unavailableexception.java

JSWDK服务器

/*
 * $Id: UnavailableException.java,v 1.4 1999/04/20 20:37:43 sahmed Exp $
 * 
 * Copyright (c) 1997-1999 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information").  You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 * 
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 * 
 * CopyrightVersion 1.0
 */

package javax.servlet;


/**
 * Defines an exception that a servlet throws to indicate
 * that it is permanently or temporarily unavailable. 
 *
 * <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>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>Servlet engines can safely treat both types of unavailable
 * exceptions in the same way. However, treating temporary unavailability
 * effectively makes the servlet engine more robust. Specifically,
 * the servlet engine might block requests to the servlet for a period
 * of time suggested by the servlet, rather than rejecting them until
 * the servlet engine 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


    /**
     * 
     * Constructs a new exception with a descriptive
     * message indicating that the servlet is permanently
     * unavailable.
     *
     * @param servlet 	the <code>Servlet</code> instance that is unavailable
     *
     * @param msg 	a <code>String</code> specifying the descriptive message
     *
     */

    public UnavailableException (Servlet servlet, String msg) {
	super (msg);
	this.servlet = servlet;
	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.
     * 
     * <p>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. You can indicate that the servlet
     * can't estimate a time by entering a negative or zero value 
     * for the <code>seconds</code> argument. 
     *
     * @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 <code>Servlet</code> that is unavailable
     * 
     * @param msg		a <code>String</code> 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;
    }




    /**
     *
     * Returns a <code>boolean</code> primitive type 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		<code>true</code> if the servlet is
     *			permanently unavailable; <code>false</code>
     *			if the servlet is available or temporarily
     *			unavailable
     *
     */
     
    public boolean isPermanent () {
	return permanent;
    }

  
  
  
    /**
     * Returns the servlet that is reporting its unavailability.
     * 
     * @return		the <code>Servlet</code> object that is 
     *			throwing the <code>UnavailableException</code>
     *
     */
     
    public Servlet getServlet () {
	return servlet;
    }




    /**
     * Returns the number of seconds the servlet expects to 
     * be temporarily unavailable.  
     *
     * <p>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;
    }
}