injecting ConversionService into a custom Converter

Question

Using Spring mvc-3. I am writing a custom Converter which needs access to other Converters registered to a ConversionService.

How can I accomplish this? I tried writing my custom converter as:

  class CustomConverter<X, Y>{
     @Autowired ConversionService service;
     //+getter & setters of service

     public Y convert(X input){
          // I need access to service to lookup simple conversions such as
          // String array to Long array etc..

     }

  }

And I registered my custom converter via applicationContext.xml

  <bean id="conversionService" class="org.springframework.context.support.ConversionServiceFactoryBean">
     <property name = "converters">
         <list>
            <bean class="CustomConverter"/>
         </list>
     </property>
  </bean>

However, spring refuses to inject service into my CustomConverter(its always null). How can I accomplish this?

Thank you!

Answer 1

I have come across same problem. There's an issue SPR-6415 in Spring JIRA covering this problem. I've giving here my solution based on discussion in this issue. It's the same principle like answer of @nmervaillie but you don't have to implement your own ConversionServiceFactoryBean.

/**
 * Base class of @{code Converter} that need to use {@code ConversionService}.
 * Instances of implementing classes must be spring-managed to inject ConversionService.
 * 
 * @author Michal Kreuzman
 */
public abstract class CoversionServiceAwareConverter<S, T> implements Converter<S, T> {

  @Inject
  private ConversionService conversionService;

  protected ConversionService conversionService() {
    return conversionService;
  }

  /**
   * Add this converter to {@code ConverterRegistry}.
   */
  @SuppressWarnings("unused")
  @PostConstruct
  private void register() {
    if (conversionService instanceof ConverterRegistry) {
      ((ConverterRegistry) conversionService).addConverter(this);
    } else {
      throw new IllegalStateException("Can't register Converter to ConverterRegistry");
    }
  }
}

@Component
public class SampleConverter extends CoversionServiceAwareConverter<Object, Object> {

    @Override
    public String convert(Object source) {
        ConversionService conversionService = conversionService();

        // Use conversionService and convert
    }
}