A Variant of the AuthenticationPrincipalArgumentResolver which injects an AuthenticationPrincipal merged into the correct EntityManager

AnnotationUtil.java

package net.seibertmedia.team-rocket.someproject.configuration.mergedAuthenticationPrincipal;

import java.lang.annotation.Annotation;

import org.springframework.core.MethodParameter;
import org.springframework.core.annotation.AnnotationUtils;

public class AnnotationUtil {
	private AnnotationUtil() {
	}

	/**
	 * Obtains the specified {@link Annotation} on the specified {@link MethodParameter}.
	 *
	 * @param annotationClass the class of the {@link Annotation} to find on the
	 *                        {@link MethodParameter}
	 * @param parameter       the {@link MethodParameter} to search for an {@link Annotation}
	 * @return the {@link Annotation} that was found or null.
	 */
	public static <T extends Annotation> T findMethodAnnotation(Class<T> annotationClass,
																MethodParameter parameter) {
		T annotation = parameter.getParameterAnnotation(annotationClass);
		if (annotation != null) {
			return annotation;
		}
		Annotation[] annotationsToSearch = parameter.getParameterAnnotations();
		for (Annotation toSearch : annotationsToSearch) {
			annotation = AnnotationUtils.findAnnotation(toSearch.annotationType(),
				annotationClass);
			if (annotation != null) {
				return annotation;
			}
		}
		return null;
	}
}

MergedAuthenticationPrincipalArgumentResolver.java

package net.seibertmedia.team-rocket.someproject.configuration.mergedAuthenticationPrincipal;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.MethodParameter;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.annotation.AuthenticationPrincipal;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;

import net.seibertmedia.team-rocket.someproject.model.security.User;
import net.seibertmedia.team-rocket.someproject.model.security.UserRepository;
import net.seibertmedia.team-rocket.someproject.security.SomeProjectNotAuthenticatedException;

@Component
public class MergedAuthenticationPrincipalArgumentResolver implements HandlerMethodArgumentResolver {

	@Autowired
	private UserRepository userRepository;

	public Object resolveArgument(
		MethodParameter parameter,
		ModelAndViewContainer mavContainer, NativeWebRequest webRequest,
		WebDataBinderFactory binderFactory
	) throws Exception {
		Authentication authentication = SecurityContextHolder.getContext().getAuthentication();

		if (authentication == null) {
			return null;
		}

		User principal = (User) authentication.getPrincipal();

		AuthenticationPrincipal authPrincipal = AnnotationUtil.findMethodAnnotation(AuthenticationPrincipal.class, parameter);

		if (principal == null) {
			throw new SomeProjectNotAuthenticatedException();
		}

		if (!parameter.getParameterType().isAssignableFrom(principal.getClass())) {
			throw new ClassCastException(principal + " is not assignable to " + parameter.getParameterType());
		}

		return userRepository.findById(principal.getId())
			.orElseThrow(SomeProjectNotAuthenticatedException::new);
	}

	/*
	 * (non-Javadoc)
	 *
	 * @see org.springframework.web.method.support.HandlerMethodArgumentResolver#
	 * supportsParameter (org.springframework.core.MethodParameter)
	 */
	public boolean supportsParameter(MethodParameter parameter) {
		return AnnotationUtil.findMethodAnnotation(AuthenticationPrincipal.class, parameter) != null;
	}
}

MergedAuthenticationPrincipalArgumentResolverConfigurer.java

package net.seibertmedia.team-rocket.someproject.configuration.mergedAuthenticationPrincipal;

import java.util.List;

import javax.persistence.EntityManagerFactory;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class MergedAuthenticationPrincipalArgumentResolverConfigurer implements WebMvcConfigurer {

	@Autowired
	private EntityManagerFactory entityManagerFactory;

	@Override
	public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
		argumentResolvers.add(0, new MergedAuthenticationPrincipalArgumentResolver(entityManagerFactory));
	}
}