Why do I have java.util.EmptyStackException when using HTMLUnit to render the page via Filter?

[Tom]

Ok, I have a Filter

public class CrawlServlet implements Filter{
   @Override
   public void doFilter(ServletRequest request, ServletResponse response,
        FilterChain chain) throws IOException, ServletException {
      HttpServletRequest httpRequest = (HttpServletRequest) request;
      String requestQueryString = httpRequest.getQueryString();
      if ((requestQueryString != null) && (requestQueryString.contains("_escaped_fragment_"))) {
           String str="http://127.0.0.1:8888/Myproject.html?gwt.codesvr=127.0.0.1:9997#!article";
           // this url work fine, if i open it it will show article.
           final WebClient webClient = new WebClient();
           HtmlPage page = webClient.getPage(str);
           PrintWriter out = response.getWriter();
           out.println(page.asXml());
      }

   }
}

Ok, now i ran my app in eclipse, & open the url http://127.0.0.1:8888/Myproject.html?gwt.codesvr=127.0.0.1:9997?_escaped_fragment_=article

Then I got this error in eclipse

    .GWTUpld .gwt-Button:HOVER,
.GWTUpld .DecoratedFileUpload .gwt-Button-over,
.GWTUpld .DecoratedFileUpload .gwt-Anchor-over,
.GWTUpld .DecoratedFileUpload .gwt-Label-over {
    color: #af6b29;
}
......
.GWTUpld input[type="file"] {
    cursor: pointer;
}


': null
java.util.EmptyStackException
    at java.util.Stack.peek(Unknown Source)
    at java.util.Stack.pop(Unknown Source)
    at com.steadystate.css.parser.CSSOMParser$CSSOMHandler.endDocument(CSSOMParser.java:271)
    at com.steadystate.css.parser.AbstractSACParser.handleEndDocument(AbstractSACParser.java:456)
    at com.steadystate.css.parser.SACParserCSS3.styleSheet(SACParserCSS3.java:56)
    at com.steadystate.css.parser.AbstractSACParser.parseStyleSheet(AbstractSACParser.java:284)
    at com.steadystate.css.parser.SACParserCSS3.parseStyleSheet(SACParserCSS3.java:23)
    at com.steadystate.css.parser.CSSOMParser.parseStyleSheet(CSSOMParser.java:146)
    at com.gargoylesoftware.htmlunit.javascript.host.css.CSSStyleSheet.parseCSS(CSSStyleSheet.java:818)
    at com.gargoylesoftware.htmlunit.javascript.host.css.CSSStyleSheet.(CSSStyleSheet.java:179)
    at com.gargoylesoftware.htmlunit.javascript.host.css.CSSStyleSheet.loadStylesheet(CSSStyleSheet.java:321)
    at com.gargoylesoftware.htmlunit.javascript.host.html.HTMLLinkElement.getSheet(HTMLLinkElement.java:130)
    at com.gargoylesoftware.htmlunit.javascript.host.css.StyleSheetList.item(StyleSheetList.java:151)
    at com.gargoylesoftware.htmlunit.javascript.host.Window.getComputedStyle(Window.java:1601)
    at com.gargoylesoftware.htmlunit.javascript.host.Element.getCurrentStyle(Element.java:545)
    at com.gargoylesoftware.htmlunit.html.DomNode.isDisplayed(DomNode.java:712)
    at com.gargoylesoftware.htmlunit.WebClient$CurrentWindowTracker.webWindowContentChanged(WebClient.java:1671)
    at com.gargoylesoftware.htmlunit.WebClient.fireWindowContentChanged(WebClient.java:742)
    at com.gargoylesoftware.htmlunit.WebClient.loadWebResponseInto(WebClient.java:440)
    at com.gargoylesoftware.htmlunit.WebClient.loadDownloadedResponses(WebClient.java:2024)
    at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine.doProcessPostponedActions(JavaScriptEngine.java:712)
    at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine.access$500(JavaScriptEngine.java:92)
    at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine$HtmlUnitContextAction.run(JavaScriptEngine.java:679)
    at net.sourceforge.htmlunit.corejs.javascript.Context.call(Context.java:602)
    at net.sourceforge.htmlunit.corejs.javascript.ContextFactory.call(ContextFactory.java:507)
    at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine.callFunction(JavaScriptEngine.java:616)
    at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine.callFunction(JavaScriptEngine.java:591)
    at com.gargoylesoftware.htmlunit.html.HtmlPage.executeJavaScriptFunctionIfPossible(HtmlPage.java:985)
    at com.gargoylesoftware.htmlunit.javascript.background.JavaScriptFunctionJob.runJavaScript(JavaScriptFunctionJob.java:53)
    at com.gargoylesoftware.htmlunit.javascript.background.JavaScriptExecutionJob.run(JavaScriptExecutionJob.java:102)
    at com.gargoylesoftware.htmlunit.javascript.background.JavaScriptJobManagerImpl.runSingleJob(JavaScriptJobManagerImpl.java:328)
    at com.gargoylesoftware.htmlunit.javascript.background.DefaultJavaScriptExecutor.run(DefaultJavaScriptExecutor.java:162)
    at java.lang.Thread.run(Unknown Source)

