Desde un <p:commandLink>

//JSF
<h:commandLink action="#{user.goLoginPage}" value="Login page + Param ">
    <f:param name="username" value="mkyong" />
</h:commandLink>

<p:commandLink action="#{controlador.editar(registro)}"
                                       oncomplete="wdlgDetalhe.show()"
                                       update=":frmPrincipal:pnlDetalhe">
                            <p:graphicImage url="./resources/imagens/editar.png"
            style="background-color: transparent; vertical-align: middle; border: none"
                                           width="20" height="20"/>
                       </p:commandLink>