jakarta.servlet.UnavailableException Maven / Gradle / Ivy
/*
* 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 jakarta.servlet;
/**
* Defines an exception that a servlet or filter throws to indicate that it is
* permanently or temporarily unavailable.
*
* 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.
*
* 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.
*/
public class UnavailableException extends ServletException {
private static final long serialVersionUID = 1L;
/**
* 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;
/**
* 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);
seconds = 0;
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;
}
/**
* 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;
}
}