java - 无法在我的代码中获取导致错误的实际行
问题描述
使用下面的示例代码，我得到了大量的堆栈跟踪错误，我知道这些错误来自page.save(saveFolder)行 - 但在错误中没有任何地方将此行作为错误。因此，当您的代码是 10 倍时 - 很难知道错误在哪里。
import com.gargoylesoftware.htmlunit.html.*;
import java.io.File;
import java.io.*;
import com.gargoylesoftware.htmlunit.WebClient;
public class download_to_send_to_stackoverflow {
public static void main(String args[]) {
System.out.println("Hello world!");
String url = "https://dont want to put actual web site down here";
HtmlPage page = null;
WebClient webClient = new WebClient();
webClient.getOptions().setRedirectEnabled(true);
webClient.getOptions().setJavaScriptEnabled(true);
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 );
File saveFolder = new File("spool/_");
page.save(saveFolder); // this is the line that is causing the error.
} catch( Exception e ) {
}
}
}
错误行如下： -
Aug 19, 2020 10:28:28 AM com.gargoylesoftware.htmlunit.javascript.DefaultJavaScriptErrorListener scriptException
SEVERE: Error during JavaScript execution
======= EXCEPTION START ========
Exception class=[java.lang.RuntimeException]
com.gargoylesoftware.htmlunit.ScriptException: Exception invoking setInnerHTML
at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine$HtmlUnitContextAction.run(JavaScriptEngine.java:929)
at net.sourceforge.htmlunit.corejs.javascript.Context.call(Context.java:619)
at net.sourceforge.htmlunit.corejs.javascript.ContextFactory.call(ContextFactory.java:537)
at com.gargoylesoftware.htmlunit.javascript.HtmlUnitContextFactory.callSecured(HtmlUnitContextFactory.java:354)
at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine.callFunction(JavaScriptEngine.java:858)
at com.gargoylesoftware.htmlunit.javascript.host.xml.XMLHttpRequest.setState(XMLHttpRequest.java:213)
at com.gargoylesoftware.htmlunit.javascript.host.xml.XMLHttpRequest.doSend(XMLHttpRequest.java:804)
at com.gargoylesoftware.htmlunit.javascript.host.xml.XMLHttpRequest.access$000(XMLHttpRequest.java:105)
at com.gargoylesoftware.htmlunit.javascript.host.xml.XMLHttpRequest$1.run(XMLHttpRequest.java:636)
at net.sourceforge.htmlunit.corejs.javascript.Context.call(Context.java:619)
at net.sourceforge.htmlunit.corejs.javascript.ContextFactory.call(ContextFactory.java:537)
at com.gargoylesoftware.htmlunit.javascript.background.JavascriptXMLHttpRequestJob.run(JavascriptXMLHttpRequestJob.java:36)
at com.gargoylesoftware.htmlunit.javascript.background.JavaScriptJobManagerImpl.runSingleJob(JavaScriptJobManagerImpl.java:429)
at com.gargoylesoftware.htmlunit.javascript.background.DefaultJavaScriptExecutor.run(DefaultJavaScriptExecutor.java:148)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.RuntimeException: Exception invoking setInnerHTML
at net.sourceforge.htmlunit.corejs.javascript.MemberBox.invoke(MemberBox.java:214)
at net.sourceforge.htmlunit.corejs.javascript.ScriptableObject$GetterSlot.setValue(ScriptableObject.java:323)
at net.sourceforge.htmlunit.corejs.javascript.ScriptableObject.putImpl(ScriptableObject.java:2868)
at net.sourceforge.htmlunit.corejs.javascript.ScriptableObject.put(ScriptableObject.java:536)
at com.gargoylesoftware.htmlunit.javascript.HtmlUnitScriptable.put(HtmlUnitScriptable.java:151)
at net.sourceforge.htmlunit.corejs.javascript.ScriptableObject.putProperty(ScriptableObject.java:2539)
at net.sourceforge.htmlunit.corejs.javascript.ScriptRuntime.setObjectElem(ScriptRuntime.java:1721)
at net.sourceforge.htmlunit.corejs.javascript.ScriptRuntime.setObjectElem(ScriptRuntime.java:1706)
at net.sourceforge.htmlunit.corejs.javascript.Interpreter.doSetElem(Interpreter.java:2460)
at net.sourceforge.htmlunit.corejs.javascript.Interpreter.interpretLoop(Interpreter.java:1488)
at net.sourceforge.htmlunit.corejs.javascript.Interpreter.interpret(Interpreter.java:1013)
at net.sourceforge.htmlunit.corejs.javascript.InterpretedFunction.call(InterpretedFunction.java:111)
at net.sourceforge.htmlunit.corejs.javascript.ContextFactory.doTopCall(ContextFactory.java:427)
at com.gargoylesoftware.htmlunit.javascript.HtmlUnitContextFactory.doTopCall(HtmlUnitContextFactory.java:340)
at net.sourceforge.htmlunit.corejs.javascript.ScriptRuntime.doTopCall(ScriptRuntime.java:3640)
at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine$3.doRun(JavaScriptEngine.java:851)
at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine$HtmlUnitContextAction.run(JavaScriptEngine.java:914)
... 14 more
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$ContentScanner.scan(HTMLScanner.java:2114)
at net.sourceforge.htmlunit.cyberneko.HTMLScanner.scanDocument(HTMLScanner.java:937)
