workaround for `java.lang.SecurityException: Prohibited package name` on regex Pattern

java.util.regex.Pattern has a method Map<String, Integer> namedGroups(). For some reason they decided to make it private, and so there is no way to obtain this very useful information! :(

I've tried accessing this information (read-only) with this helper class:

package java.util.regex;

import java.util.Collections;
import java.util.Map;

public class PatternHelper {
    public static Map<String, Integer> getNamedGroups(Pattern pattern) {
        return Collections.unmodifiableMap(pattern.namedGroups());
    }
}

But Java8 complains with java.lang.SecurityException: Prohibited package name: java.util.regex.

How can I access this information (read-only)? maybe by reflection?