1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 */
19
20 package javax.servlet;
21
22 import java.io.IOException;
23
24
25 /**
26 * Defines methods that all servlets must implement.
27 *
28 * <p>A servlet is a small Java program that runs within a Web server.
29 * Servlets receive and respond to requests from Web clients,
30 * usually across HTTP, the HyperText Transfer Protocol.
31 *
32 * <p>To implement this interface, you can write a generic servlet
33 * that extends
34 * <code>javax.servlet.GenericServlet</code> or an HTTP servlet that
35 * extends <code>javax.servlet.http.HttpServlet</code>.
36 *
37 * <p>This interface defines methods to initialize a servlet,
38 * to service requests, and to remove a servlet from the server.
39 * These are known as life-cycle methods and are called in the
40 * following sequence:
41 * <ol>
42 * <li>The servlet is constructed, then initialized with the <code>init</code> method.
43 * <li>Any calls from clients to the <code>service</code> method are handled.
44 * <li>The servlet is taken out of service, then destroyed with the
45 * <code>destroy</code> method, then garbage collected and finalized.
46 * </ol>
47 *
48 * <p>In addition to the life-cycle methods, this interface
49 * provides the <code>getServletConfig</code> method, which the servlet
50 * can use to get any startup information, and the <code>getServletInfo</code>
51 * method, which allows the servlet to return basic information about itself,
52 * such as author, version, and copyright.
53 *
54 * @author Various
55 * @version $Version$
56 *
57 * @see GenericServlet
58 * @see javax.servlet.http.HttpServlet
59 *
60 */
61
62
63 public interface Servlet {
64
65 /**
66 * Called by the servlet container to indicate to a servlet that the
67 * servlet is being placed into service.
68 *
69 * <p>The servlet container calls the <code>init</code>
70 * method exactly once after instantiating the servlet.
71 * The <code>init</code> method must complete successfully
72 * before the servlet can receive any requests.
73 *
74 * <p>The servlet container cannot place the servlet into service
75 * if the <code>init</code> method
76 * <ol>
77 * <li>Throws a <code>ServletException</code>
78 * <li>Does not return within a time period defined by the Web server
79 * </ol>
80 *
81 *
82 * @param config a <code>ServletConfig</code> object
83 * containing the servlet's
84 * configuration and initialization parameters
85 *
86 * @exception ServletException if an exception has occurred that
87 * interferes with the servlet's normal
88 * operation
89 *
90 * @see UnavailableException
91 * @see #getServletConfig
92 *
93 */
94
95 public void init(ServletConfig config) throws ServletException;
96
97
98
99 /**
100 *
101 * Returns a {@link ServletConfig} object, which contains
102 * initialization and startup parameters for this servlet.
103 * The <code>ServletConfig</code> object returned is the one
104 * passed to the <code>init</code> method.
105 *
106 * <p>Implementations of this interface are responsible for storing the
107 * <code>ServletConfig</code> object so that this
108 * method can return it. The {@link GenericServlet}
109 * class, which implements this interface, already does this.
110 *
111 * @return the <code>ServletConfig</code> object
112 * that initializes this servlet
113 *
114 * @see #init
115 *
116 */
117
118 public ServletConfig getServletConfig();
119
120
121
122 /**
123 * Called by the servlet container to allow the servlet to respond to
124 * a request.
125 *
126 * <p>This method is only called after the servlet's <code>init()</code>
127 * method has completed successfully.
128 *
129 * <p> The status code of the response always should be set for a servlet
130 * that throws or sends an error.
131 *
132 *
133 * <p>Servlets typically run inside multithreaded servlet containers
134 * that can handle multiple requests concurrently. Developers must
135 * be aware to synchronize access to any shared resources such as files,
136 * network connections, and as well as the servlet's class and instance
137 * variables.
138 * More information on multithreaded programming in Java is available in
139 * <a href="http://java.sun.com/Series/Tutorial/java/threads/multithreaded.html">
140 * the Java tutorial on multi-threaded programming</a>.
141 *
142 *
143 * @param req the <code>ServletRequest</code> object that contains
144 * the client's request
145 *
146 * @param res the <code>ServletResponse</code> object that contains
147 * the servlet's response
148 *
149 * @exception ServletException if an exception occurs that interferes
150 * with the servlet's normal operation
151 *
152 * @exception IOException if an input or output exception occurs
153 *
154 */
155
156 public void service(ServletRequest req, ServletResponse res)
157 throws ServletException, IOException;
158
159
160
161 /**
162 * Returns information about the servlet, such
163 * as author, version, and copyright.
164 *
165 * <p>The string that this method returns should
166 * be plain text and not markup of any kind (such as HTML, XML,
167 * etc.).
168 *
169 * @return a <code>String</code> containing servlet information
170 *
171 */
172
173 public String getServletInfo();
174
175
176
177 /**
178 *
179 * Called by the servlet container to indicate to a servlet that the
180 * servlet is being taken out of service. This method is
181 * only called once all threads within the servlet's
182 * <code>service</code> method have exited or after a timeout
183 * period has passed. After the servlet container calls this
184 * method, it will not call the <code>service</code> method again
185 * on this servlet.
186 *
187 * <p>This method gives the servlet an opportunity
188 * to clean up any resources that are being held (for example, memory,
189 * file handles, threads) and make sure that any persistent state is
190 * synchronized with the servlet's current state in memory.
191 *
192 */
193
194 public void destroy();
195 }