import org.springframework.aop.RawTargetAccess; //导入依赖的package包/类
/**
 * Process a return value. Wraps a return of {@code this} if necessary to be the
 * {@code proxy} and also verifies that {@code null} is not returned as a primitive.
 */
private static Object processReturnType(Object proxy, Object target, Method method, Object retVal) {
	// Massage return value if necessary
	if (retVal != null && retVal == target && !RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
		// Special case: it returned "this". Note that we can't help
		// if the target sets a reference to itself in another returned object.
		retVal = proxy;
	}
	Class<?> returnType = method.getReturnType();
	if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
		throw new AopInvocationException(
				"Null return value from advice does not match primitive return type for: " + method);
	}
	return retVal;
}