config/src/main/java/org/springframework/security/config/annotation/web/builders/FilterComparator.java
public void registerAt(Class<? extends Filter> filter,
			Class<? extends Filter> atFilter) {
		Integer position = getOrder(atFilter);
		if (position == null) {
			throw new IllegalArgumentException(
					"Cannot register after unregistered Filter " + atFilter);
		}

		put(filter, position);
	}
public void registerAt(Class<? extends Filter> filter,
			Class<? extends Filter> atFilter) {
		Integer position = getOrder(atFilter);
		if (position == null) {
			throw new IllegalArgumentException(
					"Cannot register after unregistered Filter " + atFilter);
		}

		put(filter, position);
	}
Registers a {@link Filter} to exist at a particular {@link Filter} position
@param filter the {@link Filter} to register
@param atFilter the {@link Filter} that is already registered and that
{@code filter} should be placed at.