ResourceCache cache = (ResourceCache)wapp.getAttribute(ATTR_PAGE_CACHE);
if (cache == null) {
synchronized (PageDefinitions.class) {
cache = (ResourceCache)wapp.getAttribute(ATTR_PAGE_CACHE);
if (cache == null) {
Loader loader = null;
final String clsnm = Library.getProperty("org.zkoss.zk.ui.metainfo.page.Loader.class");
if (clsnm != null) {
try {
final Object o = Classes.newInstanceByThread(clsnm,
new Class[] {WebApp.class},