ViewExpiredException shown in java.lang.Throwable error-page in web.xml

问题

I'm working on a JSF web application in which I need to bring up a "Session Expired" page if the view expires, but a general technical error page for all others. The application only goes to the technical error page when I trigger the exception. Here's the error-page definitions:

<error-page> 
    <exception-type>javax.faces.application.ViewExpiredException</exception-type> 
    <location>/jsps/utility/sessionExpired.jsp</location> 
</error-page> 
<error-page> 
    <exception-type>java.lang.Throwable</exception-type> 
    <location>/jsps/utility/technicalError.jsp</location> 
</error-page> 
<error-page>
    <error-code>500</error-code>
    <location>/jsps/utility/technicalError.jsp</location>
</error-page>

I removed the technicalError.jsp error page elements and it worked fine, but when I put them back I can't get to the sessionExpired.jsp page. How do I tell the web container the order to evaluate these tags so that the right page comes up? Thanks.

回答1:

This is because the ViewExpiredException is been wrapped in a ServletException as per the JSF specification. Here's an extract of chapter 10.2.6.2 of the JSF 1.2 specification:

10.2.6.2 FacesServlet

Call the execute() method of the saved Lifecycle instance, passing the FacesContext instance for this request as a parameter. If the execute() method throws a FacesException, re-throw it as a ServletException with the FacesException as the root cause.

How the error pages are allocated is specified in Servlet API specification. Here's an extract of chapter 9.9.2 of Servlet API specification 2.5:

SRV.9.9.2 Error Pages

If no error-page declaration containing an exception-type fits using the class-hierarchy match, and the exception thrown is a ServletException or subclass thereof, the container extracts the wrapped exception, as defined by the ServletException.getRootCause method. A second pass is made over the error page declarations, again attempting the match against the error page declarations, but using the wrapped exception instead.

In class hierarchy, ServletException already matches Throwable, so its root cause won't be extracted for the second pass.

To prove this specified behaviour, replace javax.faces.application.ViewExpiredException by javax.servlet.ServletException as <exception-type> and retry. You'll see the expected error page being displayed.

To solve this, simply remove the error page on java.lang.Throwable or java.lang.Exception. If no one exception specific error page matches, then it will fall back to the one for error code of 500 anyway. So, all you need is this:

<error-page> 
    <exception-type>javax.faces.application.ViewExpiredException</exception-type> 
    <location>/jsps/utility/sessionExpired.jsp</location> 
</error-page> 
<error-page>
    <error-code>500</error-code>
    <location>/jsps/utility/technicalError.jsp</location>
</error-page>

---

Update: as per the (deleted) comment of the OP: to reliably test this you cannot do a throw new ViewExpiredException() in a bean constructor or method or so. It would in turn get wrapped in some EL exception. You can eventually add a debug line printing rootCause in the Filter to see it yourself.

If you're using Eclipse/Tomcat, a quick way to test ViewExpiredException is the following:

1. Create a JSF page with a simple command button, deploy and run it and open it in webbrowser.
2. Go back to Eclipse, rightclick Tomcat server and choose Clean Tomcat Work Directory. This will restart Tomcat and trash all serialized sessions (important! just restarting Tomcat is not enough).
3. Go back to webbrowser and press the command button (without reloading page beforehand!).

来源：https://stackoverflow.com/questions/3206922/viewexpiredexception-shown-in-java-lang-throwable-error-page-in-web-xml