<p:commandButton value="GO" action="#{indexBB.clickSearchButton}" />

public String clickSearchButton() {
        DateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss");
        FacesContext.getCurrentInstance().getExternalContext().getRequestMap().put("dateini", dateFormat.format(dateIni));
return "B?faces-redirect=true";
}

@PostConstruct
public void init() {
    Map<String,Object> parameterMap = FacesContext.getCurrentInstance().getExternalContext().getRequestMap();
    if(parameterMap.get("dateini") != null ){
        //assign the value
    }
}