servletapi/jsr154/src/share/javax/servlet/RequestDispatcher.java

/*
* 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 an object that receives requests from the client
 * and sends them to any resource (such as a servlet, 
 * HTML file, or JSP file) on the server. The servlet
 * container creates the <code>RequestDispatcher</code> object,
 * which is used as a wrapper around a server resource located
 * at a particular path or given by a particular name.
 *
 * <p>This interface is intended to wrap servlets,
 * but a servlet container can create <code>RequestDispatcher</code>
 * objects to wrap any type of resource.
 *
 * @author 	Various
 * @version 	$Version$
 *
 * @see 	ServletContext#getRequestDispatcher(java.lang.String)
 * @see 	ServletContext#getNamedDispatcher(java.lang.String)
 * @see 	ServletRequest#getRequestDispatcher(java.lang.String)
 *
 */
 
public interface RequestDispatcher {





/**
 * Forwards a request from
 * a servlet to another resource (servlet, JSP file, or
 * HTML file) on the server. This method allows
 * one servlet to do preliminary processing of
 * a request and another resource to generate
 * the response.
 *
 * <p>For a <code>RequestDispatcher</code> obtained via 
 * <code>getRequestDispatcher()</code>, the <code>ServletRequest</code> 
 * object has its path elements and parameters adjusted to match
 * the path of the target resource.
 *
 * <p><code>forward</code> should be called before the response has been 
 * committed to the client (before response body output has been flushed).  
 * If the response already has been committed, this method throws
 * an <code>IllegalStateException</code>.
 * Uncommitted output in the response buffer is automatically cleared 
 * before the forward.
 *
 * <p>The request and response parameters must be either the same
 * objects as were passed to the calling servlet's service method or be
 * subclasses of the {@link ServletRequestWrapper} or {@link ServletResponseWrapper} classes
 * that wrap them.
 *
 *
 * @param request		a {@link ServletRequest} object
 *				that represents the request the client
 * 				makes of the servlet
 *
 * @param response		a {@link ServletResponse} object
 *				that represents the response the servlet
 *				returns to the client
 *
 * @exception ServletException	if the target resource throws this exception
 *
 * @exception IOException	if the target resource throws this exception
 *
 * @exception IllegalStateException	if the response was already committed
 *
 */

    public void forward(ServletRequest request, ServletResponse response)
	throws ServletException, IOException;




    /**
     *
     * Includes the content of a resource (servlet, JSP page,
     * HTML file) in the response. In essence, this method enables 
     * programmatic server-side includes.
     *
     * <p>The {@link ServletResponse} object has its path elements
     * and parameters remain unchanged from the caller's. The included
     * servlet cannot change the response status code or set headers;
     * any attempt to make a change is ignored.
     *
     * <p>The request and response parameters must be either the same
     * objects as were passed to the calling servlet's service method or be
     * subclasses of the {@link ServletRequestWrapper} or {@link ServletResponseWrapper} classes
     * that wrap them.
     * 
     *
     *
     * @param request 			a {@link ServletRequest} object 
     *					that contains the client's request
     *
     * @param response 			a {@link ServletResponse} object 
     * 					that contains the servlet's response
     *
     * @exception ServletException 	if the included resource throws this exception
     *
     * @exception IOException 		if the included resource throws this exception
     *
     *
     */
     
    public void include(ServletRequest request, ServletResponse response)
	throws ServletException, IOException;
}