData<T>> implements ContextualDeserializer  {
   
   private final JavaType javaType;

   public ResponseDeserializer ( ) {
       this.javaType = null;
   }
   
   public ResponseDeserializer ( JavaType javaType ) {
       this.javaType = javaType;
   }
   
   @Override
   public JsonDeserializer<?> createContextual ( DeserializationContext context, BeanProperty property ) throws JsonMappingException {

       JavaType wrapperType = property.getType();
       JavaType valueType = wrapperType.containedType(0);
       return new ResponseDeserializer<>( valueType );
       
   }

   @Override
   protected ResponseWrapper.ResponseData<T> deserializeObject ( JsonParser jsonParser, DeserializationContext context, ObjectCodec codec, JsonNode tree ) throws IOException {
       
       int status = tree.get( "status" ).asInt();
       JsonNode dataNode = tree.get( "data" );
       
       try {

           final T data; {
               
               if ( dataNode == null ) {
                   data = null;
               } else {
                   JsonParser dataParser = dataNode.traverse();
                   JsonToken token = dataParser.nextToken(); // handle?
                   data = context.readValue( dataParser, javaType );
               }
               
           };
           
           return new ResponseWrapper.ResponseData<T>( status, data );
           
       } catch ( InvalidDefinitionException e ) {
           
           String errorMessage = dataNode.asText();
           return new ResponseWrapper.ResponseData<T>( status, errorMessage );
           
       }

   }
   
}