struts2.0 datatimepicker 标签问题

我的源代码如下：
<%@ page language="java"  pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <s:head/>
    <title>My</title>
  </head>
 
  <body>
    <s:datetimepicker name="date" 
                      label="显示时间" 
                      value="2006-01-12"
                      displayFormat="yyyy年MM月dd日" 
                      language="zh_CN"
                      theme="ajax"/> 
    <br>
  </body>
</html>
页面可以显示正常，但是后台出现异常：
2009-3-27 10:22:55 org.apache.struts2.components.DateTimePicker format
严重: Could not parse date
java.text.ParseException: Unparseable date: "2006-01-12"
at java.text.DateFormat.parse(Unknown Source)
at org.apache.struts2.components.DateTimePicker.format(DateTimePicker.java:315)
at org.apache.struts2.components.DateTimePicker.evaluateParams(DateTimePicker.java:206)
at org.apache.struts2.components.UIBean.end(UIBean.java:481)
at org.apache.struts2.views.jsp.ComponentTagSupport.doEndTag(ComponentTagSupport.java:43)
at org.apache.jsp.datatimepicker_jsp._jspx_meth_s_005fdatetimepicker_005f0(datatimepicker_jsp.java:150)
at org.apache.jsp.datatimepicker_jsp._jspService(datatimepicker_jsp.java:94)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:384)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:416)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:228)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:216)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
at java.lang.Thread.run(Unknown Source)
我想问一下：value属性中的日期格式到底怎么样写才不会出现异常！还有就是s:action怎么样使用？