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java/javax/servlet/UnavailableException.java

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+/*
+ * 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;
+
+    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;
+    }
+}