Spring Webflow IllegalStateException：BeanResult的BindingResult和普通目标对象都不能用作请求属性

我的最终目标是建立一个带有注释的模型，并对表单输入进行验证。我已经尝试过通过编写一些验证器来进行此操作，但是它没有用（该表单甚至不会显示我可以输入sp的字段，因此没有任何可以测试验证的字段），所以我从头开始尝试了一下。第一步，我只想在开始任何形式的验证之前使模型绑定生效。

作为一个简单的尝试，我使用了mailItemModel形式http://www.javabeat.net/introduction-to-spring-web-flow-swf/

我在servlet-config.xml中添加了以下行，该行链接在web.xml中：

<mvc:annotation-driven />   
<context:annotation-config />
<context:component-scan base-package="com.mypackage.kumo.**" /> 

我从另一本教程中学到了这一点，我有点想这将是扫描整个程序包，而我不需要显式地指定变量中的所有模型。我得到了名义上的错误。我也尝试将“ @Component”添加到模型类。但这并没有改变任何东西。

然后我尝试将其添加到流XML中

<var name="MailItemModel" />

从上面的链接教程开始。我收到了错误消息，该元素var“需要一个” class“属性。因此我将其改为：

<var name="MailItemModel" class="com.mypackage.kumo.model.MailItemModel" />

但这只会引发与以前非常相同的错误。

我的流程现在看起来像这样：

<?xml version="1.0" encoding="UTF-8"?>
<flow xmlns="http://www.springframework.org/schema/webflow"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:ns0="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation=" 
        http://www.springframework.org/schema/webflow 
        http://www.springframework.org/schema/webflow/spring-webflow-2.0.xsd"
    start-state="Start">

    <var name="MailItemModel" class="com.mypackage.kumo.model.MailItemModel" />

    <view-state id="Start" view="/Search" model="MailItemModel">
        <transition on="entered" to="temp" />
        <transition on="cancel" to="SubEnde" />
    </view-state>

    <view-state id="temp" view="/End" />

    <view-state id="SubEnde" view="/Start" />    
</flow>

Search.jsp（表格摘录）

<form:form method = "post" modelAttribute = "mailItemModel">
      Mail Username: <form:input path="username" />
         <br />
       <input type="submit" name="_eventId_entered" value="Entered" />
       <input type="submit" name="_eventId_cancel" value="Cancel" />
</form:form>

Start.jsp和End.jsp只是具有某些lorem ipsum内容的静态jsps。

Stacktrace：

root cause

java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'mailItemModel' available as request attribute
    org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:144)
    org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getBindStatus(AbstractDataBoundFormElementTag.java:168)
    org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getPropertyPath(AbstractDataBoundFormElementTag.java:188)
    org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getName(AbstractDataBoundFormElementTag.java:154)
    org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.autogenerateId(AbstractDataBoundFormElementTag.java:141)
    org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.resolveId(AbstractDataBoundFormElementTag.java:132)
    org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.writeDefaultAttributes(AbstractDataBoundFormElementTag.java:116)
    org.springframework.web.servlet.tags.form.AbstractHtmlElementTag.writeDefaultAttributes(AbstractHtmlElementTag.java:422)
    org.springframework.web.servlet.tags.form.InputTag.writeTagContent(InputTag.java:142)
    org.springframework.web.servlet.tags.form.AbstractFormTag.doStartTagInternal(AbstractFormTag.java:84)
    org.springframework.web.servlet.tags.RequestContextAwareTag.doStartTag(RequestContextAwareTag.java:80)
    org.apache.jsp.WEB_002dINF.jsp.Search_jsp._jspx_meth_form_005finput_005f0(Search_jsp.java:559)
    org.apache.jsp.WEB_002dINF.jsp.Search_jsp._jspx_meth_form_005fform_005f0(Search_jsp.java:522)
    org.apache.jsp.WEB_002dINF.jsp.Search_jsp._jspx_meth_dsx_005fcontent_002dbox_005f0(Search_jsp.java:478)
    org.apache.jsp.WEB_002dINF.jsp.Search_jsp._jspx_meth_dsx_005fcontent_005f0(Search_jsp.java:439)
    org.apache.jsp.WEB_002dINF.jsp.Search_jsp._jspx_meth_dsx_005fhtml_002dbody_005f0(Search_jsp.java:375)
    org.apache.jsp.WEB_002dINF.jsp.Search_jsp._jspx_meth_dsx_005fhtml_005f0(Search_jsp.java:293)
    org.apache.jsp.WEB_002dINF.jsp.Search_jsp._jspService(Search_jsp.java:126)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:209)
    org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:267)
    org.springframework.webflow.mvc.servlet.ServletMvcView.doRender(ServletMvcView.java:55)
    org.springframework.webflow.mvc.view.AbstractMvcView.render(AbstractMvcView.java:187)
    org.springframework.webflow.engine.ViewState.render(ViewState.java:296)
    org.springframework.webflow.engine.ViewState.refresh(ViewState.java:243)
    org.springframework.webflow.engine.ViewState.resume(ViewState.java:221)
    org.springframework.webflow.engine.Flow.resume(Flow.java:545)
    org.springframework.webflow.engine.impl.FlowExecutionImpl.resume(FlowExecutionImpl.java:258)
    org.springframework.webflow.executor.FlowExecutorImpl.resumeExecution(FlowExecutorImpl.java:169)
    org.springframework.webflow.mvc.servlet.FlowHandlerAdapter.handle(FlowHandlerAdapter.java:183)
    org.springframework.webflow.mvc.servlet.FlowController.handleRequest(FlowController.java:174)
    org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:50)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

我究竟做错了什么？我已经研究了其他相同错误的帖子，但是它们都使用@requestmapping到控制器中的URL，但是由于我使用的是Webflow，所以我不（而且似乎不能）使用控制器，所以它没有真的没有帮助。