What is the difference between redirect and navigation/forward and when to use what?

What is difference between a navigation in JSF

FacesContext context = FacesContext.getCurrentInstance();
context.getApplication().getNavigationHandler().handleNavigation(context, null, url);

and a redirect

HttpServletResponse response = (HttpServletResponse) FacesContext.getCurrentInstance().getExternalContext().getResponse();
response.sendRedirect(url);

and how to decide when to use what?

The issue with navigation is that page URL does not change unless faces-redirect=true is added to the query string of the navigation URL. However, in my case appending faces-redirect=true throws error if I want to redirect to a non-JSF page like a plain HTML page.

And another option is as BalusC suggested at JSF 2.0 redirect error

First of all, the term "redirect" is in web development world the action of sending the client an empty HTTP response with just a Location header with therein the new URL on which the client has to send a brand new GET request. So basically:

• Client sends a HTTP request to somepage.xhtml.
• Server sends a HTTP response back with Location: newpage.xhtml header
• Client sends a HTTP request to newpage.xhtml (this get reflected in browser address bar!)
• Server sends a HTTP response back with content of newpage.xhtml.

You can track it with the webbrowser's builtin/addon developer toolset. Press F12 in Chrome/IE9/Firebug and check the "Network" section to see it.

The JSF navigationhandler doesn't send a redirect. Instead, it uses the content of the target page as HTTP response.

• Client sends a HTTP request to somepage.xhtml.
• Server sends a HTTP response back with content of newpage.xhtml.

However as the original HTTP request was to somepage.xhtml, the URL in browser address bar remains unchanged. If you are familiar with the basic Servlet API, then you should understand that this has the same effect as RequestDispatcher#forward().

As to whether pulling the HttpServletResponse from under the JSF hoods and calling sendRedirect() on it is the proper usage; no, that isn't the proper usage. Your server logs will get cluttered with IllegalStateExceptions because this way you aren't telling JSF that you've already taken over the control of the response handling and thus JSF shouldn't do its default response handling job. You should in fact be executing FacesContext#responseComplete() afterwards.

Also, everytime whenever you need to import something from javax.servlet.* package in a JSF artifact like a managed bean, you should absolutely stop writing code and think twice if you're really doing things the right way and ask yourself if there isn't already a "standard JSF way" for whatever you're trying to achieve and/or if the task really belongs in a JSF managed bean (there are namely some cases wherein a simple servlet filter would have been a better place).

The proper way of performing a redirect in JSF is using faces-redirect=true query string in the action outcome:

public String submit() {
    // ...
    return "/newpage.xhtml?faces-redirect=true";
}

Or using ExternalContext#redirect() when you're not inside an action method such as an ajax or prerender listener method:

public void listener() throws IOException {
    // ...
    ExternalContext ec = FacesContext.getCurrentInstance().getExternalContext();
    ec.redirect(ec.getRequestContextPath() + "/newpage.xhtml");
}

(yes, you do not need to put a try-catch around it on IOException, just let the exception go through throws, the servletcontainer will handle it)

Or using NavigationHandler#handleNavigation() in specific cases if you're using XML navigation cases and/or a custom navigation handler with some builtin listener:

public void listener() {
    // ...
    FacesContext fc = FacesContext.getCurrentInstance();
    NavigationHandler nh = fc.getApplication().getNavigationHandler();
    nh.handleNavigation(fc, null, "/newpage.xhtml?faces-redirect=true");
}

As to why the navigation handler fails for "plain HTML" files, that is simply because the navigation handler can process JSF views only, not other files. You should be using ExternalContext#redirect() then.

See also:

• How to navigate in JSF? How to make URL reflect current page (and not previous one)
• When should I use h:outputLink instead of h:commandLink?