validation before rendering page [closed]

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I'm new to JSF and using JSF2 to build a webapp which has several pages. I'm using a session scoped bean to keep some parameters that were set by going through the different pages.

When the session times out (or I redeploy the app) and I go to a specific page then this page is not able to render correctly because some data is missing from the session. At this point I want the home page to 开发者_开发问答be shown.

I want to use this mechanism for all pages. So in general I want to do some validation before rendering a page and direct the user to the home page if the validation fails.

How should I handle this?

---

In this particular case I'd use a simple filter which hooks on JSF requests and checks the presence of the managed bean in the session. The below example assumes the following:

• FacesServlet is definied in web.xml as <servlet-name>facesServlet</servlet-name>
• Your session scoped bean has a managed bean name of yourSessionBean.
• Your home page is located at home.xhtml

---

@WebFilter(servletName="facesServlet")
public class FacesSessionFilter implements Filter {

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
        HttpSession session = request.getSession(false);

        if (!request.getRequestURI().endsWith("/home.xhtml") && (session == null || session.getAttribute("yourSessionBean") == null)) {
            response.sendRedirect(request.getContextPath() + "/home.xhtml"); // Redirect to home page.
        } else {
            chain.doFilter(req, res); // Bean is present in session, so just continue request.
        }
    }

    // Add/generate init() and destroy() with empty bodies.
}

Or if you want to do it more JSF-ish, add a <f:event type="preRenderView"> to the master template.

<f:metadata>
    <f:event type="preRenderView" listener="#{someBean.preRenderView}" />
</f:metadata>

with

@ManagedProperty(value="#{yourSessionBean}")
private YourSessionBean yourSessionBean;

public void preRenderView() {
    if (yourSessionBean.isEmpty()) {
        yourSessionBean.addPage("home");
        FacesContext.getCurrentInstance().getExternalContext().redirect("/home.xhtml");
    }
}