为什么HtmlUnit中的WebClient消耗更多的执行时间？

Question

我使用HtmlUnit抓取网页内容（有javascript）

   Stopwatch timer = new Stopwatch().start();
   final WebClient webClient = new WebClient(BrowserVersion.CHROME);
   webClient.getOptions().setThrowExceptionOnFailingStatusCode(false);
   webClient.getOptions().setJavaScriptEnabled(true);
   webClient.getOptions().setActiveXNative(false);
   webClient.getOptions().setAppletEnabled(false);
   webClient.getOptions().setCssEnabled(false);
   webClient.getOptions().setDoNotTrackEnabled(true);
   webClient.getOptions().setGeolocationEnabled(false);
   webClient.getOptions().setPopupBlockerEnabled(true);
   webClient.getOptions().setPrintContentOnFailingStatusCode(false);
   webClient.getOptions().setThrowExceptionOnFailingStatusCode(false);
   webClient.getOptions().setThrowExceptionOnScriptError(false);
   webClient.getOptions().setUseInsecureSSL(true);
   webClient.setCssErrorHandler(new SilentCssErrorHandler());
   webClient.getCookieManager().setCookiesEnabled(false);
   webClient.getOptions().setRedirectEnabled(false);
   webClient.getOptions().setTimeout(900);

   System.out.println("1.0 : " + timer.elapsed(TimeUnit.MILLISECONDS));
   final HtmlPage page = webClient.getPage(url);
   System.out.println(page.getWebResponse().getLoadTime());
   System.out.println("1.1 : " + timer.elapsed(TimeUnit.MILLISECONDS));

然后我得到的结果是这样的

   1.0 : 2
   707
   1.1 : 8003

为什么webclient消耗更多时间（超过webresponse加载时间）？我怎样才能缩短那段时间？