Spring Data Rest: #Autowire in Custom JsonDeserializer - spring-boot

Question

I am trying to autowire a component into a custom JsonDeserializer but cannot get it right even with the following suggestions I found:
Autowiring in JsonDeserializer: SpringBeanAutowiringSupport vs HandlerInstantiator
Right way to write JSON deserializer in Spring or extend it
How to customise the Jackson JSON mapper implicitly used by Spring Boot?
Spring Boot Autowiring of JsonDeserializer in Integration test
My final goal is to accept URLs to resources in different microservices and store only the ID of the resource locally. But I don't want to just extract the ID from the URL but also verify that the rest of the URL is correct.
I have tried many things and lost track a bit of what I tried but I believe I tried everything mentioned in the links above. I created tons of beans for SpringHandlerInstantiator, Jackson2ObjectMapperBuilder, MappingJackson2HttpMessageConverter, RestTemplate and others and also tried with setting the SpringHandlerInstantiator in RepositoryRestConfigurer#configureJacksonObjectMapper.
I am using Spring Boot 2.1.6.RELEASE which makes me think something might have changed since some of the linked threads are quite old.
Here's my last attempt:
#Configuration
public class JacksonConfig {
#Bean
public HandlerInstantiator handlerInstantiator(ApplicationContext applicationContext) {
return new SpringHandlerInstantiator(applicationContext.getAutowireCapableBeanFactory());
}
}
#Configuration
public class RestConfiguration implements RepositoryRestConfigurer {
#Autowired
private Validator validator;
#Autowired
private HandlerInstantiator handlerInstantiator;
#Override
public void configureValidatingRepositoryEventListener(ValidatingRepositoryEventListener validatingListener) {
validatingListener.addValidator("beforeCreate", validator);
validatingListener.addValidator("beforeSave", validator);
}
#Override
public void configureJacksonObjectMapper(ObjectMapper objectMapper) {
objectMapper.setHandlerInstantiator(handlerInstantiator);
}
}
#Component
public class RestResourceURLSerializer extends JsonDeserializer<Long> {
#Autowired
private MyConfig config;
#Override
public Long deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
ServiceConfig serviceConfig = config.getServices().get("identity");
URI serviceUri = serviceConfig.getExternalUrl();
String servicePath = serviceUri.getPath();
URL givenUrl = p.readValueAs(URL.class);
String givenPath = givenUrl.getPath();
if (servicePath.equals(givenPath)) {
return Long.parseLong(givenPath.substring(givenPath.lastIndexOf('/') + 1));
}
return null;
}
}
I keep getting a NullPointerException POSTing something to the API endpoint that is deserialized with the JsonDeserializer above.

Answer 1

I was able to solve a similar problem by marking my deserializer constructor accept a parameter (and therefore removing the empty constructor) and marking constructor as #Autowired.
public class MyDeserializer extends JsonDeserializer<MyEntity> {
private final MyBean bean;
// no default constructor
#Autowired
public MyDeserializer(MyBean bean){
this.bean = bean
}
...
}
#JsonDeserialize(using = MyDeserializer.class)
public class MyEntity{...}
My entity is marked with annotation #JsonDeserialize so I don't have to explicitly register it with ObjectMapper.