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   * Copyright (c) 1997-2010 Oracle and/or its affiliates. All rights reserved.
   * The contents of this file are subject to the terms of either the GNU
   * General Public License Version 2 only ("GPL") or the Common Development
   * and Distribution License("CDDL") (collectively, the "License").  You
   * may not use this file except in compliance with the License.  You can
  * obtain a copy of the License at
  * or packager/legal/LICENSE.txt.  See the License for the specific
  * language governing permissions and limitations under the License.
  * When distributing the software, include this License Header Notice in each
  * file and include the License file at packager/legal/LICENSE.txt.
  * GPL Classpath Exception:
  * Oracle designates this particular file as subject to the "Classpath"
  * exception as provided by Oracle in the GPL Version 2 section of the License
  * file that accompanied this code.
  * Modifications:
  * If applicable, add the following below the License Header, with the fields
  * enclosed by brackets [] replaced by your own identifying information:
  * "Portions Copyright [year] [name of copyright owner]"
  * Contributor(s):
  * If you wish your version of this file to be governed by only the CDDL or
  * only the GPL Version 2, indicate your decision by adding "[Contributor]
  * elects to include this software in this distribution under the [CDDL or GPL
  * Version 2] license."  If you don't indicate a single choice of license, a
  * recipient has the option to distribute your version of this file under
  * either the CDDL, the GPL Version 2 or to extend the choice of license to
  * its licensees as provided above.  However, if you add GPL Version 2 code
  * and therefore, elected the GPL Version 2 license, then the option applies
  * only if the new code is made subject to such option by the copyright
  * holder.
  * This file incorporates work covered by the following copyright and
  * permission notice:
  * Copyright 2004 The Apache Software Foundation
  * Licensed 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
  * 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 javax.servlet;
Defines methods that all servlets must implement.

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.

To implement this interface, you can write a generic servlet that extends javax.servlet.GenericServlet or an HTTP servlet that extends javax.servlet.http.HttpServlet.

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:

  1. The servlet is constructed, then initialized with the init method.
  2. Any calls from clients to the service method are handled.
  3. The servlet is taken out of service, then destroyed with the destroy method, then garbage collected and finalized.

In addition to the life-cycle methods, this interface provides the getServletConfig method, which the servlet can use to get any startup information, and the getServletInfo method, which allows the servlet to return basic information about itself, such as author, version, and copyright.

public interface Servlet {

Called by the servlet container to indicate to a servlet that the servlet is being placed into service.

The servlet container calls the init method exactly once after instantiating the servlet. The init method must complete successfully before the servlet can receive any requests.

The servlet container cannot place the servlet into service if the init method

  1. Throws a ServletException
  2. Does not return within a time period defined by the Web server

config a ServletConfig object containing the servlet's configuration and initialization parameters
ServletException if an exception has occurred that interferes with the servlet's normal operation
See also:
    public void init(ServletConfig configthrows ServletException;

Returns a ServletConfig object, which contains initialization and startup parameters for this servlet. The ServletConfig object returned is the one passed to the init method.

Implementations of this interface are responsible for storing the ServletConfig object so that this method can return it. The GenericServlet class, which implements this interface, already does this.

the ServletConfig object that initializes this servlet
See also:
    public ServletConfig getServletConfig();

Called by the servlet container to allow the servlet to respond to a request.

This method is only called after the servlet's init() method has completed successfully.

The status code of the response always should be set for a servlet that throws or sends an error.

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 the Java tutorial on multi-threaded programming.

req the ServletRequest object that contains the client's request
res the ServletResponse object that contains the servlet's response
ServletException if an exception occurs that interferes with the servlet's normal operation if an input or output exception occurs
    public void service(ServletRequest reqServletResponse res)
	throws ServletExceptionIOException;

Returns information about the servlet, such as author, version, and copyright.

The string that this method returns should be plain text and not markup of any kind (such as HTML, XML, etc.).

a String 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 service method have exited or after a timeout period has passed. After the servlet container calls this method, it will not call the service method again on this servlet.

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();
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