Sorting is not working in datatable in PrimeFaces?

Sorting is not working in datatable in PrimeFaces. Please suggest.

See below my .xhtml file

<h:form>

  <p:dataTable style="width: 60%" id="dt1" value="#{bean.list}" var="entry" first="0" paginator="true" rows="10" paginatorTemplate="{CurrentPageReport}  {FirstPageLink} {PreviousPageLink} {PageLinks} {NextPageLink} {LastPageLink} {RowsPerPageDropdown}" rowsPerPageTemplate="5,10,15" emptyMessage="No cars found with given criteria" >

    <f:facet name="header">
      <h2>Cars View</h2>
    </f:facet>

    <p:column sortBy="#{entry.carno}" filterBy="#{entry.carno}">
      <f:facet name="header">
        <h:outputText value="Car Number" />
      </f:facet>
      <h:outputText value="#{entry.carno}"></h:outputText>
    </p:column>

    <p:column sortBy="#{entry.carsettings['car-model']}" filterBy="#{entry.carsettings['car-model']}">
      <f:facet name="header">
        <h:outputText value="Car Model"/>
      </f:facet>
      <h:outputText value="#{entry.carsettings['car-model']}"></h:outputText>
    </p:column>

    <p:column sortBy="#{entry.carsettings.year}" filterBy="#{entry.carsettings.year}">
      <f:facet name="header">
        <h:outputText value="Car Year"/>
      </f:facet>
      <h:outputText value="#{entry.carsettings.year}"></h:outputText>
    </p:column>

    <p:column sortBy="#{entry.carsettings.color}" filterBy="#{entry.carsettings.color}">
      <f:facet name="header">
        <h:outputText value="Car Color"/>
      </f:facet>
      <h:outputText value="#{entry.carsettings.color}"></h:outputText>
    </p:column>
  </p:dataTable>
</h:form>

@Sean

Look below code

List of Cars

    <ui:composition template="/template.xhtml">