In Java - how do I get a full stack trace

问题

Currently I get the following output from code run

Caused by: java.lang.NullPointerException
    at com.gargoylesoftware.htmlunit.html.HtmlScript$2.execute(HtmlScript.java:227)
    at com.gargoylesoftware.htmlunit.html.HtmlScript.onAllChildrenAddedToPage(HtmlScript.java:256)
    at com.gargoylesoftware.htmlunit.html.parser.neko.HtmlUnitNekoDOMBuilder.endElement(HtmlUnitNekoDOMBuilder.java:560)
    at org.apache.xerces.parsers.AbstractSAXParser.endElement(Unknown Source)
    at com.gargoylesoftware.htmlunit.html.parser.neko.HtmlUnitNekoDOMBuilder.endElement(HtmlUnitNekoDOMBuilder.java:514)
    at net.sourceforge.htmlunit.cyberneko.HTMLTagBalancer.callEndElement(HTMLTagBalancer.java:1192)
    at net.sourceforge.htmlunit.cyberneko.HTMLTagBalancer.endElement(HTMLTagBalancer.java:1132)
    at net.sourceforge.htmlunit.cyberneko.filters.DefaultFilter.endElement(DefaultFilter.java:219)
    at net.sourceforge.htmlunit.cyberneko.filters.NamespaceBinder.endElement(NamespaceBinder.java:312)
    at net.sourceforge.htmlunit.cyberneko.HTMLScanner$ContentScanner.scanEndElement(HTMLScanner.java:3189)
    at net.sourceforge.htmlunit.cyberneko.HTMLScanner$ContentScanner.scan(HTMLScanner.java:2114)
    at net.sourceforge.htmlunit.cyberneko.HTMLScanner.scanDocument(HTMLScanner.java:937)
    at net.sourceforge.htmlunit.cyberneko.HTMLConfiguration.parse(HTMLConfiguration.java:443)
    at net.sourceforge.htmlunit.cyberneko.HTMLConfiguration.parse(HTMLConfiguration.java:394)
    at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
    at com.gargoylesoftware.htmlunit.html.parser.neko.HtmlUnitNekoDOMBuilder.parse(HtmlUnitNekoDOMBuilder.java:760)
    at com.gargoylesoftware.htmlunit.html.parser.neko.HtmlUnitNekoHtmlParser.parseFragment(HtmlUnitNekoHtmlParser.java:158)
    at com.gargoylesoftware.htmlunit.html.parser.neko.HtmlUnitNekoHtmlParser.parseFragment(HtmlUnitNekoHtmlParser.java:112)
    at com.gargoylesoftware.htmlunit.javascript.host.Element.parseHtmlSnippet(Element.java:868)
    at com.gargoylesoftware.htmlunit.javascript.host.Element.setInnerHTML(Element.java:920)
    at com.gargoylesoftware.htmlunit.javascript.host.html.HTMLElement.setInnerHTML(HTMLElement.java:676)
    at sun.reflect.GeneratedMethodAccessor17.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at net.sourceforge.htmlunit.corejs.javascript.MemberBox.invoke(MemberBox.java:188)
    ... 30 more

The above ... 30 more means that I do not know the line of my code that causes the problem. How can I get the full stack trace.

Also, if it does not seem to be running any of my catch statements with printStackTrace, but if I turn off logging with the below command

java.util.logging.Logger.getLogger("com.gargoylesoftware.htmlunit").setLevel(java.util.logging.Level.OFF);

java.util.logging.Logger.getLogger("org.apache.http").setLevel(java.util.logging.Level.OFF);


**Have put in my full code below as suggested by the comments below . Did not put in the actual URL though**

import com.gargoylesoftware.htmlunit.html.*;
import java.io.File;
import com.gargoylesoftware.htmlunit.WebClient;
import com.gargoylesoftware.htmlunit.html.HtmlPage;



public class download_to_send_to_stackoverflow
{
     public static void main(String args[])
     {

      String url = "did not want to include the actual web site ";


      HtmlPage page = null;

      WebClient webClient = new WebClient();
      webClient.getOptions().setRedirectEnabled(true);  
      webClient.getOptions().setJavaScriptEnabled(true);  // tried making false - but didnt work
      webClient.getOptions().setCssEnabled(false);
      webClient.getOptions().setUseInsecureSSL(true);
          webClient.getOptions().setTimeout(30000);
      webClient.setJavaScriptTimeout(30000); //e.g. 50s
      webClient.waitForBackgroundJavaScript(15000) ;   // added 2017/1/24
      webClient.waitForBackgroundJavaScriptStartingBefore(30000) ;   // added 2017/1/24


          try
               {
               page = webClient.getPage( url );
           savePage_just_html(page );  
           }

          catch( Exception e )
               {
               System.out.println( "Exception thrown:----------------------------------------" + e.getMessage() );
               e.printStackTrace();
               }
     }




     protected static String savePage_just_html(HtmlPage page)
     {
          try
          {
            File saveFolder = new File("spool/_");
            page.save(saveFolder);   // this is the line causing the error with limit stack trace
          }



          catch ( Exception e )
          {
               System.out.println( "IOException was thrown: ---------------------------------- " + e.getMessage() );
               e.printStackTrace();
          }


          return "file.html";
     }



}



------------------------------------------------------


  page.save(saveFolder);   above is the problem line.  if I take it out I dont get the limited statcktrace errors but I also dont save the html page - which I want to do

- The question is - why does this line only print a limited stacktrace

回答1:

The "Caused by" means that this is a nested exception.

The "... 30 more" in a nested exception stacktrace means that those 30 lines are the same as in the primary exception.

So just look at the primary stacktrace to see those stack frames.

---

Apparently your exception stacktraces are being generated in a way that is suppressing (or removing) the primary exception stacktrace. This is puzzling, but it is probably being done by one of the unit testing libraries that you are using.

Getting to the bottom of this will probably involve you either debugging whatever it is that is generating the stacktrace, or writing a minimal reproducible example so that someone else can debug it.

来源：https://stackoverflow.com/questions/63406604/in-java-how-do-i-get-a-full-stack-trace