How to Autowired in ConversionService in springboot

Question

Trying to access the ConversionControl in model in springboot, no luck.

@Component
public class CityHelperService  {

    @Autowired
    ConversionService conversionService;// = ConversionServiceFactory.registerConverters();

    public City toEntity(CityDTO dto){
        City entity = conversionService.convert(dto, City.class);
        return entity;
    }

    public CityDTO toDTO(City entity){
        CityDTO dto = conversionService.convert(entity, CityDTO.class);
        return dto;
    }
}

It shows the following error:

Injection of autowired dependencies failed;
nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.lumiin.mytalk.model.CityModel com.lumiin.mytalk.controllers.CityController.cityModel;
nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'cityModel' defined in file : Unsatisfied dependency expressed through constructor argument with index 1 of type [com.lumiin.mytalk.dao.CityHelperService]: : Error creating bean with name 'cityHelperService': Injection of autowired dependencies failed;
nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: org.springframework.core.convert.ConversionService com.lumiin.mytalk.dao.CityHelperService.conversionService;
nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [org.springframework.core.convert.ConversionService] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)};
nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'cityHelperService': Injection of autowired dependencies failed;
nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: org.springframework.core.convert.ConversionService com.lumiin.mytalk.dao.CityHelperService.conversionService;
nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [org.springframework.core.convert.ConversionService] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

Answer 1

Apparently there is no ConversionService bean available, judging by the last nested exception:

org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [org.springframework.core.convert.ConversionService] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency.

A look into the Spring documentation reveals, that you should declare a ConversionService bean. In the XML configuration it would look like this:

<bean id="conversionService" class="org.springframework.context.support.ConversionServiceFactoryBean">
    <property name="converters">
        <set>
            <bean class="example.MyCustomConverter"/>
        </set>
    </property>
</bean>

And since you're using Spring Boot, I assume you are creating the context programatically, so you should create a method annotated with @Bean, which returns a ConverstionService, like this (explained here):

@Bean(name="conversionService")
public ConversionService getConversionService() {
    ConversionServiceFactoryBean bean = new ConversionServiceFactoryBean();
    bean.setConverters(...); //add converters
    bean.afterPropertiesSet();
    return bean.getObject();
}