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我有一个 Java 应用程序，使用 Lucene 和 Apache commons Digester 来解析 xml 集合。解析第一项后，我收到此错误...这是什么意思？

Feb 24, 2011 5:53:16 PM org.apache.commons.digester.Digester endElement
SEVERE: End event threw exception
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.commons.beanutils.MethodUtils.invokeMethod(MethodUtils.java:216)
    at org.apache.commons.digester.SetNextRule.end(SetNextRule.java:220)
    at org.apache.commons.digester.Rule.end(Rule.java:257)
    at org.apache.commons.digester.Digester.endElement(Digester.java:1345)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endElement(AbstractSAXParser.java:601)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDocumentFragmentScannerImpl.java:1782)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2938)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:648)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:511)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:808)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:737)
    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:119)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1205)
    at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:522)
    at org.apache.commons.digester.Digester.parse(Digester.java:1871)
    at CollectionIndexer.main(CollectionIndexer.java:103)
Caused by: java.lang.NullPointerException
    at CollectionIndexer.addDocument(CollectionIndexer.java:41)
    ... 20 more
Exception in thread "main" java.lang.NullPointerException
    at org.apache.commons.digester.Digester.createSAXException(Digester.java:3363)
    at org.apache.commons.digester.Digester.createSAXException(Digester.java:3389)
    at org.apache.commons.digester.Digester.endElement(Digester.java:1348)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endElement(AbstractSAXParser.java:601)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDocumentFragmentScannerImpl.java:1782)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2938)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:648)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:511)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:808)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:737)
    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:119)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1205)
    at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:522)
    at org.apache.commons.digester.Digester.parse(Digester.java:1871)
    at CollectionIndexer.main(CollectionIndexer.java:103)
Caused by: java.lang.NullPointerException
    at CollectionIndexer.addDocument(CollectionIndexer.java:41)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.commons.beanutils.MethodUtils.invokeMethod(MethodUtils.java:216)
    at org.apache.commons.digester.SetNextRule.end(SetNextRule.java:220)
    at org.apache.commons.digester.Rule.end(Rule.java:257)
    at org.apache.commons.digester.Digester.endElement(Digester.java:1345)
    ... 12 more
4

2 回答 2

4

对我来说看起来很清楚：

Caused by: java.lang.NullPointerException
    at CollectionIndexer.addDocument(CollectionIndexer.java:41)

你的问题就在那里。您需要在代码中采取更多防御措施来防止空引用。

PS 将代码放入默认包中是非常糟糕的做法。您应该始终将类放入显式包中。

于 2011-02-24T22:05:07.273 回答
2

是CollectionIndexer你自己的课吗？它似乎NullPointerException在第 41 行抛出。它由 SAX 事件解析器调用，因此被InvocationTargetException.

顺便说一句：JVM 从最外面的一个开始打印堆栈跟踪，最后显示最里面的异常。但是由于最里面的异常是一开始就抛出的，所以它几乎总是最有趣的。所以作为一个经验法则：总是查看caused by异常堆栈跟踪中的最后一个子句，因为它通常是最有趣的。

于 2011-02-24T22:06:38.533 回答