javax.servlet
Class UnavailableException

java.lang.Object
  |
  +--java.lang.Throwable
        |
        +--java.lang.Exception
              |
              +--javax.servlet.ServletException
                    |
                    +--javax.servlet.UnavailableException

public class UnavailableException

extends ServletException

This exception indicates that a servlet is unavailable. Servlets may report this exception at any time, and the network service running the servlet should behave appropriately. There are two types of unavailability, and sophisticated services will to deal with these differently:

• Permanent unavailability. The servlet will not be able to handle client requests until some administrative action is taken to correct a servlet problem. For example, the servlet might be misconfigured, or the state of the servlet may be corrupted. Well written servlets will log both the error and the corrective action which an administrator must perform to let the servlet become available.
• Temporary unavailability. The servlet can not handle requests at this moment due to a 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. The problem may be self correcting, such as those due to excessive load, or corrective action may need to be taken by an administrator.

Network services may safely treat both types of exceptions as "permanent", but good treatment of temporary unavailability leads to more robust network services. Specifically, requests to the servlet might be blocked (or otherwise deferred) for a servlet-suggested amount of time, rather than being rejected until the service itself restarts.

See Also:

Serialized Form

Constructor Summary

UnavailableException(int seconds, Servlet servlet, java.lang.String msg)
Constructs a new exception with the specified descriptive message, indicating that the servlet is temporarily unavailable and giving an estimate of how long it will be unavailable.

UnavailableException(Servlet servlet, java.lang.String msg)
Constructs a new exception with the specified descriptive message, indicating that the servlet is permanently unavailable.

Method Summary

Servlet	getServlet() Returns the servlet that is reporting its unavailability.
int	getUnavailableSeconds() Returns the amount of time the servlet expects to be temporarily unavailable.
boolean	isPermanent() Returns true if the servlet is "permanently" unavailable, indicating that the service administrator must take some corrective action to make the servlet be usable.

Methods inherited from class javax.servlet.ServletException

getRootCause

Methods inherited from class java.lang.Throwable

fillInStackTrace, getLocalizedMessage, getMessage, printStackTrace, printStackTrace, printStackTrace, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

UnavailableException

public UnavailableException(Servlet servlet,
                            java.lang.String msg)

Constructs a new exception with the specified descriptive message, indicating that the servlet is permanently unavailable.

Parameters:

servlet - the servlet which is unavailable

msg - the descriptive message

UnavailableException

public UnavailableException(int seconds,
                            Servlet servlet,
                            java.lang.String msg)

Constructs a new exception with the specified descriptive message, indicating that the servlet is temporarily unavailable and giving an estimate of how long it will be unavailable. In some cases, no estimate can be made; this is indicated by a non-positive time. For example, the servlet might know a server it needs is "down", but not be able to report how long it will take to restore it to an adequate level of functionality.

Parameters:

seconds - number of seconds that the servlet is anticipated to be unavailable. If negative or zero, no estimate is available.

servlet - the servlet which is unavailable

msg - the descriptive message

Method Detail

isPermanent

public boolean isPermanent()

Returns true if the servlet is "permanently" unavailable, indicating that the service administrator must take some corrective action to make the servlet be usable.

getServlet

public Servlet getServlet()

Returns the servlet that is reporting its unavailability.

getUnavailableSeconds

public int getUnavailableSeconds()

Returns the amount of time the servlet expects to be temporarily unavailable. If the servlet is permanently unavailable, or no estimate was provided, returns a negative number. No effort is made to correct for the time elapsed since the exception was first reported.