javax.servlet.ServletException: Filter execution threw an exception

HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception javax.servlet.ServletException: Filter execution threw an exception
root cause java.lang.NoClassDefFoundError: Could not initialize class com.yxq.action.IndexAction
sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
java.lang.reflect.Constructor.newInstance(Constructor.java:513)
java.lang.Class.newInstance0(Class.java:355)
java.lang.Class.newInstance(Class.java:308)
com.opensymphony.xwork2.ObjectFactory.buildBean(ObjectFactory.java:123)
com.opensymphony.xwork2.ObjectFactory.buildBean(ObjectFactory.java:154)
com.opensymphony.xwork2.ObjectFactory.buildBean(ObjectFactory.java:143)
com.opensymphony.xwork2.ObjectFactory.buildAction(ObjectFactory.java:113)
com.opensymphony.xwork2.DefaultActionInvocation.createAction(DefaultActionInvocation.java:275)
com.opensymphony.xwork2.DefaultActionInvocation.init(DefaultActionInvocation.java:365)
com.opensymphony.xwork2.DefaultActionInvocation.access$000(DefaultActionInvocation.java:38)
com.opensymphony.xwork2.DefaultActionInvocation$1.doProfiling(DefaultActionInvocation.java:83)
com.opensymphony.xwork2.util.profiling.UtilTimerStack.profile(UtilTimerStack.java:455)
com.opensymphony.xwork2.DefaultActionInvocation.<init>(DefaultActionInvocation.java:74)
com.opensymphony.xwork2.DefaultActionProxy.prepare(DefaultActionProxy.java:189)
org.apache.struts2.impl.StrutsActionProxyFactory.createActionProxy(StrutsActionProxyFactory.java:41)
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:494)
org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:419)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.33 logs.
--------------------------------------------------------------------------------Apache Tomcat/6.0.33