/*
 * 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.
 */

//
// This source code implements specifications defined by the Java
// Community Process. In order to remain compliant with the specification
// DO NOT add / change / or delete method signatures!
//

package javax.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>javax.servlet.GenericServlet</code> or an HTTP servlet that
 * extends <code>javax.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 javax.servlet.http.HttpServlet
 *
 * @version $Rev: 467553 $ $Date: 2006-10-25 06:01:51 +0200 (Wed, 25 Oct 2006) $
 */
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
     */
    public 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
     */
    public 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
     */
    public 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
     */
    public 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.
     */
    public void destroy();
}
