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 import java.io.IOException;
020
021
022 /**
023 * Defines methods that all servlets must implement.
024 *
025 * <p>A servlet is a small Java program that runs within a Web server.
026 * Servlets receive and respond to requests from Web clients,
027 * usually across HTTP, the HyperText Transfer Protocol.
028 *
029 * <p>To implement this interface, you can write a generic servlet
030 * that extends
031 * <code>javax.servlet.GenericServlet</code> or an HTTP servlet that
032 * extends <code>javax.servlet.http.HttpServlet</code>.
033 *
034 * <p>This interface defines methods to initialize a servlet,
035 * to service requests, and to remove a servlet from the server.
036 * These are known as life-cycle methods and are called in the
037 * following sequence:
038 * <ol>
039 * <li>The servlet is constructed, then initialized with the <code>init</code> method.
040 * <li>Any calls from clients to the <code>service</code> method are handled.
041 * <li>The servlet is taken out of service, then destroyed with the
042 * <code>destroy</code> method, then garbage collected and finalized.
043 * </ol>
044 *
045 * <p>In addition to the life-cycle methods, this interface
046 * provides the <code>getServletConfig</code> method, which the servlet
047 * can use to get any startup information, and the <code>getServletInfo</code>
048 * method, which allows the servlet to return basic information about itself,
049 * such as author, version, and copyright.
050 *
051 * @author Various
052 * @version $Version$
053 *
054 * @see GenericServlet
055 * @see javax.servlet.http.HttpServlet
056 *
057 */
058
059
060 public interface Servlet {
061
062 /**
063 * Called by the servlet container to indicate to a servlet that the
064 * servlet is being placed into service.
065 *
066 * <p>The servlet container calls the <code>init</code>
067 * method exactly once after instantiating the servlet.
068 * The <code>init</code> method must complete successfully
069 * before the servlet can receive any requests.
070 *
071 * <p>The servlet container cannot place the servlet into service
072 * if the <code>init</code> method
073 * <ol>
074 * <li>Throws a <code>ServletException</code>
075 * <li>Does not return within a time period defined by the Web server
076 * </ol>
077 *
078 *
079 * @param config a <code>ServletConfig</code> object
080 * containing the servlet's
081 * configuration and initialization parameters
082 *
083 * @exception ServletException if an exception has occurred that
084 * interferes with the servlet's normal
085 * operation
086 *
087 * @see UnavailableException
088 * @see #getServletConfig
089 *
090 */
091
092 public void init(ServletConfig config) throws ServletException;
093
094
095
096 /**
097 *
098 * Returns a {@link ServletConfig} object, which contains
099 * initialization and startup parameters for this servlet.
100 * The <code>ServletConfig</code> object returned is the one
101 * passed to the <code>init</code> method.
102 *
103 * <p>Implementations of this interface are responsible for storing the
104 * <code>ServletConfig</code> object so that this
105 * method can return it. The {@link GenericServlet}
106 * class, which implements this interface, already does this.
107 *
108 * @return the <code>ServletConfig</code> object
109 * that initializes this servlet
110 *
111 * @see #init
112 *
113 */
114
115 public ServletConfig getServletConfig();
116
117
118
119 /**
120 * Called by the servlet container to allow the servlet to respond to
121 * a request.
122 *
123 * <p>This method is only called after the servlet's <code>init()</code>
124 * method has completed successfully.
125 *
126 * <p> The status code of the response always should be set for a servlet
127 * that throws or sends an error.
128 *
129 *
130 * <p>Servlets typically run inside multithreaded servlet containers
131 * that can handle multiple requests concurrently. Developers must
132 * be aware to synchronize access to any shared resources such as files,
133 * network connections, and as well as the servlet's class and instance
134 * variables.
135 * More information on multithreaded programming in Java is available in
136 * <a href="http://java.sun.com/Series/Tutorial/java/threads/multithreaded.html">
137 * the Java tutorial on multi-threaded programming</a>.
138 *
139 *
140 * @param req the <code>ServletRequest</code> object that contains
141 * the client's request
142 *
143 * @param res the <code>ServletResponse</code> object that contains
144 * the servlet's response
145 *
146 * @exception ServletException if an exception occurs that interferes
147 * with the servlet's normal operation
148 *
149 * @exception IOException if an input or output exception occurs
150 *
151 */
152
153 public void service(ServletRequest req, ServletResponse res)
154 throws ServletException, IOException;
155
156
157
158 /**
159 * Returns information about the servlet, such
160 * as author, version, and copyright.
161 *
162 * <p>The string that this method returns should
163 * be plain text and not markup of any kind (such as HTML, XML,
164 * etc.).
165 *
166 * @return a <code>String</code> containing servlet information
167 *
168 */
169
170 public String getServletInfo();
171
172
173
174 /**
175 *
176 * Called by the servlet container to indicate to a servlet that the
177 * servlet is being taken out of service. This method is
178 * only called once all threads within the servlet's
179 * <code>service</code> method have exited or after a timeout
180 * period has passed. After the servlet container calls this
181 * method, it will not call the <code>service</code> method again
182 * on this servlet.
183 *
184 * <p>This method gives the servlet an opportunity
185 * to clean up any resources that are being held (for example, memory,
186 * file handles, threads) and make sure that any persistent state is
187 * synchronized with the servlet's current state in memory.
188 *
189 */
190
191 public void destroy();
192 }