JAVA

Execute method on load

<f:metadata>
    <f:viewParam name="token" value="#{authenticator.token}" />
    <f:viewAction action="#{authenticator.check}" />
</f:metadata>

Execute method on load

@ManagedBean
@RequestScoped
public class Authenticator {

    private String token;

    public String check() {
        return isValid(token) ? null : "main.jsf";
    }

    // Getter/setter.
}