When a servlet or filter is permanently unavailable, something is wrong * with the it, and it cannot handle * requests until some action is taken. For example, a servlet * might be configured incorrectly, or a filter's state may be corrupted. * The component should log both the error and the corrective action * that is needed. * *
A servlet or filter 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 unavailable
* exceptions in the same way. However, treating temporary unavailability
* effectively makes the servlet container more robust. Specifically,
* the servlet container might block requests to the servlet or filter for a period
* of time suggested by the exception, rather than rejecting them until
* the servlet container restarts.
*
*
* @author Various
* @version $Version$
*
*/
public class UnavailableException
extends ServletException {
private Servlet servlet; // what's unavailable
private boolean permanent; // needs admin action?
private int seconds; // unavailability estimate
/**
*
* @deprecated As of Java Servlet API 2.2, use {@link
* #UnavailableException(String)} instead.
*
* @param servlet the Servlet instance that is
* unavailable
*
* @param msg a String specifying the
* descriptive message
*
*/
public UnavailableException(Servlet servlet, String msg) {
super(msg);
this.servlet = servlet;
permanent = true;
}
/**
* @deprecated As of Java Servlet API 2.2, use {@link
* #UnavailableException(String, int)} instead.
*
* @param seconds an integer specifying the number of seconds
* the servlet expects to be unavailable; if
* zero or negative, indicates that the servlet
* can't make an estimate
*
* @param servlet the Servlet that is unavailable
*
* @param msg a String specifying the descriptive
* message, which can be written to a log file or
* displayed for the user.
*
*/
public UnavailableException(int seconds, Servlet servlet, String msg) {
super(msg);
this.servlet = servlet;
if (seconds <= 0)
this.seconds = -1;
else
this.seconds = seconds;
permanent = false;
}
/**
*
* Constructs a new exception with a descriptive
* message indicating that the servlet is permanently
* unavailable.
*
* @param msg a String specifying the
* descriptive message
*
*/
public UnavailableException(String msg) {
super(msg);
permanent = true;
}
/**
* Constructs a new exception with a descriptive message
* indicating that the servlet is temporarily unavailable
* and giving an estimate of how long it will be unavailable.
*
*
In some cases, the servlet cannot make an estimate. For
* example, the servlet might know that a server it needs is
* not running, but not be able to report how long it will take
* to be restored to functionality. This can be indicated with
* a negative or zero value for the seconds argument.
*
* @param msg a String specifying the
* descriptive message, which can be written
* to a log file or displayed for the user.
*
* @param seconds an integer specifying the number of seconds
* the servlet expects to be unavailable; if
* zero or negative, indicates that the servlet
* can't make an estimate
*
*/
public UnavailableException(String msg, int seconds) {
super(msg);
if (seconds <= 0)
this.seconds = -1;
else
this.seconds = seconds;
permanent = false;
}
/**
*
* Returns a boolean indicating
* whether the servlet is permanently unavailable.
* If so, something is wrong with the servlet, and the
* system administrator must take some corrective action.
*
* @return true if the servlet is
* permanently unavailable; false
* if the servlet is available or temporarily
* unavailable
*
*/
public boolean isPermanent() {
return permanent;
}
/**
* @deprecated As of Java Servlet API 2.2, with no replacement.
*
* Returns the servlet that is reporting its unavailability.
*
* @return the Servlet object that is
* throwing the UnavailableException
*
*/
public Servlet getServlet() {
return servlet;
}
/**
* Returns the number of seconds the servlet expects to
* be temporarily unavailable.
*
*
If this method returns a negative number, the servlet * is permanently unavailable or cannot provide an estimate of * how long it will be unavailable. No effort is * made to correct for the time elapsed since the exception was * first reported. * * @return an integer specifying the number of seconds * the servlet will be temporarily unavailable, * or a negative number if the servlet is permanently * unavailable or cannot make an estimate * */ public int getUnavailableSeconds() { return permanent ? -1 : seconds; } }