/*
 * $Id: HttpServlet.java,v 1.4 1999/04/20 20:37:45 sahmed Exp $
 * 
 * Copyright (c) 1996-1999 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information").  You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 * 
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 * 
 * CopyrightVersion 1.0
 *
 */

package javax.servlet.http;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Method;
import java.text.MessageFormat;
import java.util.Enumeration;
import java.util.ResourceBundle;

import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;


/**
 *
 * Provides an abstract class that you can subclass to create
 * an HTTP servlet, which receives requests from and
 * sends responses to a Web site. When you subclass 
 * <code>HttpServlet</code>, you must override at least 
 * one method, usually one of these:
 *
 * <ul>
 * <li> <code>doGet</code>, if the servlet supports HTTP GET requests
 * <li> <code>doPost</code>, for HTTP POST requests
 * <li> <code>doPut</code>, for HTTP PUT requests
 * <li> <code>doDelete</code>, for HTTP DELETE requests
 * <li> <code>init</code> and <code>destroy</code>, 
 * which you override as a pair if you need to 
 * manage resources that are held for the life of the servlet
 * <li> <code>getServletInfo</code>, which the servlet uses to
 * provide information about itself 
 * </ul>
 *
 * <p>You usually will not override the <code>service</code>
 * method. <code>service</code> handles standard HTTP
 * requests by dispatching them to the handler methods
 * for each HTTP request type (the <code>do</code><i>xxx</i>
 * methods listed above).
 *
 * <p>Likewise, you usually will not override the 
 * <code>doOptions</code> and <code>doTrace</code> methods.
 * The <code>service</code> method supports HTTP 1.1
 * TRACE and OPTIONS requests by dispatching them to
 * <code>doTrace</code> and <code>doOptions</code>.
 * 
 * <p>Servlets typically run on multithreaded servers,
 * so you must write your servlet to handle concurrent
 * requests and synchronize access to shared resources.
 * Shared resources include in-memory data such as
 * instance or class variables and external objects
 * such as files, database connections, and network 
 * connections.
 * See the
 * <a href="http://java.sun.com/Series/Tutorial/java/threads/multithreaded.html">
 * Java Tutorial on Multithreaded Programming</a> for more
 * information on handling multiple threads in a Java program.
 *
 * @author	Various
 * @version	$Version$
 *
 */



public abstract class HttpServlet extends GenericServlet
    implements java.io.Serializable
{
    private static final String METHOD_DELETE = "DELETE";
    private static final String METHOD_HEAD = "HEAD";
    private static final String METHOD_GET = "GET";
    private static final String METHOD_OPTIONS = "OPTIONS";
    private static final String METHOD_POST = "POST";
    private static final String METHOD_PUT = "PUT";
    private static final String METHOD_TRACE = "TRACE";

    private static final String HEADER_IFMODSINCE = "If-Modified-Since";
    private static final String HEADER_LASTMOD = "Last-Modified";
    
    private static final String LSTRING_FILE =
	"javax.servlet.http.LocalStrings";
    private static ResourceBundle lStrings =
	ResourceBundle.getBundle(LSTRING_FILE);
   
   
   
    
    /**
     * Does nothing, because this is an abstract class.
     * 
     */

    public HttpServlet () { }
    
    

    /**
     *
     * Receives an HTTP GET request from the protected
     * <code>service</code> method and handles the request. 
     * The GET method allows a client to read information
     * from the Web server, passing a query string appended
     * to an URL to tell the server what information
     * to return.
     *
     * <p>Overriding this method to support a GET request also
     * automatically supports an HTTP HEAD request. A HEAD

     * request is a GET request that returns no body in the
     * response, only the request header fields.
     *
     * <p>If you override this method, you should read data from
     * the request, set entity headers in the response, 
     * access the writer or output stream object, and finally,
     * write the response data. When you set headers, be
     * sure to include content type and encoding. If you use
     * a <code>PrintWriter</code> object to return the response,
     * you must set the content type before you access the
     * <code>PrintWriter</code> object.
     *
     * <p>The servlet engine must write the headers before
     * the response data, because the headers can be flushed
     * at any time after the data is written.
     *
     * <p>If you can set the Content-Length header (with the
     * {@link javax.servlet.ServletResponse.#contentType} method),
     * the servlet
     * can use a persistent connection to return its response
     * to the client, improving performance dramatically.
     * If you cannot set Content-Length, you can sometimes avoid
     * the performance penalty if the response fits in an internal
     * buffer.
     * 
     * <p>The GET method should be safe, that is, without
     * any side effects for which users are held responsible.
     * For example, most form queries have no side effects.
     * If a client request is intended to change stored data,
     * the request should use some other HTTP method.
     *
     * <p>The GET method should also be idempotent, meaning
     * that it can be safely repeated. Sometimes making a
     * method safe also makes it idempotent. For example, 
     * repeating queries is both safe and idempotent, but
     * buying a product online or modifying data is neither
     * safe nor idempotent. 
     *
     * <p>If the request is incorrectly formatted, <code>doGet</code>
     * returns an HTTP BAD_REQUEST message.
     * 
     *
     * @param req	an {@link HttpServletRequest} object that
     *			contains the request the client has made
     *			of the servlet
     *
     * @param resp	an {@link HttpServletResponse} object that
     *			contains the response the servlet sends
     *			to the object
     * 
     * @exception IOException	if an input or output error is 
     *				detected when the servlet handles
     *				the GET request
     *
     * @exception ServletException	if the request for the GET
     *					could not be handled
     *
     * 
     * @see javax.servlet.ServletResponse#setContentType
     *
     */

