Tomcat example source code file (UnavailableException.java)

This example Tomcat source code file (UnavailableException.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Tomcat tags/keywords

servlet, servlet, servletexception, servletexception, string, string, unavailableexception, unavailableexception

The Tomcat UnavailableException.java source code

/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License.  You may obtain a copy of the License at
*
*     http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package javax.servlet;


/**
 * Defines an exception that a servlet or filter throws to indicate
 * that it is permanently or temporarily unavailable. 
 *
 * <p>When a servlet or filter is permanently unavailable, something is wrong
 * with 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.
 *
 * <p>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.
 *
 * <p>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 <code>Servlet instance that is
     *                  unavailable
     *
     * @param msg 	a <code>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 <code>Servlet that is unavailable
     * 
     * @param msg	a <code>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 <code>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.
     * 
     * <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. This can be indicated with
     * a negative or zero value for the <code>seconds argument.
     *
     * @param msg	a <code>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 <code>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		<code>true if the servlet is
     *			permanently unavailable; <code>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 <code>Servlet object that is 
     *			throwing the <code>UnavailableException
     *
     */
     
    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;
    }
}