spring data jpa - Custom type conversion in interface-based projection

Question

I'm trying to implement Interface-based Projection but I cannot make it work with my custom type column.

Below example of what I'm trying to do:

Repository:

@Query(value = "SELECT customType from TABLE", nativeQuery = true)
List<TestClass> getResults();

Interface projection:

public interface TestClass {
  @Convert(converter = MyCustomTypeConverter.class)
  MyCustomType getCustomType();
}

Converter:

@Converter
public class MyCustomTypeConverter implements Converter<String, MyCustomType> {

      @Override
      public MyCustomType convert(String source) {
        // whatever
      }
}

When I call getResults() on repository I receive list of results as expected, but when I try to call getCustomType() on one of results I get exception:

java.lang.IllegalArgumentException: Projection type must be an interface!
at org.springframework.util.Assert.isTrue(Assert.java:118)
at org.springframework.data.projection.ProxyProjectionFactory.createProjection(ProxyProjectionFactory.java:100)
at org.springframework.data.projection.SpelAwareProxyProjectionFactory.createProjection(SpelAwareProxyProjectionFactory.java:45)
at org.springframework.data.projection.ProjectingMethodInterceptor.getProjection(ProjectingMethodInterceptor.java:131)
at org.springframework.data.projection.ProjectingMethodInterceptor.invoke(ProjectingMethodInterceptor.java:80)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
at org.springframework.data.projection.ProxyProjectionFactory$TargetAwareMethodInterceptor.invoke(ProxyProjectionFactory.java:245)

I found that problem lies in

org.springframework.data.projection.ProxyProjectionFactory

which uses

org.springframework.core.convert.support.DefaultConversionService

which obviously doesn't have my custom type converter registered.

If I stop on breakpoint in ConversionService and manually add my converter in runtime, projection will work without any problem.

So question is: can I somehow register my custom converter to ConversionService used by spring jpa during interface-based projection?

EDIT:

I added my converter to DefaultConversionService's sharedInstance in InitializingBean like below and it worked.

@Component
public class DefaultConversionServiceInitializer implements InitializingBean {

    @Override
    public void afterPropertiesSet() {
        DefaultConversionService conversionService = (DefaultConversionService) DefaultConversionService.getSharedInstance();
        conversionService.addConverter(new MyCustomTypeConverter());
    }
}

Answer 1

The ConversionService used is DefaultConversionService.getSharedInstance().

So you should be able to access that and add your converter.