geronimo-servlet_3.0_spec/src/main/java/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/>
 * <p>This interface is intended to wrap servlets,
 * but a servlet container can create <code>RequestDispatcher</code>
 * objects to wrap any type of resource.
 *
 * @version $Rev$ $Date$
 * 
 * @see ServletContext#getRequestDispatcher(java.lang.String)
 * @see ServletContext#getNamedDispatcher(java.lang.String)
 * @see ServletRequest#getRequestDispatcher(java.lang.String)
 */

public interface RequestDispatcher {

    //constants since 3.0
    
    String ERROR_EXCEPTION = "javax.servlet.error.exception";
    String ERROR_EXCEPTION_TYPE = "javax.servlet.error.exception_type";
    String ERROR_MESSAGE = "javax.servlet.error.message";
    String ERROR_REQUEST_URI = "javax.servlet.error.request_uri";
    String ERROR_SERVLET_NAME = "javax.servlet.error.servlet_name";
    String ERROR_STATUS_CODE = "javax.servlet.error.status_code";
    String FORWARD_CONTEXT_PATH = "javax.servlet.forward.context_path";
    String FORWARD_PATH_INFO = "javax.servlet.forward.path_info";
    String FORWARD_QUERY_STRING = "javax.servlet.forward.query_string";
    String FORWARD_REQUEST_URI = "javax.servlet.forward.request_uri";
    String FORWARD_SERVLET_PATH = "javax.servlet.forward.servlet_path";
    String INCLUDE_CONTEXT_PATH = "javax.servlet.include.context_path";
    String INCLUDE_PATH_INFO = "javax.servlet.include.path_info";
    String INCLUDE_QUERY_STRING = "javax.servlet.include.query_string";
    String INCLUDE_REQUEST_URI = "javax.servlet.include.request_uri";
    String INCLUDE_SERVLET_PATH = "javax.servlet.include.servlet_path";

    /**
     * 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/>
     * <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/>
     * <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/>
     * <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
     * @throws ServletException      if the target resource throws this exception
     * @throws IOException           if the target resource throws this exception
     * @throws 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/>
     * <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/>
     * <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
     * @throws ServletException if the included resource throws this exception
     * @throws IOException      if the included resource throws this exception
     */
    public void include(ServletRequest request, ServletResponse response) throws ServletException, IOException;

}