Check if session exists JSF

If someone writes a URL and tries to jump the login page, how can I check that and redirect him to the login page?

You seem to using homegrown authentication. In that case, you need to implement a servlet filter. JSF stores session scoped managed beans as attributes of HttpSession, so you could just check on that in doFilter() method:

HttpServletRequest req = (HttpServletRequest) request;
UserManager userManager = (UserManager) req.getSession().getAttribute("userManager");

if (userManager != null && userManager.isLoggedIn()) {
    chain.doFilter(request, response);
} else {
    HttpServletResponse res = (HttpServletResponse) response;
    res.sendRedirect(req.getContextPath() + "/login.xhtml");
}

Map this filter on an URL pattern covering the secured pages, e.g. /app/*.

---

When I return and try to interact with the form it sends a message alerting me the session expiration. How can I redirect again to the login form when this occurs?

I understand that this concerns Ajax requests? For normal requests you could have used an <error-page> in web.xml. If setting the state saving method to client in web.xml as follows

<context-param>
    <param-name>javax.faces.STATE_SAVING_METHOD</param-name>
    <param-value>client</param-value>
</context-param>

is not an option, then you need to implement a custom ExceptionHandler:

public class ViewExpiredExceptionHandler extends ExceptionHandlerWrapper {

    private ExceptionHandler wrapped;

    public ViewExpiredExceptionHandler(ExceptionHandler wrapped) {
        this.wrapped = wrapped;
    }

    @Override
    public void handle() throws FacesException {
        FacesContext facesContext = FacesContext.getCurrentInstance();

        for (Iterator<ExceptionQueuedEvent> iter = getUnhandledExceptionQueuedEvents().iterator(); iter.hasNext();) {
            Throwable exception = iter.next().getContext().getException();

            if (exception instanceof ViewExpiredException) {
                facesContext.getApplication().getNavigationHandler().handleNavigation(facesContext, null, "viewexpired");
                facesContext.renderResponse();
                iter.remove();
            }
        }

        getWrapped().handle();
    }

    @Override
    public ExceptionHandler getWrapped() {
        return wrapped;
    }

}

(note that this particular example navigates to viewexpired, so it expects a /viewexpired.xhtml as error page)

The above needs to be baked by the following ExceptionHandlerFactory implementation:

public class ViewExpiredExceptionHandlerFactory extends ExceptionHandlerFactory {

    private ExceptionHandlerFactory parent;

    public ViewExpiredExceptionHandlerFactory(ExceptionHandlerFactory parent) {
        this.parent = parent;
    }

    @Override
    public ExceptionHandler getExceptionHandler() {
        return new ViewExpiredExceptionHandler(parent.getExceptionHandler());
    }

}

which in turn needs to be registered in faces-config.xml as follows:

<factory>
    <exception-handler-factory>com.example.ViewExpiredExceptionHandlerFactory</exception-handler-factory>
</factory>