引言： DOM4j是java中最为流行的xml解析类库，在使用过程中，碰到了若干问题，这里记录一下，方便后续查询。
1. DOM的版本以及maven引用
<dependency> <groupId>dom4j</groupId> <artifactId>dom4j</artifactId> <version>1.6.1</version> </dependency>2. 使用的代码示例 String msg = msg = "<xml><ToUserName>t6504091</ToUserName><FromUserName>dance-note</FromUserName><CreateTime>111</CreateTime><MsgType>text</MsgType><Content>111</Content></xml>"; SAXReader reader = new SAXReader(); long startTime = System.currentTimeMillis(); Document doc = reader.read(msg); String xpath = "//*[local-name()='xml']/*[local-name()='MsgType']"; @SuppressWarnings("unchecked") List<Element> msgList = doc.selectNodes(xpath); //System.out.println("startTime:" + startTime); String msgType = msgList.get(0).getStringValue(); long endTime = System.currentTimeMillis(); long lastTime = endTime - startTime; System.out.println("MsgType:" + msgType + " takes " + lastTime + " milseconds");3. 其中碰到错误以及解决方法错误信息1：
org.dom4j.DocumentException: no protocol: <xml><ToUserName>t6504091</ToUserName><FromUserName>dance-note</FromUserName><CreateTime>111</CreateTime><MsgType>text</MsgType><Content>111</Content></xml> Nested exception: no protocol: <xml><ToUserName>t6504091</ToUserName><FromUserName>dance-note</FromUserName><CreateTime>111</CreateTime><MsgType>text</MsgType><Content>111</Content></xml> at org.dom4j.io.SAXReader.read(SAXReader.java:484) at org.dom4j.io.SAXReader.read(SAXReader.java:321) at com.rain.wx.skill.UserMessageTest.testMessage(UserMessageTest.java:38) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192) Nested exception: java.net.MalformedURLException: no protocol: <xml><ToUserName>t6504091</ToUserName><FromUserName>dance-note</FromUserName><CreateTime>111</CreateTime><MsgType>text</MsgType><Content>111</Content></xml> at java.net.URL.<init>(URL.java:586) at java.net.URL.<init>(URL.java:483) at java.net.URL.<init>(URL.java:432) at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.setupCurrentEntity(XMLEntityManager.java:619) at com.sun.org.apache.xerces.internal.impl.XMLVersionDetector.determineDocVersion(XMLVersionDetector.java:189) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:812) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:777) at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:141) at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1213) at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:649) at org.dom4j.io.SAXReader.read(SAXReader.java:465) at org.dom4j.io.SAXReader.read(SAXReader.java:321) at com.rain.wx.skill.UserMessageTest.testMessage(UserMessageTest.java:38) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192) 解决办法：将reader中读入的msg进行一下转换：
原来的Java语句：Document doc = reader.read(msg);
更新之后的Java语句： Document doc = reader.read(new ByteArrayInputStream(msg.getBytes("UTF-8")));
错误信息2：
java.lang.NoClassDefFoundError: org/jaxen/NamespaceContext at org.dom4j.DocumentFactory.createXPath(DocumentFactory.java:230) at org.dom4j.tree.AbstractNode.createXPath(AbstractNode.java:207) at org.dom4j.tree.AbstractNode.selectNodes(AbstractNode.java:164) at com.rain.wx.skill.UserMessageTest.testMessage(UserMessageTest.java:44) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192) Caused by: java.lang.ClassNotFoundException: org.jaxen.NamespaceContext at java.net.URLClassLoader.findClass(URLClassLoader.java:381) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331) at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ... 27 more 解决办法：jaxen是xpath的实现类库，这里只需要新增依赖包即可。
<dependency> <groupId>jaxen</groupId> <artifactId>jaxen</artifactId> <version>1.1.6</version> </dependency>4. Jackson XML Mapping和Dom4j的解析性能对比jackson xml的代码：
String msg = "<xml><ToUserName>t6504091</ToUserName><FromUserName>dance-note</FromUserName><CreateTime>111</CreateTime><MsgType>text</MsgType><Content>111</Content></xml>"; ObjectMapper mapper1 = new XmlMapper(); mapper1.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES); BaseIncomingMessage message = mapper1.readValue(msg, BaseIncomingMessage.class); long endTime1 = System.currentTimeMillis(); 解析同样的文件：Jackson一般用时70~80 ms。 而Dom4j基于xpath则需要133ms。综合而言：jackson相比dom4j而言，还是略胜一筹。
5. 参考资料
http://www.cnblogs.com/mouse-coder/p/3451243.html