Struts2 jQuery struts-plugin.xml invalid

I have setup a project which is a combo of Struts2 + Springs + JPA.

I recently came across the Struts2-Jquery Plugin

Using this plugin (struts2-jquery-plugin-3.5.1.jar) in my project I got an error

Unable to load jar:file:/H:/My%20Project/phase1/build/web/WEB-INF/lib/struts2-jquery-plugin-3.5.1.jar!/struts-plugin.xml - Class: java.net.PlainSocketImpl
File: PlainSocketImpl.java
Method: connect
Line: 195 - java/net/PlainSocketImpl.java:195:-1
    at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.loadConfigurationFiles(XmlConfigurationProvider.java:909)
    at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.loadDocuments(XmlConfigurationProvider.java:154)
    at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.init(XmlConfigurationProvider.java:121)
    at com.opensymphony.xwork2.config.impl.DefaultConfiguration.reloadContainer(DefaultConfiguration.java:179)
    at com.opensymphony.xwork2.config.ConfigurationManager.getConfiguration(ConfigurationManager.java:66)
    ... 48 more


 Caused by: java.net.UnknownHostException: struts.apache.org
        at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:195)
        at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
        at java.net.Socket.connect(Socket.java:529)
        at java.net.Socket.connect(Socket.java:478)
        at sun.net.NetworkClient.doConnect(NetworkClient.java:163)
        at sun.net.www.http.HttpClient.openServer(HttpClient.java:394)
        at sun.net.www.http.HttpClient.openServer(HttpClient.java:529)
        at sun.net.www.http.HttpClient.<init>(HttpClient.java:233)
        at sun.net.www.http.HttpClient.New(HttpClient.java:306)
        at sun.net.www.http.HttpClient.New(HttpClient.java:323)
        at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:970)
        at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:911)
        at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:836)
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1172)
        at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.setupCurrentEntity(XMLEntityManager.java:677)
        at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.startEntity(XMLEntityManager.java:1315)
        at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.startDTDEntity(XMLEntityManager.java:1282)
        at com.sun.org.apache.xerces.internal.impl.XMLDTDScannerImpl.setInputSource(XMLDTDScannerImpl.java:283)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.dispatch(XMLDocumentScannerImpl.java:1194)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.next(XMLDocumentScannerImpl.java:1090)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:1003)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:648)
        at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:140)
        at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:511)
        at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:808)
        at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:737)
        at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:119)
        at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1205)
        at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:522)
        at javax.xml.parsers.SAXParser.parse(SAXParser.java:395)
        at com.opensymphony.xwork2.util.DomHelper.parse(DomHelper.java:113)
        ... 53 more

The solution to this particular error was given here as Struts2 DTD problem.

Acting in the solution given in the above link.. updated three libraries in my webapp lib folder:

Struts2-core-2.3.4.1
struts2-spring-plugin-2.3.4.1
xwork-core-2.3.4.1

When trying to deploy after this update I got this stacktrace

SEVERE: Exception starting filter struts2
java.lang.NoClassDefFoundError: org/apache/commons/lang3/StringUtils
    at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.register(XmlConfigurationProvider.java:209)
    at org.apache.struts2.config.StrutsXmlConfigurationProvider.register(StrutsXmlConfigurationProvider.java:102)
    at com.opensymphony.xwork2.config.impl.DefaultConfiguration.reloadContainer(DefaultConfiguration.java:210)
    at com.opensymphony.xwork2.config.ConfigurationManager.getConfiguration(ConfigurationManager.java:66)
    at org.apache.struts2.dispatcher.Dispatcher.init_PreloadConfiguration(Dispatcher.java:390)
    at org.apache.struts2.dispatcher.Dispatcher.init(Dispatcher.java:437)
    at org.apache.struts2.dispatcher.ng.InitOperations.initDispatcher(InitOperations.java:74)
    at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.init(StrutsPrepareAndExecuteFilter.java:51)
    at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:277)
    at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:258)
    at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:382)
    at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:103)
    at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4649)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5305)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:899)
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:875)
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:618)
    at org.apache.catalina.startup.HostConfig.deployDescriptor(HostConfig.java:650)
    at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:531)
    at org.apache.catalina.startup.HostConfig.check(HostConfig.java:1468)
    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.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:301)
    at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:836)
    at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:761)
    at org.apache.catalina.manager.ManagerServlet.check(ManagerServlet.java:1436)
    at org.apache.catalina.manager.ManagerServlet.deploy(ManagerServlet.java:856)
    at org.apache.catalina.manager.ManagerServlet.doGet(ManagerServlet.java:353)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:108)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:581)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1001)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:579)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.ClassNotFoundException: org.apache.commons.lang3.StringUtils
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1711)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1556)
    ... 52 more

Can anyone give me a pointer where I am going wrong ?

You need to add the commons-lang3-3.x.jar to your classpath for the filter to run.

You must ensure you don't have multiple versions of commons-lang3-x.x.jar too.

commons-lang3-x.x.jar and commons-lang-x.x.jar instead can coexist in the same classpath, because the package is different (they did it on purpose ;)

This can be known, because of NoClassDefFoundError:

java.lang.NoClassDefFoundError: org/apache/commons/lang3/StringUtils.

which occurs mostly in two cases:

at runtime, you doesn't have the library,
or you have two versions of the library, hence the classloader doesn't know which to pick, and raises the exception.

The lang3 in the package means that the StringUtils class missing is from common-lang3-*.jar, not from common-lang-*.jar.