Unable to intantiate Action 不能实例化Action的错误

Unable to intantiate Action!
    com.opensymphony.xwork2.DefaultActionInvocation.createAction(DefaultActionInvocation.java:290)
    com.opensymphony.xwork2.DefaultActionInvocation.init(DefaultActionInvocation.java:388)
    com.opensymphony.xwork2.DefaultActionProxy.prepare(DefaultActionProxy.java:187)
    org.apache.struts2.impl.StrutsActionProxy.prepare(StrutsActionProxy.java:61)
    org.apache.struts2.impl.StrutsActionProxyFactory.createActionProxy(StrutsActionProxyFactory.java:39)
    com.opensymphony.xwork2.DefaultActionProxyFactory.createActionProxy(DefaultActionProxyFactory.java:47)
    org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:478)
    org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
    org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)
    org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
    org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:857)
    org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:565)
    org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1509)
    java.lang.Thread.run(Thread.java:619)

java.lang.InstantiationException: *Action

 

错误原因：竟然是我写的action类没有无参构造器，所以无法实例化action。