struts2出现Could not find action or result的错误原因

今天在学习struts2时，在尝试struts2动态方法调用时出现这个问题。

PS：struts2动态方法调用有3种方式：1.指定method属性、2.感叹号方式、3.通配符方式

而比较奇怪的是使用第一种方式无错误，而使用后两种方式时出现这个错误。

下面是控制台输出的异常信息

</pre><pre>

警告: Could not find action or result: /Struts2-study_2/helloworld.action
There is no Action mapped for namespace [/] and action name [helloworld] associated with context path [/Struts2-study_2]. - [unknown location]
at com.opensymphony.xwork2.DefaultActionProxy.prepare(DefaultActionProxy.java:185)
at org.apache.struts2.impl.StrutsActionProxy.prepare(StrutsActionProxy.java:63)
at org.apache.struts2.impl.StrutsActionProxyFactory.createActionProxy(StrutsActionProxyFactory.java:37)
at com.opensymphony.xwork2.DefaultActionProxyFactory.createActionProxy(DefaultActionProxyFactory.java:58)
at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:554)
at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:81)
at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)
at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2503)
at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2492)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)

出现问题之后再三检查代码，觉得代码无误，于是再重新看控制台输出的信息，发现其中一条警告信息

警告: Local DTD is missing for publicID: -//Apache Software Foundation//DTD Struts Configuration 2.5//EN - defined mappings: {-//Apache Struts//XWork 1.1.1//EN=xwork-1.1.1.dtd, -//Apache Software Foundation//DTD Struts Configuration 2.0//EN=struts-2.0.dtd, -//Apache Struts//XWork 1.0//EN=xwork-1.0.dtd, -//Apache Software Foundation//DTD Struts Configuration 2.1//EN=struts-2.1.dtd, -//Apache Struts//XWork 1.1//EN=xwork-1.1.dtd, -//Apache Struts//XWork 2.1.3//EN=xwork-2.1.3.dtd, -//Apache Software Foundation//DTD Struts Configuration 2.3//EN=struts-2.3.dtd, -//Apache Struts//XWork 2.0//EN=xwork-2.0.dtd, -//Apache Software Foundation//DTD Struts Configuration 2.1.7//EN=struts-2.1.7.dtd, -//Apache Struts//XWork 2.1//EN=xwork-2.1.dtd, -//Apache Struts//XWork 2.3//EN=xwork-2.3.dtd}

发现文档类型声明时声明错了struts2的版本（使用的是2.3版本，声明成了2.5版本），改正后重启tomcat，程序运行正常。