Prevent multiple users login with same username and password JSF JEE

Question

I am handling users login in this way :

@ManagedBean
@SessionScoped
public class Logincontroller implements Serializable{
String username;  
String password;

public String getUsername() {
    return username;
}

public void setUsername(String username) {
    this.username = username;
}

public String getPassword() {
    return password;
}

public void setPassword(String password) {
    this.password = password;
}


public void setSessiontimedisplay(boolean sessiontimedisplay) {
    this.sessiontimedisplay = sessiontimedisplay;
}

public Logincontroller() {
}

public String Login() {
    try {

        HttpServletRequest request = (HttpServletRequest) FacesContext.getCurrentInstance().getExternalContext().getRequest();
        request.login(username, password);

         return "/profil/Homepage.xhtml?faces-redirect=true";}   

    } catch(Exception e) {
        this.groupname="";
        this.username="";  
        FacesContext.getCurrentInstance().addMessage(null, new FacesMessage(FacesMessage.SEVERITY_ERROR,"Either Login or Password is wrong", ""));
    }
    return null;
}
public String logout(){   

    FacesContext.getCurrentInstance().getExternalContext().invalidateSession();
    return "/login?faces-redirect=true";

    }

JSF PAGE CODE :

<f:facet name="header"> Users connections</f:facet>  

<h:outputLabel for="username" value="username " /><p:inputText id="username" value="#{logincontroller.username}"  />
<h:outputLabel for="password" value="password" />  <p:inputText id="password" value="#{logincontroller.password}" type="password"/>

<f:facet name="footer">       
    <p:commandButton value="Connexion" icon="ui-icon-check" style="margin:0" action="#{logincontroller.Login()}" update="@form"/> 

</f:facet>  
</p:panelGrid>

The problem that i have is users can be connected with the same username in other browser or in an other machine and i want that username can be opened just in one single window . Why my class isnt handling this and what i need to add to Prevent multiple users login with same username and password ?