You can use the errorPage attribute of the page directive 
to have uncaught runtime exceptions automatically forwarded 
to an error processing page.
For example:
redirects the browser to the JSP page error.jsp if an 
uncaught exception is encountered during request 
processing. Within error.jsp, if you indicate that it is an 
error-processing page, via the directive: 
the Throwable object describing the exception may be 
accessed within the error page via the exception implicit 
object. 
Note: You must always use a relative URL as the value for 
the errorPage attribute.

My declarring errorpage attribute in page directive as
<% page errorPage="error.jsp"%>

and when u think that a jsp is supposed be encountered an 
error then <% page isErrorPage="true"%>