1 /**
2 *
3 * Copyright 2003-2004 The Apache Software Foundation
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * 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
19
20
21
22
23
24 package javax.servlet;
25
26 import java.io.IOException;
27
28 /**
29 * Defines methods that all servlets must implement.
30 *
31 * <p>A servlet is a small Java program that runs within a Web server.
32 * Servlets receive and respond to requests from Web clients,
33 * usually across HTTP, the HyperText Transfer Protocol.
34 *
35 * <p>To implement this interface, you can write a generic servlet
36 * that extends
37 * <code>javax.servlet.GenericServlet</code> or an HTTP servlet that
38 * extends <code>javax.servlet.http.HttpServlet</code>.
39 *
40 * <p>This interface defines methods to initialize a servlet,
41 * to service requests, and to remove a servlet from the server.
42 * These are known as life-cycle methods and are called in the
43 * following sequence:
44 * <ol>
45 * <li>The servlet is constructed, then initialized with the <code>init</code> method.
46 * <li>Any calls from clients to the <code>service</code> method are handled.
47 * <li>The servlet is taken out of service, then destroyed with the
48 * <code>destroy</code> method, then garbage collected and finalized.
49 * </ol>
50 *
51 * <p>In addition to the life-cycle methods, this interface
52 * provides the <code>getServletConfig</code> method, which the servlet
53 * can use to get any startup information, and the <code>getServletInfo</code>
54 * method, which allows the servlet to return basic information about itself,
55 * such as author, version, and copyright.
56 *
57 * @see GenericServlet
58 * @see javax.servlet.http.HttpServlet
59 *
60 * @version $Rev: 46019 $ $Date: 2004-09-14 02:56:06 -0700 (Tue, 14 Sep 2004) $
61 */
62 public interface Servlet {
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 configuration and initialization parameters
82 *
83 * @exception ServletException if an exception has occurred that
84 * interferes with the servlet's normal operation
85 *
86 * @see UnavailableException
87 * @see #getServletConfig
88 */
89 public void init(ServletConfig config) throws ServletException;
90
91 /**
92 * Returns a {@link ServletConfig} object, which contains
93 * initialization and startup parameters for this servlet.
94 * The <code>ServletConfig</code> object returned is the one
95 * passed to the <code>init</code> method.
96 *
97 * <p>Implementations of this interface are responsible for storing the
98 * <code>ServletConfig</code> object so that this
99 * method can return it. The {@link GenericServlet}
100 * class, which implements this interface, already does this.
101 *
102 * @return the <code>ServletConfig</code> object
103 * that initializes this servlet
104 *
105 * @see #init
106 */
107 public ServletConfig getServletConfig();
108
109 /**
110 * Called by the servlet container to allow the servlet to respond to
111 * a request.
112 *
113 * <p>This method is only called after the servlet's <code>init()</code>
114 * method has completed successfully.
115 *
116 * <p> The status code of the response always should be set for a servlet
117 * that throws or sends an error.
118 *
119 * <p>Servlets typically run inside multithreaded servlet containers
120 * that can handle multiple requests concurrently. Developers must
121 * be aware to synchronize access to any shared resources such as files,
122 * network connections, and as well as the servlet's class and instance
123 * variables.
124 * More information on multithreaded programming in Java is available in
125 * <a href="http://java.sun.com/Series/Tutorial/java/threads/multithreaded.html">
126 * the Java tutorial on multi-threaded programming</a>.
127 *
128 *
129 * @param req the <code>ServletRequest</code> object that contains
130 * the client's request
131 *
132 * @param res the <code>ServletResponse</code> object that contains
133 * the servlet's response
134 *
135 * @exception ServletException if an exception occurs that interferes
136 * with the servlet's normal operation
137 *
138 * @exception IOException if an input or output exception occurs
139 */
140 public void service(ServletRequest req, ServletResponse res)
141 throws ServletException, IOException;
142
143 /**
144 * Returns information about the servlet, such
145 * as author, version, and copyright.
146 *
147 * <p>The string that this method returns should
148 * be plain text and not markup of any kind (such as HTML, XML,
149 * etc.).
150 *
151 * @return a <code>String</code> containing servlet information
152 */
153 public String getServletInfo();
154
155 /**
156 * Called by the servlet container to indicate to a servlet that the
157 * servlet is being taken out of service. This method is
158 * only called once all threads within the servlet's
159 * <code>service</code> method have exited or after a timeout
160 * period has passed. After the servlet container calls this
161 * method, it will not call the <code>service</code> method again
162 * on this servlet.
163 *
164 * <p>This method gives the servlet an opportunity
165 * to clean up any resources that are being held (for example, memory,
166 * file handles, threads) and make sure that any persistent state is
167 * synchronized with the servlet's current state in memory.
168 */
169 public void destroy();
170 }