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Tomcat example source code file (Servlet.java)

This example Tomcat source code file (Servlet.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Tomcat tags/keywords

io, ioexception, ioexception, servlet, servlet, servletconfig, servletexception, servletexception, servletresponse, string, string

The Tomcat Servlet.java source code

/*
* 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 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 or an HTTP servlet that
 * extends <code>javax.servlet.http.HttpServlet.
 *
 * <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 init method.
 * <li>Any calls from clients to the service method are handled.
 * <li>The servlet is taken out of service, then destroyed with the 
 * <code>destroy method, then garbage collected and finalized.
 * </ol>
 *
 * <p>In addition to the life-cycle methods, this interface
 * provides the <code>getServletConfig method, which the servlet 
 * can use to get any startup information, and the <code>getServletInfo
 * method, which allows the servlet to return basic information about itself,
 * such as author, version, and copyright.
 *
 * @author 	Various
 * @version 	$Version$
 *
 * @see 	GenericServlet
 * @see 	javax.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 init
     * method exactly once after instantiating the servlet.
     * The <code>init 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 method
     * <ol>
     * <li>Throws a ServletException
     * <li>Does not return within a time period defined by the Web server
     * </ol>
     *
     *
     * @param config			a <code>ServletConfig 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 object returned is the one 
     * passed to the <code>init method. 
     *
     * <p>Implementations of this interface are responsible for storing the 
     * <code>ServletConfig object so that this 
     * method can return it. The {@link GenericServlet}
     * class, which implements this interface, already does this.
     *
     * @return		the <code>ServletConfig 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 init()
     * 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 object that contains
     *			the client's request
     *
     * @param res 	the <code>ServletResponse 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 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 method have exited or after a timeout
     * period has passed. After the servlet container calls this 
     * method, it will not call the <code>service 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();
}

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