Inject Service into custom Jackson Serializer

问题

Hi I have problem in the following scenario:

I'm using Spring 4.xx with Jackson 2.xx and I'm ompelenting a RESTful Web Application. I'm now faced with te problem that I need some custom serialzation for one of my models, so i used a custom serilaizer, but i also need to fetch some data out of the database while serializing. So I tried to inject my Serivce into the Serializer but it always stays null.

As far as I have read this happens if you instanciate your object directly, which I guess is what Jackson does. But is there any way to still use Dependency Injection?

Also if I make the class implement the ApplicationContextAware interface and call ApplicationContext#getBean() it hangs forever.

Here is some code to illustrate my problem

Serialzer.java

public class TheSerializer extends JsonSerializer<MyObject>
  implements ApplicationContextAware {

  @Autowired
  ITheService theService;

  ApplicationContext ctx;

  public vodi serialize(MyObject o, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
    if(theService == null) {
      theService = ctx.getBean(ITheService.class); //This is where it hangs
      //If I don't do this I get a NPE if I try to use theSerivice
    }
  }
}

My configuration is mainly annotaion based, only the databse stuff is done in xml.

Thank you in advance,

wastl

回答1:

You can use @Configurable spring annotation to inject spring bean into the non spring beans.

Some explanation how to do it: http://www.kubrynski.com/2013/09/injecting-spring-dependencies-into-non.html

回答2:

The Jackson ObjectMapper allows you to inject a HandlerInstantiator, which it will use to create JsonSerializers and JsonDeserializers (among other things).

In v4.1.3, Spring introduced a SpringHandlerInstantiator, which implements this interface, and does all the autowiring for you.

So, all you need is configure your ObjectMapper:

@Bean
public SpringHandlerInstantiator handlerInstantiator(AutowireCapableBeanFactory beanFactory)
{
    return new SpringHandlerInstantiator(beanFactory);
}

@Bean
public ObjectMapper objectMapper(SpringHandlerInstantiator handlerInstantiator)
{
    ObjectMapper mapper = new ObjectMapper();
    mapper.setHandlerInstantiator(handlerInstantiator);
    return mapper;
}

You can also set this property on a Jackson2ObjectMapperBuilder, if you're creating your ObjectMapper that way.

来源：https://stackoverflow.com/questions/27369842/inject-service-into-custom-jackson-serializer

标签

java

Spring

serialization

dependency-injection

jackson