How to register Converter in Spring Data Rest application - spring

Question

I have Spring converter which uses Spring Data REST's component called EnumTranslator
#Component
public class TranslationStringToSpecificationStatusEnumConverter implements Converter<String, Specification.Status> {
private final EnumTranslator enumTranslator;
#Autowired
public TranslationStringToSpecificationStatusEnumConverter(EnumTranslator enumTranslator) {
this.enumTranslator = enumTranslator;
}
#Override
public Specification.Status convert(String source) {
return enumTranslator.fromText(Specification.Status.class, source);
}
}
Recommended way to register such converter is to subclass RepositoryRestConfigurerAdapter as follows:
#Configuration
public class RepositoryRestConfig extends RepositoryRestConfigurerAdapter {
private final TranslationStringToSpecificationStatusEnumConverter converter;
#Autowired
public RepositoryRestConfig(TranslationStringToSpecificationStatusEnumConverter converter) {
this.converter = converter;
}
#Override
public void configureConversionService(ConfigurableConversionService conversionService) {
conversionService.addConverter(converter);
super.configureConversionService(conversionService);
}
}
When I run the Spring Boot application, it fails on the following:
***************************
APPLICATION FAILED TO START
***************************
Description:
The dependencies of some of the beans in the application context form a cycle:
┌─────┐
| translationStringToSpecificationStatusEnumConverter defined in file ...
↑ ↓
| org.springframework.data.rest.webmvc.config.RepositoryRestMvcConfiguration (field java.util.List org.springframework.data.rest.webmvc.config.RepositoryRestMvcConfiguration.configurers)
↑ ↓
| repositoryRestConfig defined in file ...
└─────┘
So there is circular bean dependency.
How can I register the converter above so that I don't introduce circular bean dependency?

Answer 1

To make it work:
#Override
public void configureConversionService(ConfigurableConversionService conversionService) {
conversionService.addConverter(String.class, Status.class, new StringToTranslatedEnumConverter<>(Status.class));
super.configureConversionService(conversionService);
}
First I created utility class that help me work with Spring beans in unmanaged objects:
#Component
public final class SpringUtils {
#Autowired private ApplicationContext ctx;
private static SpringUtils instance;
#PostConstruct
private void registerInstance() {
instance = this;
}
public static <T> T getBean(Class<T> clazz) {
return instance.ctx.getBean(clazz);
}
}
Then I created the converter:
public class StringToTranslatedEnumConverter<T extends Enum<T> & TranslatedEnum> implements Converter<String, T> {
private final ConcurrentMapCache cache;
private EnumTranslator enumTranslator;
private Class<T> type;
public StringToTranslatedEnumConverter(Class<T> type) {
this.type = type;
cache = new ConcurrentMapCache(type.getName());
}
#Override
public T convert(String from) {
if (enumTranslator == null) {
enumTranslator = SpringUtils.getBean(EnumTranslator.class);
}
Cache.ValueWrapper wrapper = cache.get(from);
if (wrapper != null) {
//noinspection unchecked
return (T) wrapper.get();
}
T translatedEnum = enumTranslator.fromText(type, from);
cache.put(from, translatedEnum);
return translatedEnum;
}
}
UPDATED
TranslatedEnum - it's interface-marker, used to mark enums which translation is only need.
public interface TranslatedEnum {
}
public enum Status implements TranslatedEnum {
CREATED, DELETED
}

Answer 2

The solution to this problem is Spring Core specific. In order to break circle bean dependency cycle, we have to delay setting converter in RepositoryRestConfig. It can be achieved with setter injection:
#Component
public class RepositoryRestConfig extends RepositoryRestConfigurerAdapter {
private TranslationStringToSpecificationStatusEnumConverter converter;
#Override
public void configureConversionService(ConfigurableConversionService conversionService) {
conversionService.addConverter(converter);
super.configureConversionService(conversionService);
}
#Autowired
public void setConverter(TranslationStringToSpecificationStatusEnumConverter converter) {
this.converter = converter;
}
}
You can find how to solve it in this commit by Greg Turnquist: https://github.com/pmihalcin/custom-converter-in-spring-data-rest/commit/779a6477d76dc77515b3e923079e5a6543242da2