<p:dataTable id="tabJob" var="contenuJob" value="#{templateBean.contenuJob}" selection="#{templateBean.selectedRows}"
rowKey="#{templateBean.idJob}" style="margin-bottom:0"
scrollable="true" scrollHeight="250" rowIndexVar="rowIndex" >

                        <p:column selectionMode="multiple" style="width:16px;text-align:center" />
                 <f:facet name="header">
                    selectionner les colonnes
                  </f:facet>

                <p:column headerText="#" style="width:3%"> #{rowIndex+1}</p:column>
                <p:columns value="#{templateBean.colonnes}" var="colonnes" columnIndexVar="ind" id="col#{ind}">
                        <f:facet name="header">
                              <h:outputText value="#{colonnes}"/>
                        </f:facet>#{contenuJob[ind]}
                </p:columns>

                <f:facet name="footer">
                    <p:commandButton process="tabJob" value="valider"    action="#{templateBean.validerSelection()}"/>
                </f:facet>

        </p:dataTable>

private ArrayList<String> contenuJob,selectedRows;
.................
public String validerSelection(){


        System.out.println("size de selectedRows ::"+selectedRows.size());

        return null;
    }