primefaces单选按钮不工作（单选按钮值未解析为bean类）？

Question

Xhtml页面：

<p:outputPanel id="customPanel" style="margin-bottom:10px;">
     <p:selectOneRadio id="radiobutton" value="#{a.date}" layout="custom">
     <f:selectItem itemLabel="Select Month:" itemValue="date" />
     <f:selectItem itemLabel="Select Date :" itemValue="date1" />
     <f:convertDateTime pattern="dd/MM/yyyy"/>
      </p:selectOneRadio>
       <p:panelGrid columns="3" cellpadding="0"
                                        style="border:hidden; padding:1px;">
                                        <p:radioButton id="opt1" for="radiobutton" itemIndex="0" />
                                        <h:outputLabel for="opt1" value="Select Month:" />
                                        <p:calendar pattern="MMM-yyyy" navigator="true" />

                                        <p:radioButton id="opt2" for="radiobutton" itemIndex="1" />
                                        <h:outputLabel for="opt2" value="Select Date :" />
                                        <p:calendar  navigator="true"/>
                                    </p:panelGrid>
           </p:outputPanel>

Bean类：

@ManagedBean(name="a")
            public class A
    {
            private String date ;


            public String getDate() {
                    return date;
                }

                public void setDate(String date) {
                    this.date = date;
                }
            System.out.println(" Date : " + date);
    }

选择的日期值没有得到xhtml页面到bean类。当我选择任何单选按钮后单击提交按钮时显示错误.. form：radiobutton：＆＃39; date＆＃39;不能被理解为date.please建议解析将单选按钮值xhtml页面解析为bean类。