at net.sourceforge.htmlunit.cyberneko.HTMLConfiguration.parse(HTMLConfiguration.java:443)
at net.sourceforge.htmlunit.cyberneko.HTMLConfiguration.parse(HTMLConfiguration.java:394)
at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
at com.gargoylesoftware.htmlunit.html.parser.neko.HtmlUnitNekoDOMBuilder.parse(HtmlUnitNekoDOMBuilder.java:760)
at com.gargoylesoftware.htmlunit.html.parser.neko.HtmlUnitNekoHtmlParser.parseFragment(HtmlUnitNekoHtmlParser.java:158)
at com.gargoylesoftware.htmlunit.html.parser.neko.HtmlUnitNekoHtmlParser.parseFragment(HtmlUnitNekoHtmlParser.java:112)
at com.gargoylesoftware.htmlunit.javascript.host.Element.parseHtmlSnippet(Element.java:868)
at com.gargoylesoftware.htmlunit.javascript.host.Element.setInnerHTML(Element.java:920)
at com.gargoylesoftware.htmlunit.javascript.host.html.HTMLElement.setInnerHTML(HTMLElement.java:676)
at sun.reflect.GeneratedMethodAccessor17.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at net.sourceforge.htmlunit.corejs.javascript.MemberBox.invoke(MemberBox.java:188)
... 30 more
Enclosed exception:
java.lang.RuntimeException: Exception invoking setInnerHTML
at net.sourceforge.htmlunit.corejs.javascript.MemberBox.invoke(MemberBox.java:214)
at net.sourceforge.htmlunit.corejs.javascript.ScriptableObject$GetterSlot.setValue(ScriptableObject.java:323)
at net.sourceforge.htmlunit.corejs.javascript.ScriptableObject.putImpl(ScriptableObject.java:2868)
at net.sourceforge.htmlunit.corejs.javascript.ScriptableObject.put(ScriptableObject.java:536)
at com.gargoylesoftware.htmlunit.javascript.HtmlUnitScriptable.put(HtmlUnitScriptable.java:151)
at net.sourceforge.htmlunit.corejs.javascript.ScriptableObject.putProperty(ScriptableObject.java:2539)
at net.sourceforge.htmlunit.corejs.javascript.ScriptRuntime.setObjectElem(ScriptRuntime.java:1721)
at net.sourceforge.htmlunit.corejs.javascript.ScriptRuntime.setObjectElem(ScriptRuntime.java:1706)
at net.sourceforge.htmlunit.corejs.javascript.Interpreter.doSetElem(Interpreter.java:2460)
at net.sourceforge.htmlunit.corejs.javascript.Interpreter.interpretLoop(Interpreter.java:1488)
at net.sourceforge.htmlunit.corejs.javascript.Interpreter.interpret(Interpreter.java:1013)
at net.sourceforge.htmlunit.corejs.javascript.InterpretedFunction.call(InterpretedFunction.java:111)
at net.sourceforge.htmlunit.corejs.javascript.ContextFactory.doTopCall(ContextFactory.java:427)
at com.gargoylesoftware.htmlunit.javascript.HtmlUnitContextFactory.doTopCall(HtmlUnitContextFactory.java:340)
at net.sourceforge.htmlunit.corejs.javascript.ScriptRuntime.doTopCall(ScriptRuntime.java:3640)
at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine$3.doRun(JavaScriptEngine.java:851)
at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine$HtmlUnitContextAction.run(JavaScriptEngine.java:914)
at net.sourceforge.htmlunit.corejs.javascript.Context.call(Context.java:619)
at net.sourceforge.htmlunit.corejs.javascript.ContextFactory.call(ContextFactory.java:537)
at com.gargoylesoftware.htmlunit.javascript.HtmlUnitContextFactory.callSecured(HtmlUnitContextFactory.java:354)
at com.gargoylesoftware.htmlunit.javascript.JavaScriptEngine.callFunction(JavaScriptEngine.java:858)
at com.gargoylesoftware.htmlunit.javascript.host.xml.XMLHttpRequest.setState(XMLHttpRequest.java:213)
at com.gargoylesoftware.htmlunit.javascript.host.xml.XMLHttpRequest.doSend(XMLHttpRequest.java:804)
at com.gargoylesoftware.htmlunit.javascript.host.xml.XMLHttpRequest.access$000(XMLHttpRequest.java:105)
at com.gargoylesoftware.htmlunit.javascript.host.xml.XMLHttpRequest$1.run(XMLHttpRequest.java:636)
at net.sourceforge.htmlunit.corejs.javascript.Context.call(Context.java:619)
at net.sourceforge.htmlunit.corejs.javascript.ContextFactory.call(ContextFactory.java:537)
at com.gargoylesoftware.htmlunit.javascript.background.JavascriptXMLHttpRequestJob.run(JavascriptXMLHttpRequestJob.java:36)
at com.gargoylesoftware.htmlunit.javascript.background.JavaScriptJobManagerImpl.runSingleJob(JavaScriptJobManagerImpl.java:429)
at com.gargoylesoftware.htmlunit.javascript.background.DefaultJavaScriptExecutor.run(DefaultJavaScriptExecutor.java:148)
at java.lang.Thread.run(Thread.java:745)
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
======= EXCEPTION END ========
问题是：如何让我的代码始终告诉我代码的哪一行导致了问题。
解决方案
不在堆栈跟踪上的原因page.save(saveFolder) 是它启动了一个新线程并且在新线程中抛出了异常。在新线程中，您的任何代码都不会被执行，因此它不会显示您的哪一行代码出错了。
实际上，在这种情况下，JVM 无法知道您的哪一行代码是原因。您可能认为page.save(saveFolder);是原因，但更可能是因为您忘记在调用之前设置一些参数page.save(saveFolder);。
您唯一能做的就是检查异常以查看发生了什么问题，知道代码的哪一行导致异常对您没有多大帮助。这就是为什么调试多线程程序很困难的原因。
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