JSP is a Java view technology running on the server machine which allows you to write template text in client side languages (like HTML, CSS, JavaScript, ect.). JSP supports taglibs, which are backed by pieces of Java code that let you control the page flow or output dynamically. A well-known taglib is JSTL. JSP also supports Expression Language, which can be used to access backend data (via attributes available in the page, request, session and application scopes), mostly in combination with taglibs.
When a JSP is requested for the first time or when the web app starts up, the servlet container will compile it into a class extending HttpServlet
and use it during the web app's lifetime. You can find the generated source code in the server's work directory. In for example Tomcat, it's the /work
directory. On a JSP request, the servlet container will execute the compiled JSP class and send the generated output (usually just HTML/CSS/JS) through the web server over a network to the client side, which in turn displays it in the web browser.
Servlet is a Java application programming interface (API) running on the server machine, which intercepts requests made by the client and generates/sends a response. A well-known example is the HttpServlet
which provides methods to hook on HTTP requests using the popular HTTP methods such as GET
and POST
. You can configure HttpServlet
s to listen to a certain HTTP URL pattern, which is configurable in web.xml
, or more recently with Java EE 6, with @WebServlet
annotation.
When a Servlet is first requested or during web app startup, the servlet container will create an instance of it and keep it in memory during the web app's lifetime. The same instance will be reused for every incoming request whose URL matches the servlet's URL pattern. You can access the request data by HttpServletRequest
and handle the response by HttpServletResponse
. Both objects are available as method arguments inside any of the overridden methods of HttpServlet
, such as doGet()
and doPost()
.
JSF is a component based MVC framework which is built on top of the Servlet API and provides components via taglibs which can be used in JSP or any other Java based view technology such as Facelets. Facelets is much more suited to JSF than JSP. It namely provides great templating capabilities such as composite components, while JSP basically only offers the <jsp:include>
for templating in JSF, so that you're forced to create custom components with raw Java code (which is a bit opaque and a lot of tedious work) when you want to replace a repeated group of components with a single component. Since JSF 2.0, JSP has been deprecated as view technology in favor of Facelets.
Note: JSP itself is NOT deprecated, just the combination of JSF with JSP is deprecated.
Note: JSP has great templating abilities by means of Taglibs, especially the (Tag File) variant. JSP templating in combination with JSF is what is lacking.
As being a MVC (Model-View-Controller) framework, JSF provides the FacesServlet
as the sole request-response Controller. It takes all the standard and tedious HTTP request/response work from your hands, such as gathering user input, validating/converting them, putting them in model objects, invoking actions and rendering the response. This way you end up with basically a JSP or Facelets (XHTML) page for View and a JavaBean class as Model. The JSF components are used to bind the view with the model (such as your ASP.NET web control does) and the FacesServlet
uses the JSF component tree to do all the work.
Related questions
This test case is bogus. The ViewExpiredException
is usually only thrown during restoring the view (because it's missing in the session), not during rendering the response nor instantiating the bean. In your case this exception is thrown during instantiating the bean and this exception is been wrapped in a ServletException
.
The real ViewExpiredException
is usually only thrown when you send a HTTP POST request to the server while the HTTP session is expired. So there are basically two ways to reproduce this reliably:
Open a JSF page with a POST form (h:form
is by default already POST) in a webbrowser, shutdown the server and clean its work directory (important, because most servers will serialize open sessions to disk on shutdown and unserialize them on startup), restart the server and submit the already opened form. A ViewExpiredException
will be thrown.
Set the <session-timeout>
in web.xml
to 1
minute and submit the form over 1 minute after opening the JSF page with the POST form. This will throw the ViewExpiredException
as well.
Best Answer
To handle the exception whenever the user invokes a synchronous POST request on a page while the HTTP session has been expired and the JSF view state saving method is set to
server
, add an<error-page>
to theweb.xml
which catches the JSFViewExpiredException
and shows the home page.To handle the exception on asynchronous (ajax) requests as well, you need to implement a custom
ExceptionHandler
as answered in Session timeout and ViewExpiredException handling on JSF/PrimeFaces ajax requestSee also: