if you have the following URL: HTTP://your_server/your_app/product.jsf?id=777, you access the passing parameter id with the following lines of java code: 
FacesContext fc = FacesContext.getCurrentInstance(); 
String id = (String) fc.getExternalContext().getRequestParameterMap().get("id"); 
From the PAGE, you can access the same parameter using the predefined variable with NAME PARAM. For example, 
<H:outputText value="#{param['id']}" /> 
Note: You have to call the jsf page directly and using the servlet mapping.

if you have the following URL: http://your_server/your_app/product.jsf?id=777, you access the passing parameter id with the following lines of java code: 
FacesContext fc = FacesContext.getCurrentInstance(); 
String id = (String) fc.getExternalContext().getRequestParameterMap().get("id"); 
From the page, you can access the same parameter using the predefined variable with name param. For example, 
<h:outputText value="#{param['id']}" /> 
Note: You have to call the jsf page directly and using the servlet mapping.