BreadcrumbTrailExtendingListener.java

package lt.inventi.wicket.component.breadcrumb;

import static lt.inventi.wicket.component.breadcrumb.BreadcrumbPageParameters.getOptionalTrailId;

import org.apache.wicket.Component;
import org.apache.wicket.Page;
import org.apache.wicket.Session;
import org.apache.wicket.application.IComponentInitializationListener;
import org.apache.wicket.application.IComponentInstantiationListener;
import org.apache.wicket.application.IComponentOnBeforeRenderListener;
import org.apache.wicket.request.component.IRequestablePage;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

class BreadcrumbTrailExtendingListener implements IComponentOnBeforeRenderListener {
    /**
     * We cannot use {@link IComponentInitializationListener} or
     * {@link IComponentInstantiationListener} because navigation to the
     * breadcrumbs in the trail won't always create/initialize pages (in case
     * they're stateful and still in the page store). We construct unique trail
     * ids based on the page's hashCode and a deserialized page's hashCode
     * doesn't have to match the hashCode of the serialized one, thus we cannot
     * reliably find the previous page trail without extending it on each
     * render.
     * <p>
     * Possible improvement: store the newly created breadcrumb in the session's
     * metadata and use it in all further next page links. This way we can use
     * stable breadcrumb ids (page id + page class) and avoid creating new
     * breadcrumbs when the same page is rerendered (same page id + class but
     * different page object and thus hashCode).
     */
    private static final Logger logger = LoggerFactory.getLogger(BreadcrumbTrailExtendingListener.class);

    private final IBreadcrumbPageFilter pageFilter;
    private final IComponentBreadcrumbTitleProvider titleProvider;

    public BreadcrumbTrailExtendingListener(IBreadcrumbPageFilter pageFilter, IComponentBreadcrumbTitleProvider titleProvider) {
        this.pageFilter = pageFilter;
        this.titleProvider = titleProvider;
    }

    @Override
    public void onBeforeRender(Component component) {
        if (component instanceof Page) {
            if (pageFilter.shouldCreateBreadcrumbFor((IRequestablePage) component)) {
                Page p = (Page) component;
                Breadcrumb crumb = createBreadcrumbFrom(p);
                String maybeTrailId = getOptionalTrailId(p.getPageParameters());
                BreadcrumbTrailHistory.extendTrail(maybeTrailId, crumb);

                if (logger.isTraceEnabled()) {
                    logger.trace("Extended breadcrumb trail for trail {} with crumb {}", maybeTrailId, crumb);
                    logger.trace("Session size after extending trail: " + Session.get().getSizeInBytes() + " bytes");
                }
            } else {
                if (logger.isTraceEnabled()) {
                    logger.trace("Skipping breadcrumb trail extension for page: " + component);
                }
            }
        }
    }

    private Breadcrumb createBreadcrumbFrom(Page p) {
        return new Breadcrumb(p, titleProvider.getBreadcrumbTitle(p));
    }

}