使用poi读取Excel时报错java.lang.NoClassDefFoundError: org/w3c/dom/ElementTraversal

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报错日志：
java.lang.NoClassDefFoundError: org/w3c/dom/ElementTraversal
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
at java.net.URLClassLoader.access$100(URLClassLoader.java:71) at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:425) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
at org.apache.xerces.parsers.AbstractDOMParser.startDocument(Unknown Source)
at org.apache.xerces.impl.dtd.XMLDTDValidator.startDocument(Unknown Source)
at org.apache.xerces.impl.XMLDocumentScannerImpl.startEntity(Unknown Source)
at org.apache.xerces.impl.XMLVersionDetector.startDocumentParsing(Unknown Source)
at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
at org.apache.xerces.parsers.DOMParser.parse(Unknown Source)
at org.apache.xerces.jaxp.DocumentBuilderImpl.parse(Unknown Source)
at javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:121)
Caused by: java.lang.ClassNotFoundException: org.w3c.dom.ElementTraversal
at java.net.URLClassLoader$1.run(URLClassLoader.java:366) at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
… 26 more

maven导入poi包：

<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi-ooxml</artifactId>
    <version>3.9</version>
</dependency>

一开始以为是不是缺少了什么类？项目重新编译运行还是报错
百度一下poi用法，也是说这样导入maven的
额？怪了，难道人品问题？不不不。。。再搜搜
还是没办法，最后在其他项目pom.xml里看到了这句

<dependency>  
    <groupId>xml-apis</groupId>  
    <artifactId>xml-apis</artifactId>  
    <version>1.4.01</version>  
</dependency>  

难道是这个包的问题？加入马上就可以了
我也是醉了。难道是poi的问题？
不不不，最后发现了我是有加载了一个数据库配置文件config.xml。应该就是没加载成功
需要xml-apis来解析xml

思考：出bug要先去看懂报错日志，而且报错日志也写得很清楚是xml解析的问题了，自己粗心大意了