    protected void doGet (HttpServletRequest req, HttpServletResponse resp)
	throws ServletException, IOException
    {
	String protocol = req.getProtocol();
	String msg = lStrings.getString("http.method_get_not_supported");
	if (protocol.endsWith("1.1")) {
	    resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
	} else {
	    resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
	}
    }





    /**
     *
     * Returns the time the <code>HttpServletRequest</code>
     * object was last modified,
     * in milliseconds since midnight January 1, 1970 GMT.
     * If the time is unknown, this method returns a negative
     * number.
     *
     * <p>Servlet engines that support HTTP GET requests
     * should override <code>getLastModified</code> to
     * provide an accurate object modification time. This
     * makes browser and proxy caches work more effectively,
     * reducing the load on server and network resources.
     *
     *
     * @param req	the <code>HttpServletRequest</code> 
     *			object that is sent to the servlet
     *
     * @return		a <code>long</code> integer specifying
     *			the time the <code>HttpServletRequest</code>
     *			object was last modified, in milliseconds
     *			since midnight, January 1, 1970 GMT, or
     *			-1 if the time is not known
     *
     */

    protected long getLastModified (HttpServletRequest req) {
	return -1;
    }




    /*
     * Private method; not a Javadoc comment
     *
     * <p>Receives an HTTP HEAD request from the protected
     * <code>service</code> method and handles the
     * request.
     * The client sends a HEAD request when it wants
     * to see only the headers of a response, such as
     * Content-Type or Content-Length. The HTTP HEAD

     * method counts the output bytes in the response
     * to set the Content-Length header accurately.
     *
     * <p>If you override this method, you can avoid computing
     * the response body and just set the response headers
     * directly to improve performance. Make sure that the
     * <code>doHead</code> method you write is both safe
     * and idempotent (that is, protects itself from being
     * called multiple times for one HTTP HEAD request).
     *
     * <p>If the HTTP HEAD request is incorrectly formatted,
     * <code>doHead</code> returns an HTTP BAD_REQUEST
     * message.
     *
     *
     * @param req	the request object that is passed
     *			to the servlet
     *			
     * @param resp	the response object that the servlet
     *			uses to return the headers to the clien
     *
     * @exception IOException		if an input or output error occurs
     *
     * @exception ServletException	if the request for the HEAD
     *					could not be handled
     */

    private void doHead (HttpServletRequest req, HttpServletResponse resp)
	throws ServletException, IOException
    {
	NoBodyResponse response = new NoBodyResponse(resp);
	
	doGet (req, response);
	response.setContentLength ();
    }
    




    /**
     *
     * Receives an HTTP POST request from the protected
     * <code>service</code> method and handles the request.
     * The HTTP POST method allows the client to send
     * data of unlimited length to the Web server once
     * and is useful when posting information such as
     * credit card numbers.
     *
     * <p>If you override this method, you should read data from
     * the <code>HttpServletRequest</code> object, set headers
     * for the response (including Content-Type and Content-Encoding), 
     * access a <code>PrintWriter</code> or
     * output stream object, and then write any response data
     * using a {@link javax.servlet.ServletOutputStream} object.
     *
     * <p>If you use a <code>PrintWriter</code> object to
     * write response data, set the Content-Type header before 
     * you access the <code>PrintWriter</code> object.
     * The servlet engine must write the headers before the
     * the response data, because the headers can be flushed at
     * any time after the servlet engine begins to write the body 
     * of the response.
     *
     * <p>If you use HTTP 1.1 chunked encoding (which means that
     * the response has a Transfer-Encoding header), do not set the
     * Content-Length header. If you do not use
     * chunked encoding, set the content length to allow the servlet
     * to take advantage of the HTTP "connection keep alive" feature,
     * If you cannot set the content length and therefore cannot
     * use "keep alive," you may be able to avoid the performance 
     * penalty if the response fits in an internal buffer.
     *
     * <p>This method does not need to be either safe or idempotent.
     * Operations requested through POST can have side effects for
     * which the user can be held accountable, for example, 
     * updating stored data or buying items online.
     *
     * <p>If the HTTP POST request is incorrectly formatted,
     * <code>doPost</code> returns an HTTP BAD_REQUEST message.
     *
     *
     * @param req	an {@link HttpServletRequest} object that
     *			contains the request the client has made
     *			of the servlet
     *