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