httpservlet.java

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/*
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 1999 The Apache Software Foundation.  All rights 
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowlegement:  
 *       "This product includes software developed by the 
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 *
 * 4. The names "The Jakarta Project", "Tomcat", and "Apache Software
 *    Foundation" must not be used to endorse or promote products derived
 *    from this software without prior written permission. For written 
 *    permission, please contact [e-mail].
 *
 * 5. Products derived from this software may not be called "Apache"
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 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 * ====================================================================
 *
 * 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.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.Locale;
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 to be subclassed to create
 * an HTTP servlet suitable for a Web site. A subclass of
 * <code>HttpServlet</code> 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>, 
 * 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>There's almost no reason to 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, there's almost no reason to override the 
 * <code>doOptions</code> and <code>doTrace</code> methods.
 * 
 * <p>Servlets typically run on multithreaded servers,
 * so be aware that a servlet must handle concurrent
 * requests and be careful to 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() { }
    
    

    /**
     *
     * Called by the server (via the <code>service</code> method) to
     * allow a servlet to handle a GET request. 
     *
     * <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>When overriding this method, read the request data,
     * write the response headers, get the response's writer or 
     * output stream object, and finally, write the response data.
     * It's best to include content type and encoding. When using
     * a <code>PrintWriter</code> object to return the response,
     * set the content type before accessing the
     * <code>PrintWriter</code> object.
     *
     * <p>The servlet container must write the headers before
     * committing the response, because in HTTP the headers must be sent
     * before the response body.
     *
     * <p>Where possible, set the Content-Length header (with the
     * {@link javax.servlet.ServletResponse#setContentLength} method),
     * to allow the servlet container to use a persistent connection 
     * to return its response to the client, improving performance.
     * The content length is automatically set if the entire response fits
     * inside the response 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 client
     * 
     * @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 (the default).
     *
     * <p>Servlets that support HTTP GET requests and can quickly determine
     * their last modification time should override this method.
     * 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();
    }
    




    /**
     *
     * Called by the server (via the <code>service</code> method)
     * to allow a servlet to handle a POST request.
     *
     * The HTTP POST method allows the client to send
     * data of unlimited length to the Web server a single time
     * and is useful when posting information such as
     * credit card numbers.
     *
     * <p>When overriding this method, read the request data,
     * write the response headers, get the response's writer or output
     * stream object, and finally, write the response data. It's best 
     * to include content type and encoding. When using a
     * <code>PrintWriter</code> object to return the response, set the 
     * content type before accessing the <code>PrintWriter</code> object. 
     *
     * <p>The servlet container must write the headers before committing the
     * response, because in HTTP the headers must be sent before the 
     * response body.
     *
     * <p>Where possible, set the Content-Length header (with the
     * {@link javax.servlet.ServletResponse#setContentLength} method),
     * to allow the servlet container to use a persistent connection 
     * to return its response to the client, improving performance.
     * The content length is automatically set if the entire response fits
     * inside the response buffer.  
     *
     * <p>When using HTTP 1.1 chunked encoding (which means that the response
     * has a Transfer-Encoding header), do not set the Content-Length header. 
     *
     * <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,