May 16, 2014 1:36:41 PM com.gargoylesoftware.htmlunit.javascript.host.css.CSSStyleSheet parseCSS
SEVERE: Error parsing CSS from '/**
* The file contains styles for GWT widgets in the standard theme.
 *
 * In order to maintain cross-browser compatibility, the following syntax is
 * used to create IE6 specific style rules:
 *    .gwt-Widget {
 *      property: rule applies to all browsers
 *      -property: rule applies only to IE6 (overrides previous rule)
 *    }
 *    * html .gwt-Widget {
 *      property: rule applies to all versions of IE
 *    }
 */
.......
': null
java.util.EmptyStackException
    at java.util.Stack.peek(Unknown Source)
    at java.util.Stack.pop(Unknown Source)
    at com.steadystate.css.parser.CSSOMParser$CSSOMHandler.endDocument(CSSOMParser.java:271)
    at com.steadystate.css.parser.AbstractSACParser.handleEndDocument(AbstractSACParser.java:456)
    at com.steadystate.css.parser.SACParserCSS3.styleSheet(SACParserCSS3.java:56)
    at com.steadystate.css.parser.AbstractSACParser.parseStyleSheet(AbstractSACParser.java:284)
    at com.steadystate.css.parser.SACParserCSS3.parseStyleSheet(SACParserCSS3.java:23)
    at com.steadystate.css.parser.CSSOMParser.parseStyleSheet(CSSOMParser.java:146)
    at com.gargoylesoftware.htmlunit.javascript.host.css.CSSStyleSheet.parseCSS(CSSStyleSheet.java:818)
    at com.gargoylesoftware.htmlunit.javascript.host.css.CSSStyleSheet.(CSSStyleSheet.java:179)
    at com.gargoylesoftware.htmlunit.javascript.host.css.CSSStyleSheet.loadStylesheet(CSSStyleSheet.java:321)
    at com.gargoylesoftware.htmlunit.javascript.host.html.HTMLLinkElement.getSheet(HTMLLinkElement.java:130)
    at com.gargoylesoftware.htmlunit.javascript.host.css.StyleSheetList.item(StyleSheetList.java:151)
    at com.gargoylesoftware.htmlunit.javascript.host.Window.getComputedStyle(Window.java:1601)
    at com.gargoylesoftware.htmlunit.javascript.host.Element.getCurrentStyle(Element.java:545)
    at com.gargoylesoftware.htmlunit.html.DomNode.isDisplayed(DomNode.java:712)
    at com.gargoylesoftware.htmlunit.WebClient$CurrentWindowTracker.webWindowContentChanged(WebClient.java:1671)
    at com.gargoylesoftware.htmlunit.WebClient.fireWindowContentChanged(WebClient.java:742)
    at com.gargoylesoftware.htmlunit.WebClient.loadWebResponseInto(WebClient.java:440)
    at com.gargoylesoftware.htmlunit.WebClient.loadDownloadedResponses(WebClient.java:2024)
    at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine.doProcessPostponedActions(JavaScriptEngine.java:712)
    at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine.access$500(JavaScriptEngine.java:92)
    at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine$HtmlUnitContextAction.run(JavaScriptEngine.java:679)
    at net.sourceforge.htmlunit.corejs.javascript.Context.call(Context.java:602)
    at net.sourceforge.htmlunit.corejs.javascript.ContextFactory.call(ContextFactory.java:507)
    at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine.callFunction(JavaScriptEngine.java:616)
    at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine.callFunction(JavaScriptEngine.java:591)
    at com.gargoylesoftware.htmlunit.html.HtmlPage.executeJavaScriptFunctionIfPossible(HtmlPage.java:985)
    at com.gargoylesoftware.htmlunit.javascript.background.JavaScriptFunctionJob.runJavaScript(JavaScriptFunctionJob.java:53)
    at com.gargoylesoftware.htmlunit.javascript.background.JavaScriptExecutionJob.run(JavaScriptExecutionJob.java:102)
    at com.gargoylesoftware.htmlunit.javascript.background.JavaScriptJobManagerImpl.runSingleJob(JavaScriptJobManagerImpl.java:328)
    at com.gargoylesoftware.htmlunit.javascript.background.DefaultJavaScriptExecutor.run(DefaultJavaScriptExecutor.java:162)
    at java.lang.Thread.run(Unknown Source)

Is this cos I have /*** ***/ comment line in css & that is why the HtmlUnit could not parse?

Can you fix this issue?

Also, How can we make sure HTMLUnit will work OK in all kind of html code?

Note: I am using htmlunit-2.14

[Tom]

i found this link

http://htmlunit.10904.n7.nabble.com/htmlunit-Bugs-1728761-java-util-EmptyStackException-in-webclient-td4900.html

Maybe this causing the problem:

!stack.empy() && stack.peek() .. stack.peek() is the one throwing this 
exception. May be that, when the current thread has checked !empty(), 
another thread has already consumed the data due to JVM memory model. May 
be we need to do in sych?? 

Do you think so, if it is the problem, then how to fix it.

[Tom]

It seems that after opened the url http://127.0.0.1:8888/Myproject.html?gwt.codesvr=127.0.0.1:9997?_escaped_fragment_=article, I can see the Chrome browser show the raw html page like this

This XML file does not appear to have any style information associated with it. The document tree is shown below.

<html>

..

<iframe src="javascript:''" id="ekajati" style="position:absolute;width:0;height:0;border:none" tabindex="-1"></iframe>

</body>

</html>

Buit that is the html code of the homepage (http://127.0.0.1:8888/Myproject.html?gwt.codesvr=127.0.0.1:9997#!home) while I opened the article page (http://127.0.0.1:8888/Myproject.html?gwt.codesvr=127.0.0.1:9997#!article)

This means that the HtmlUnit works but somehow it couldn't parse the article page.

WHy does that happen?