Spring Data Rest - Null Pointer in PersistentEntityResourceAssembler - spring-mvc

Question

I have an issue with #RepositoryRestResource returning a 500 error due to a null pointer.
I have an abstract class named Resource which is uses InheritanceType.JOINED and #JsonSubTypes to provide about 5 subclasses of Resource such as ServerResource. The specific Resource is returned fine when referenced in another entity that it joins with. The PagingAndSortingRepository also works fine when called in code. The problem is the endpoint exposed by #RepositoryRestResource for the Resource entity returns a 500 error (due to NPE) when called directly.
After debugging, I found the issue is due to the line PersistentEntityResourceAssembler:154. The mapping object is null because the framework could not map ServerResource.class to the parent Resource.class. The cache is a map, and uses .getClass().
Are there any ways I can get one endpoint for the Resource entity working for these separate types? This almost seems like a bug.

Answer 1

To correct this issue i overrode the resourceMappings() method, and injected the mappings I needed. This fixed the issue, and now the /resources uri is working as intended.
package com.environment.config;
import java.lang.reflect.Field;
import java.util.Map;
import org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.type.filter.AssignableTypeFilter;
import org.springframework.data.rest.core.config.RepositoryRestConfiguration;
import org.springframework.data.rest.core.mapping.RepositoryResourceMappings;
import org.springframework.data.rest.core.mapping.ResourceMappings;
import org.springframework.data.rest.core.mapping.ResourceMetadata;
import org.springframework.data.rest.webmvc.config.RepositoryRestMvcConfiguration;
import com.environment.domain.Resource;
import com.environment.util.Tuple;
#Configuration
public class RepositoryConfig extends RepositoryRestMvcConfiguration {
#Override
public ResourceMappings resourceMappings() {
RepositoryResourceMappings rm = RepositoryResourceMappings)super.resourceMappings();
try {
Field cacheField = rm.getClass().getDeclaredField("cache");
cacheField.setAccessible(true);
Map<Class<?>, ResourceMetadata> cache = (Map<Class<?>, ResourceMetadata>) cacheField.get(rm);
//Get metadata for parent object
ResourceMetadata resourceMetadata = cache.entrySet().stream()
.map(Tuple<Class<?>,ResourceMetadata>::new)
.filter(t -> Resource.class.equals(t.t))
.map(t -> t.u)
.findFirst()
.get();
ClassPathScanningCandidateComponentProvider provider = new ClassPathScanningCandidateComponentProvider(false);
provider.addIncludeFilter(new AssignableTypeFilter(Resource.class));
provider.findCandidateComponents("com/environment")
.stream()
.map(beanDef -> {
try {
return Class.forName(beanDef.getBeanClassName());
} catch (Exception e) {
e.printStackTrace();
}
return null;
})
.filter(c -> !Resource.class.equals(c))
.filter(c -> Resource.class.isAssignableFrom(c))
.peek(c -> System.out.println("Mapping: " + c)
.forEach(c -> cache.put((Class<?>) c, resourceMetadata));
} catch (Exception e) {
e.printStackTrace();
}
return rm;
}
}