Java 无法获取导致错误的代码中的实际行

在下面的示例代码中，我得到了大量的stacktrace错误，我知道这些错误来自

page.save（saveFolder）

line，但在错误中没有一行给出这一行作为错误。因此，当你有10倍长的代码时，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 ) {

        }
    }
}

错误行如下所示：-

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是哪一行代码导致了问题。

原因是

页面。save（saveFolder）

不在堆栈跟踪上，因为它启动了一个新线程，并且在新线程中引发了异常。在新线程中，没有执行任何代码，因此不会显示哪行代码出错

事实上，在这种情况下，JVM无法知道哪行代码是原因。您可能认为

page.save（保存文件夹）是原因，但更可能是因为在调用
page.save（saveFolder）之前忘记设置一些参数

你唯一能做的就是检查异常，看看哪里出了问题，知道是哪行代码导致了异常对你没有多大帮助。这就是调试多线程程序很困难的原因。
您需要有一个有意义的
try catch
块作为开始。这是否回答了您的问题？查看方法：HtmlScript.onAllChildrenAddedToPage（），不幸的是，您没有将其包含在共享的代码中。原因：java.lang.NullPointerException是否在我的catch中放入printstacktrace（）并不重要-stacktrace来自page.save（文件夹）命令，即使我把命令放在捕获中，它们也永远不会被执行。stacktrace来自page.save命令。以我的知识水平，我无法理解。是否有可能为了调试代码而将应用程序强制为单线程？我认为这是不可能的。如果库使用多线程，如何使其成为单线程。