Java，java.lang.reflect.InitationTargetException 与 Digester 解析器
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
I've a Java app, working with Lucene and Apache commons Digester to parse a xml collection. After the first item is parsed, I get this error... What does it mean ?
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
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评论（2）
我看起来很清楚：
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。
Looks pretty clear to me:
Your problem is right there. You need to more defensive in your code to protect against null references.
P.S. It's very bad practice to put your code into the default package. You should always put classes into an explicit package.
CollectionIndexer是您自己的类吗？它似乎在第 41 行抛出NullPointerException。它由 SAX 事件解析器调用，因此被InitationTargetException包装。顺便说一句：JVM 从最外层开始打印堆栈跟踪，最后显示最内层的异常。但由于最里面的异常是在开始时抛出的，因此它几乎总是最有趣的异常。因此，根据经验：始终查看异常堆栈跟踪中的最后一个
caused by子句，因为它通常是最有趣的。Is
CollectionIndexeryour own class? It seems like it throwsNullPointerExceptionon line 41. It is invoked by SAX event parser, hence being wrapped byInvocationTargetException.BTW: JVM prints stack traces starting from the outermost one, displaying the innermost exception at the end. But since the innermost exception is thrown at the beginning, it is almost always the most interesting one. So as a rule of thumb: always look at the last
caused byclause in exception stack trace, as it is typically the most interesting.