001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *  http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing,
013     * software distributed under the License is distributed on an
014     * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015     * KIND, either express or implied.  See the License for the
016     * specific language governing permissions and limitations
017     * under the License.
018     */
019    
020    //
021    // This source code implements specifications defined by the Java
022    // Community Process. In order to remain compliant with the specification
023    // DO NOT add / change / or delete method signatures!
024    //
025    
026    package javax.servlet;
027    
028    import java.io.IOException;
029    
030    /**
031     * Defines methods that all servlets must implement.
032     *
033     * <p>A servlet is a small Java program that runs within a Web server.
034     * Servlets receive and respond to requests from Web clients,
035     * usually across HTTP, the HyperText Transfer Protocol.
036     *
037     * <p>To implement this interface, you can write a generic servlet
038     * that extends
039     * <code>javax.servlet.GenericServlet</code> or an HTTP servlet that
040     * extends <code>javax.servlet.http.HttpServlet</code>.
041     *
042     * <p>This interface defines methods to initialize a servlet,
043     * to service requests, and to remove a servlet from the server.
044     * These are known as life-cycle methods and are called in the
045     * following sequence:
046     * <ol>
047     * <li>The servlet is constructed, then initialized with the <code>init</code> method.
048     * <li>Any calls from clients to the <code>service</code> method are handled.
049     * <li>The servlet is taken out of service, then destroyed with the
050     * <code>destroy</code> method, then garbage collected and finalized.
051     * </ol>
052     *
053     * <p>In addition to the life-cycle methods, this interface
054     * provides the <code>getServletConfig</code> method, which the servlet
055     * can use to get any startup information, and the <code>getServletInfo</code>
056     * method, which allows the servlet to return basic information about itself,
057     * such as author, version, and copyright.
058     *
059     * @see GenericServlet
060     * @see javax.servlet.http.HttpServlet
061     *
062     * @version $Rev: 467553 $ $Date: 2006-10-25 06:01:51 +0200 (Mi, 25. Okt 2006) $
063     */
064    public interface Servlet {
065        /**
066         * Called by the servlet container to indicate to a servlet that the
067         * servlet is being placed into service.
068         *
069         * <p>The servlet container calls the <code>init</code>
070         * method exactly once after instantiating the servlet.
071         * The <code>init</code> method must complete successfully
072         * before the servlet can receive any requests.
073         *
074         * <p>The servlet container cannot place the servlet into service
075         * if the <code>init</code> method
076         * <ol>
077         * <li>Throws a <code>ServletException</code>
078         * <li>Does not return within a time period defined by the Web server
079         * </ol>
080         *
081         *
082         * @param config a <code>ServletConfig</code> object
083         * containing the servlet's configuration and initialization parameters
084         *
085         * @exception ServletException if an exception has occurred that
086         * interferes with the servlet's normal operation
087         *
088         * @see UnavailableException
089         * @see #getServletConfig
090         */
091        public void init(ServletConfig config) throws ServletException;
092    
093        /**
094         * Returns a {@link ServletConfig} object, which contains
095         * initialization and startup parameters for this servlet.
096         * The <code>ServletConfig</code> object returned is the one
097         * passed to the <code>init</code> method.
098         *
099         * <p>Implementations of this interface are responsible for storing the
100         * <code>ServletConfig</code> object so that this
101         * method can return it. The {@link GenericServlet}
102         * class, which implements this interface, already does this.
103         *
104         * @return the <code>ServletConfig</code> object
105         * that initializes this servlet
106         *
107         * @see #init
108         */
109        public ServletConfig getServletConfig();
110    
111        /**
112         * Called by the servlet container to allow the servlet to respond to
113         * a request.
114         *
115         * <p>This method is only called after the servlet's <code>init()</code>
116         * method has completed successfully.
117         *
118         * <p>  The status code of the response always should be set for a servlet
119         * that throws or sends an error.
120         *
121         * <p>Servlets typically run inside multithreaded servlet containers
122         * that can handle multiple requests concurrently. Developers must
123         * be aware to synchronize access to any shared resources such as files,
124         * network connections, and as well as the servlet's class and instance
125         * variables.
126         * More information on multithreaded programming in Java is available in
127         * <a href="http://java.sun.com/Series/Tutorial/java/threads/multithreaded.html">
128         * the Java tutorial on multi-threaded programming</a>.
129         *
130         *
131         * @param req the <code>ServletRequest</code> object that contains
132         * the client's request
133         *
134         * @param res the <code>ServletResponse</code> object that contains
135         * the servlet's response
136         *
137         * @exception ServletException if an exception occurs that interferes
138         * with the servlet's normal operation
139         *
140         * @exception IOException if an input or output exception occurs
141         */
142        public void service(ServletRequest req, ServletResponse res)
143                throws ServletException, IOException;
144    
145        /**
146         * Returns information about the servlet, such
147         * as author, version, and copyright.
148         *
149         * <p>The string that this method returns should
150         * be plain text and not markup of any kind (such as HTML, XML,
151         * etc.).
152         *
153         * @return a <code>String</code> containing servlet information
154         */
155        public String getServletInfo();
156    
157        /**
158         * Called by the servlet container to indicate to a servlet that the
159         * servlet is being taken out of service.  This method is
160         * only called once all threads within the servlet's
161         * <code>service</code> method have exited or after a timeout
162         * period has passed. After the servlet container calls this
163         * method, it will not call the <code>service</code> method again
164         * on this servlet.
165         *
166         * <p>This method gives the servlet an opportunity
167         * to clean up any resources that are being held (for example, memory,
168         * file handles, threads) and make sure that any persistent state is
169         * synchronized with the servlet's current state in memory.
170         */
171        public void destroy();
172    }