001 /*
002 * Copyright 2004 The Apache Software Foundation
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package javax.servlet;
018
019
020 /**
021 * Defines an exception that a servlet or filter throws to indicate
022 * that it is permanently or temporarily unavailable.
023 *
024 * <p>When a servlet or filter is permanently unavailable, something is wrong
025 * with it, and it cannot handle
026 * requests until some action is taken. For example, a servlet
027 * might be configured incorrectly, or a filter's state may be corrupted.
028 * The component should log both the error and the corrective action
029 * that is needed.
030 *
031 * <p>A servlet or filter is temporarily unavailable if it cannot handle
032 * requests momentarily due to some system-wide problem. For example,
033 * a third-tier server might not be accessible, or there may be
034 * insufficient memory or disk storage to handle requests. A system
035 * administrator may need to take corrective action.
036 *
037 * <p>Servlet containers can safely treat both types of unavailable
038 * exceptions in the same way. However, treating temporary unavailability
039 * effectively makes the servlet container more robust. Specifically,
040 * the servlet container might block requests to the servlet or filter for a period
041 * of time suggested by the exception, rather than rejecting them until
042 * the servlet container restarts.
043 *
044 *
045 * @author Various
046 * @version $Version$
047 *
048 */
049
050 public class UnavailableException
051 extends ServletException {
052
053 private Servlet servlet; // what's unavailable
054 private boolean permanent; // needs admin action?
055 private int seconds; // unavailability estimate
056
057 /**
058 *
059 * @deprecated As of Java Servlet API 2.2, use {@link
060 * #UnavailableException(String)} instead.
061 *
062 * @param servlet the <code>Servlet</code> instance that is
063 * unavailable
064 *
065 * @param msg a <code>String</code> specifying the
066 * descriptive message
067 *
068 */
069
070 public UnavailableException(Servlet servlet, String msg) {
071 super(msg);
072 this.servlet = servlet;
073 permanent = true;
074 }
075
076 /**
077 * @deprecated As of Java Servlet API 2.2, use {@link
078 * #UnavailableException(String, int)} instead.
079 *
080 * @param seconds an integer specifying the number of seconds
081 * the servlet expects to be unavailable; if
082 * zero or negative, indicates that the servlet
083 * can't make an estimate
084 *
085 * @param servlet the <code>Servlet</code> that is unavailable
086 *
087 * @param msg a <code>String</code> specifying the descriptive
088 * message, which can be written to a log file or
089 * displayed for the user.
090 *
091 */
092
093 public UnavailableException(int seconds, Servlet servlet, String msg) {
094 super(msg);
095 this.servlet = servlet;
096 if (seconds <= 0)
097 this.seconds = -1;
098 else
099 this.seconds = seconds;
100 permanent = false;
101 }
102
103 /**
104 *
105 * Constructs a new exception with a descriptive
106 * message indicating that the servlet is permanently
107 * unavailable.
108 *
109 * @param msg a <code>String</code> specifying the
110 * descriptive message
111 *
112 */
113
114 public UnavailableException(String msg) {
115 super(msg);
116
117 permanent = true;
118 }
119
120 /**
121 * Constructs a new exception with a descriptive message
122 * indicating that the servlet is temporarily unavailable
123 * and giving an estimate of how long it will be unavailable.
124 *
125 * <p>In some cases, the servlet cannot make an estimate. For
126 * example, the servlet might know that a server it needs is
127 * not running, but not be able to report how long it will take
128 * to be restored to functionality. This can be indicated with
129 * a negative or zero value for the <code>seconds</code> argument.
130 *
131 * @param msg a <code>String</code> specifying the
132 * descriptive message, which can be written
133 * to a log file or displayed for the user.
134 *
135 * @param seconds an integer specifying the number of seconds
136 * the servlet expects to be unavailable; if
137 * zero or negative, indicates that the servlet
138 * can't make an estimate
139 *
140 */
141
142 public UnavailableException(String msg, int seconds) {
143 super(msg);
144
145 if (seconds <= 0)
146 this.seconds = -1;
147 else
148 this.seconds = seconds;
149
150 permanent = false;
151 }
152
153 /**
154 *
155 * Returns a <code>boolean</code> indicating
156 * whether the servlet is permanently unavailable.
157 * If so, something is wrong with the servlet, and the
158 * system administrator must take some corrective action.
159 *
160 * @return <code>true</code> if the servlet is
161 * permanently unavailable; <code>false</code>
162 * if the servlet is available or temporarily
163 * unavailable
164 *
165 */
166
167 public boolean isPermanent() {
168 return permanent;
169 }
170
171 /**
172 * @deprecated As of Java Servlet API 2.2, with no replacement.
173 *
174 * Returns the servlet that is reporting its unavailability.
175 *
176 * @return the <code>Servlet</code> object that is
177 * throwing the <code>UnavailableException</code>
178 *
179 */
180
181 public Servlet getServlet() {
182 return servlet;
183 }
184
185 /**
186 * Returns the number of seconds the servlet expects to
187 * be temporarily unavailable.
188 *
189 * <p>If this method returns a negative number, the servlet
190 * is permanently unavailable or cannot provide an estimate of
191 * how long it will be unavailable. No effort is
192 * made to correct for the time elapsed since the exception was
193 * first reported.
194 *
195 * @return an integer specifying the number of seconds
196 * the servlet will be temporarily unavailable,
197 * or a negative number if the servlet is permanently
198 * unavailable or cannot make an estimate
199 *
200 */
201
202 public int getUnavailableSeconds() {
203 return permanent ? -1 : seconds;
204 }
205 }