Hamcrest matcher for asserting that a Wicket page is stateless

StatelessPageMatcher.java

package com.github.bjpbakker.gist;

import org.apache.wicket.Component;
import org.apache.wicket.Page;
import org.apache.wicket.util.visit.IVisit;
import org.apache.wicket.util.visit.IVisitor;
import org.hamcrest.Description;
import org.hamcrest.Matcher;
import org.hamcrest.TypeSafeDiagnosingMatcher;

/**
 * Matches a page if it is stateless. Diagnoses if it is stateful.
 */
public class StatelessPageMatcher extends TypeSafeDiagnosingMatcher<Page> {
    public static Matcher<Page> stateless() {
        return new StatelessPageMatcher();
    }

    @Override
    protected boolean matchesSafely(Page page, Description mismatchDescription) {
        if (!page.isStateless()) {
            mismatchDescription.appendText("page is stateful");
        } else if (!page.isPageStateless()) {
            Component stateful = page.visitChildren(Component.class, new Stateful());
            if (stateful == null) {
                mismatchDescription.appendText("found stateful page; stateful child is unknown, it must be hidden or disabled");
            } else {
                mismatchDescription.appendText("found stateful child ").appendValue(stateful.getId());
            }
        }
        return page.isPageStateless();
    }

    @Override
    public void describeTo(Description description) {
        description.appendText("stateless");
    }

    private static class Stateful implements IVisitor<Component, Component> {
        @Override
        public void component(Component c, IVisit<Component> visit) {
            if (!c.isStateless()) {
                visit.stop(c);
            }
        }
    }
}

hi,
how can you extend JDBCAppender is it's final, and its constructor is private?