/*
* 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
*/
public class UnavailableException extends ServletException {
private static final long serialVersionUID = 1L;
private final Servlet servlet; // what's unavailable
private final boolean permanent; // needs admin action?
private final int seconds; // unavailability estimate
/**
* @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;
}
}