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<TITLE>Servlet::UnavailableException - servlet unavailability exception</TITLE>
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<LI><A HREF="#name">NAME</A></LI>
<LI><A HREF="#synopsis">SYNOPSIS</A></LI>
<LI><A HREF="#description">DESCRIPTION</A></LI>
<LI><A HREF="#methods">METHODS</A></LI>
<LI><A HREF="#see also">SEE ALSO</A></LI>
<LI><A HREF="#author">AUTHOR</A></LI>
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<H1><A NAME="name">NAME</A></H1>
<P>Servlet::UnavailableException - servlet unavailability exception</P>
<P>
<HR>
<H1><A NAME="synopsis">SYNOPSIS</A></H1>
<PRE>
package My::Servlet;</PRE>
<PRE>
use base qw(Servlet::GenericServlet);
use Servlet::UnavailableException ();</PRE>
<PRE>
sub service {</PRE>
<PRE>
# ...</PRE>
<PRE>
Servlet::UnavailableException->throw('db server inaccessible',
seconds => 30);
}</PRE>
<PRE>
package My::ServletContainer;</PRE>
<PRE>
# ...</PRE>
<PRE>
eval {
$servlet->service($request, $response);
};</PRE>
<PRE>
if ($@ && $@->isa('Servlet::UnavailableException')) {
if ($@->isPermanent()) {
$response->sendError(410) # SC_GONE;
$servlet->destroy();
} else {
$response->sendError(503); # SC_SERVICE_UNAVAILABLE
}
};</PRE>
<PRE>
# ...</PRE>
<P>
<HR>
<H1><A NAME="description">DESCRIPTION</A></H1>
<P>Defines an exception that a servlet throws to indicate that it is
permanently or temporarily unavailable.</P>
<P>When a servlet is permanently unavailable, something is wrong with the
servlet, and it cannot handle requests until some action is taken. For
example, the servlet might be configured incorrectly, or its state may
be corrupted. A servlet should log both the error and the corrective
action that is needed.</P>
<P>A servlet is temporarily unavailable if it cannot handle requests
momentarily due to some system-wide problem. For example, a third-tier
server might not be accessible, or there may be insufficient memory or
disk storage to handle requests. A system administrator may need to
take corrective action.</P>
<P>Servlet containers can safely treat both types of unavailabile
exceptions in the same way. However, treating termporary
unavailability effectively makes the servlet container more
robust. Specifically, the servlet container might block requests to
the servlet for a period of time suggested by the servlet, rather than
rejecting them until the servlet container restarts.</P>
<P>Extends <STRONG>Servlet::ServletException</STRONG>. See that class for a description
of inherited methods.</P>
<P>
<HR>
<H1><A NAME="methods">METHODS</A></H1>
<DL>
<DT><STRONG><A NAME="item_new">new($msg, $seconds)</A></STRONG><BR>
<DD>
Constructs a new exception. Optional arguments include an error
message, and an estimate of temporary unavailability in seconds. If
<EM>seconds</EM> is not specified, the indication is that the servlet is
permanently unavailable.
<P><STRONG>Parameters:</STRONG></P>
<DL>
<DT><STRONG><A NAME="item_%24msg"><EM>$msg</EM></A></STRONG><BR>
<DD>
the error message
<P></P>
<DT><STRONG><A NAME="item_%24seconds"><EM>$seconds</EM></A></STRONG><BR>
<DD>
the number of seconds that the servlet will be unavailable
<P></P></DL>
<DT><STRONG><A NAME="item_getUnavailableSeconds"><CODE>getUnavailableSeconds()</CODE></A></STRONG><BR>
<DD>
Returns the number of seconds the servlet expects to be temporarily
unavailable, or -1 if the servlet is permanently unavailable.
<P></P>
<DT><STRONG><A NAME="item_isPermanent"><CODE>isPermanent()</CODE></A></STRONG><BR>
<DD>
Returns a boolean value indicating whether the servlet is permanently
unavailable.
<P></P></DL>
<P>
<HR>
<H1><A NAME="see also">SEE ALSO</A></H1>
<P><A HREF="../../api/Servlet/ServletException.html">the Servlet::ServletException manpage</A></P>
<P>
<HR>
<H1><A NAME="author">AUTHOR</A></H1>
<P>Brian Moseley, <A HREF="mailto:bcm@maz.org">bcm@maz.org</A></P>
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