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: 2006-10-24 21:01:51 -0700 (Tue, 24 Oct 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 }