NAME

Servlet::UnavailableException - servlet unavailability exception

SYNOPSIS

  package My::Servlet;

  use base qw(Servlet::GenericServlet);
  use Servlet::UnavailableException ();

  sub service {

      # ...

      Servlet::UnavailableException->throw('db server inaccessible',
                                           seconds => 30);
  }

  package My::ServletContainer;

  # ...

  eval {
      $servlet->service($request, $response);
  };

  if ($@ && $@->isa('Servlet::UnavailableException')) {
      if ($@->isPermanent()) {
          $response->sendError(410) # SC_GONE;
          $servlet->destroy();
      } else {
          $response->sendError(503); # SC_SERVICE_UNAVAILABLE
      }
  };

  # ...

DESCRIPTION

Defines an exception that a servlet throws to indicate that it is permanently or temporarily unavailable.

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.

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.

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.

Extends Servlet::ServletException. See that class for a description of inherited methods.

METHODS

new($msg, $seconds)

Constructs a new exception. Optional arguments include an error message, and an estimate of temporary unavailability in seconds. If seconds is not specified, the indication is that the servlet is permanently unavailable.

Parameters:

$msg

the error message

$seconds

the number of seconds that the servlet will be unavailable

getUnavailableSeconds()

Returns the number of seconds the servlet expects to be temporarily unavailable, or -1 if the servlet is permanently unavailable.

isPermanent()

Returns a boolean value indicating whether the servlet is permanently unavailable.

SEE ALSO

Servlet::ServletException

AUTHOR

Brian Moseley, bcm@maz.org