/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package jakarta.servlet;
import java.io.IOException;
/**
* Defines methods that all servlets must implement.
* <p>
* A servlet is a small Java program that runs within a Web server. Servlets receive and respond to requests from Web
* clients, usually across HTTP, the HyperText Transfer Protocol.
* <p>
* To implement this interface, you can write a generic servlet that extends <code>jakarta.servlet.GenericServlet</code>
* or an HTTP servlet that extends <code>jakarta.servlet.http.HttpServlet</code>.
* <p>
* This interface defines methods to initialize a servlet, to service requests, and to remove a servlet from the server.
* These are known as life-cycle methods and are called in the following sequence:
* <ol>
* <li>The servlet is constructed, then initialized with the <code>init</code> method.
* <li>Any calls from clients to the <code>service</code> method are handled.
* <li>The servlet is taken out of service, then destroyed with the <code>destroy</code> method, then garbage collected
* and finalized.
* </ol>
* <p>
* In addition to the life-cycle methods, this interface provides the <code>getServletConfig</code> method, which the
* servlet can use to get any startup information, and the <code>getServletInfo</code> method, which allows the servlet
* to return basic information about itself, such as author, version, and copyright.
*
* @see GenericServlet
* @see jakarta.servlet.http.HttpServlet
*/
public interface Servlet {
/**
* Called by the servlet container to indicate to a servlet that the servlet is being placed into service.
* <p>
* The servlet container calls the <code>init</code> method exactly once after instantiating the servlet. The
* <code>init</code> method must complete successfully before the servlet can receive any requests.
* <p>
* The servlet container cannot place the servlet into service if the <code>init</code> method
* <ol>
* <li>Throws a <code>ServletException</code>
* <li>Does not return within a time period defined by the Web server
* </ol>
*
* @param config a <code>ServletConfig</code> object containing the servlet's configuration and initialization
* parameters
*
* @exception ServletException if an exception has occurred that interferes with the servlet's normal operation
*
* @see UnavailableException
* @see #getServletConfig
*/
void init(ServletConfig config) throws ServletException;
/**
* Returns a {@link ServletConfig} object, which contains initialization and startup parameters for this servlet.
* The <code>ServletConfig</code> object returned is the one passed to the <code>init</code> method.
* <p>
* Implementations of this interface are responsible for storing the <code>ServletConfig</code> object so that this
* method can return it. The {@link GenericServlet} class, which implements this interface, already does this.
*
* @return the <code>ServletConfig</code> object that initializes this servlet
*
* @see #init
*/
ServletConfig getServletConfig();
/**
* Called by the servlet container to allow the servlet to respond to a request.
* <p>
* This method is only called after the servlet's <code>init()</code> method has completed successfully.
* <p>
* The status code of the response always should be set for a servlet that throws or sends an error.
* <p>
* Servlets typically run inside multithreaded servlet containers that can handle multiple requests concurrently.
* Developers must be aware to synchronize access to any shared resources such as files, network connections, and as
* well as the servlet's class and instance variables. More information on multithreaded programming in Java is
* available in <a href="http://java.sun.com/Series/Tutorial/java/threads/multithreaded.html"> the Java tutorial on
* multi-threaded programming</a>.
*
* @param req the <code>ServletRequest</code> object that contains the client's request
* @param res the <code>ServletResponse</code> object that contains the servlet's response
*
* @exception ServletException if an exception occurs that interferes with the servlet's normal operation
* @exception IOException if an input or output exception occurs
*/
void service(ServletRequest req, ServletResponse res) throws ServletException, IOException;
/**
* Returns information about the servlet, such as author, version, and copyright.
* <p>
* The string that this method returns should be plain text and not markup of any kind (such as HTML, XML, etc.).
*
* @return a <code>String</code> containing servlet information
*/
String getServletInfo();
/**
* Called by the servlet container to indicate to a servlet that the servlet is being taken out of service. This
* method is only called once all threads within the servlet's <code>service</code> method have exited or after a
* timeout period has passed. After the servlet container calls this method, it will not call the
* <code>service</code> method again on this servlet.
* <p>
* This method gives the servlet an opportunity to clean up any resources that are being held (for example, memory,
* file handles, threads) and make sure that any persistent state is synchronized with the servlet's current state
* in memory.
*/
void destroy();
}
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