UnavailableException.java
/*
* 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.
*/
public class UnavailableException extends ServletException {
private static final long serialVersionUID = 1L;
/**
* The Servlet that is unavailable.
*/
private final Servlet servlet;
/**
* Is the issue permanent - i.e. is administrator action required?
*/
private final boolean permanent;
/**
* The estimate of how long the Servlet will be unavailable.
*/
private final int seconds;
/**
* @param servlet the <code>Servlet</code> instance that is unavailable
* @param msg a <code>String</code> specifying the descriptive message
*
* @deprecated As of Java Servlet API 2.2, use {@link #UnavailableException(String)} instead.
*/
@SuppressWarnings("dep-ann")
// Spec API does not use @Deprecated
public UnavailableException(Servlet servlet, String msg) {
super(msg);
this.servlet = servlet;
permanent = true;
this.seconds = 0;
}
/**
* @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.
*
* @deprecated As of Java Servlet API 2.2, use {@link #UnavailableException(String, int)} instead.
*/
@SuppressWarnings("dep-ann")
// Spec API does not use @Deprecated
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</code> specifying the descriptive message
*/
public UnavailableException(String msg) {
super(msg);
seconds = 0;
servlet = null;
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</code> argument.
*
* @param msg a <code>String</code> 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;
}
servlet = null;
permanent = false;
}
/**
* Returns a <code>boolean</code> 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>
*
* @deprecated As of Java Servlet API 2.2, with no replacement.
*/
@SuppressWarnings("dep-ann")
// Spec API does not use @Deprecated
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;
}
}