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17 package javax.servlet;
18
19
20 /**
21 * Defines an exception that a servlet or filter throws to indicate
22 * that it is permanently or temporarily unavailable.
23 *
24 * <p>When a servlet or filter is permanently unavailable, something is wrong
25 * with it, and it cannot handle
26 * requests until some action is taken. For example, a servlet
27 * might be configured incorrectly, or a filter's state may be corrupted.
28 * The component should log both the error and the corrective action
29 * that is needed.
30 *
31 * <p>A servlet or filter is temporarily unavailable if it cannot handle
32 * requests momentarily due to some system-wide problem. For example,
33 * a third-tier server might not be accessible, or there may be
34 * insufficient memory or disk storage to handle requests. A system
35 * administrator may need to take corrective action.
36 *
37 * <p>Servlet containers can safely treat both types of unavailable
38 * exceptions in the same way. However, treating temporary unavailability
39 * effectively makes the servlet container more robust. Specifically,
40 * the servlet container might block requests to the servlet or filter for a period
41 * of time suggested by the exception, rather than rejecting them until
42 * the servlet container restarts.
43 *
44 *
45 * @author Various
46 * @version $Version$
47 *
48 */
49
50 public class UnavailableException
51 extends ServletException {
52
53 private Servlet servlet;
54 private boolean permanent;
55 private int seconds;
56
57 /**
58 *
59 * @deprecated As of Java Servlet API 2.2, use {@link
60 * #UnavailableException(String)} instead.
61 *
62 * @param servlet the <code>Servlet</code> instance that is
63 * unavailable
64 *
65 * @param msg a <code>String</code> specifying the
66 * descriptive message
67 *
68 */
69
70 public UnavailableException(Servlet servlet, String msg) {
71 super(msg);
72 this.servlet = servlet;
73 permanent = true;
74 }
75
76 /**
77 * @deprecated As of Java Servlet API 2.2, use {@link
78 * #UnavailableException(String, int)} instead.
79 *
80 * @param seconds an integer specifying the number of seconds
81 * the servlet expects to be unavailable; if
82 * zero or negative, indicates that the servlet
83 * can't make an estimate
84 *
85 * @param servlet the <code>Servlet</code> that is unavailable
86 *
87 * @param msg a <code>String</code> specifying the descriptive
88 * message, which can be written to a log file or
89 * displayed for the user.
90 *
91 */
92
93 public UnavailableException(int seconds, Servlet servlet, String msg) {
94 super(msg);
95 this.servlet = servlet;
96 if (seconds <= 0)
97 this.seconds = -1;
98 else
99 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 }