public String execute()  
  {
        ActionContext  ctx = ActionContext.getContext();
    Map session = ctx.getSession();
    String id = (String)session.get("user_id");
    OvrTimeModel ovrt = new OvrTimeModel();
        years = ovrt.getYear();
        months = ovrt.getMonthList();
        Map params = ctx.getParameters();
        if(params.get("year")==null)
        {  
          thisYear = ovrt.getYYY();
          thisMonth =  ovrt.getMM();
        }
        else
        {
        thisYear = (String)params.get("year");//<---會丟出ClassCastException
        thisMonth = (String)params.get("month");
        }
    return SUCCESS;
  }

exception 

java.lang.ClassCastException
  at com.webwork.apps.fees.OverTimeFees58.execute(OverTimeFees58.java:38)
  at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:168)
  at com.opensymphony.xwork.DefaultActionProxy.execute(DefaultActionProxy.java:115)
  at com.opensymphony.webwork.dispatcher.ServletDispatcher.serviceAction(ServletDispatcher.java:229)
  at com.opensymphony.webwork.dispatcher.ServletDispatcher.service(ServletDispatcher.java:199)
  at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)

<xwork>

    <include file="webwork-default.xml"/>
  
    <package name="feesWork" extends="webwork-default" namespace="/fees" >
    <action name="initOvrTimeFees58" class="com.webwork.apps.fees.OverTimeFees58" >
      <interceptor-ref name="defaultStack" /> 
      <result name="success" type="dispatcher">
        <param name="location">/xwork/fees/OverTimeFees58.jsp</param>
      </result>
    </action>>
  </package>

</xwork>

<form name="form1" method="post" action="initOvrTimeFees58.action">
  <div align="center">
  <table border="0" cellpadding="0" cellspacing="0" width="250" bgcolor="#FFFFFF">
      <ww:select label="'年'" name="'year'" list="years" value="thisYear" />
      <ww:select label="'月份'" name="'month'" list="months" value="thisMonth" />
      <ww:submit value="'送出'"/>
  </table>      
  </div>
<br>
</form>