You normally want to use UIViewRoot#getViewId() for this.
String viewId = facesContext.getViewRoot().getViewId();
This is in EL also available as follows:
#{view.viewId}
Exactly this value is reuseable in navigation case outcomes such as <h:link outcome> and <h:button outcome>.
Alternatively, you can also use HttpServletRequest#getRequestURI() to get whatever the enduser is actually seeing in the browser address bar.
String uri = ((HttpServletRequest) externalContext.getRequest()).getRequestURI();
Which is in EL also available as follows:
#{request.requestURI}
Exactly this value is reuseable in <h:outputLink value> or plain <a href>. Note that you can’t use it as navigation case outcome.