GWTP HTML5 pushState place manager implementation

Html5PushStatePlaceManager.java

package com.gwtplatform.mvp.client.proxy;

import com.google.gwt.event.logical.shared.ValueChangeEvent;
import com.google.gwt.user.client.Window;
import com.google.inject.Inject;
import com.google.inject.Singleton;
import com.google.web.bindery.event.shared.EventBus;

@Singleton
public class Html5PushStatePlaceManager extends PlaceManagerImpl {

    @Inject
    public Html5PushStatePlaceManager(
            final EventBus eventBus,
            final TokenFormatter tokenFormatter) {
        super(eventBus, tokenFormatter);
    }

    private String getGwtCodesvr() {
        return Window.Location.getParameter("gwt.codesvr");
    }

    @Override
    void setBrowserHistoryToken(String historyToken, boolean issueEvent) {
        // Need to ensure we don't accidentally leave development mode
        String path = historyToken;
        String gwtCodesvr = getGwtCodesvr();
        if (gwtCodesvr != null) {
            if (path.contains("?")) {
                path += "&";
            } else {
                path += "?";
            }
            path += "gwt.codesvr=" + gwtCodesvr;
        }
        pushState(path, historyToken);
    }

    /**
     * Push the state using HTML5 push state.  This method will fallback to doing a page refresh style load if HTML5
     * pushState is not available.
     *
     * @param path         The path to push
     * @param historyToken The history token to load if the back/forward buttons are used
     * @return True if pushState was available and it succeeded, otherwise false.
     */
    private native boolean pushState(String path, String historyToken) /*-{
        var state = {historyToken:historyToken};
        if ($wnd.history && $wnd.history.pushState) {
            var length = $wnd.history.length;
            $wnd.history.pushState(state, null, path);
            if (length != $wnd.history.length) {
                return true;
            } else {
                // If the history length hasn't changed, then pushState mustn't be enabled.  Fall back to $wnd.location.
                $wnd.location = path;
                return false;
            }
        } else {
            $wnd.location = path;
            return false;
        }
    }-*/;

    /**
     * Overridden so that it returns the path (and query string) rather than everything after the hash.
     *
     * @return The history token
     */
    @Override
    String getBrowserHistoryToken() {
        String historyToken = Window.Location.getPath();
        // Get the query string, but exclude the gwt.codesvr parameter if it exists
        String queryString = Window.Location.getQueryString();
        if (queryString != null) {
            queryString = queryString.replaceAll("gwt\\.codesvr=[^&]*", "");
            if (!queryString.trim().isEmpty() && !queryString.equals("?")) {
                historyToken += queryString;
            }
        }
        return historyToken;
    }

    /**
     * Overridden so that rather than registering a GWT history handler, registers an HTML5 popState handler.
     */
    @Override
    void registerTowardsHistory() {
        registerPopStateHandler();
    }

    /**
     * Register a handler for pop state.  If one already exists, it will be called after this one does its thing.
     */
    private native void registerPopStateHandler() /*-{
        var placeManager = this;

        var oldHandler = $wnd.onpopstate;

        $wnd.onpopstate = $entry(function (event) {
            if (event.state && event.state.historyToken) {
                placeManager.@com.gwtplatform.mvp.client.proxy.Html5PushStatePlaceManager::onPopState(Ljava/lang/String;)(event.state.historyToken);
            }

            if (oldHandler) {
                oldHandler(event);
            }
        });
    }-*/;

    /**
     * Called by native code when someone pushes the back/forward button.
     *
     * @param historyToken The history token that has been navigated to
     */
    void onPopState(String historyToken) {
        onValueChange(new ValueChangeEvent<String>(historyToken) {
        });
    }

    /**
     * Overridden so that it doesn't go through the GWT history stuff
     */
    @Override
    public void revealCurrentPlace() {
        onValueChange(new ValueChangeEvent<String>(getBrowserHistoryToken()) {
        });
    }
}