/*
 * Copyright (c) 1997, 2021 Oracle and/or its affiliates and others.
 * All rights reserved.
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed 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 jakarta.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
 *
 * @see ServletContext#getRequestDispatcher(java.lang.String)
 * @see ServletContext#getNamedDispatcher(java.lang.String)
 * @see ServletRequest#getRequestDispatcher(java.lang.String)
 */
public interface RequestDispatcher {

    /**
     * The name of the request attribute under which the original request URI is made available to the target of a
     * {@link #forward(ServletRequest,ServletResponse) forward}
     *
     * @since Servlet 3.0
     */
    static final String FORWARD_REQUEST_URI = "jakarta.servlet.forward.request_uri";

    /**
     * The name of the request attribute under which the original context path is made available to the target of a
     * {@link #forward(ServletRequest,ServletResponse) forward}
     *
     * @since Servlet 3.0
     */
    static final String FORWARD_CONTEXT_PATH = "jakarta.servlet.forward.context_path";

    /**
     * The name of the request attribute under which the original {@link jakarta.servlet.http.HttpServletMapping} is made
     * available to the target of a {@link #forward(ServletRequest,ServletResponse) forward}
     * 
     * @since Servlet 4.0
     */
    static final String FORWARD_MAPPING = "jakarta.servlet.forward.mapping";

    /**
     * The name of the request attribute under which the original path info is made available to the target of a
     * {@link #forward(ServletRequest,ServletResponse) forward}
     *
     * @since Servlet 3.0
     */
    static final String FORWARD_PATH_INFO = "jakarta.servlet.forward.path_info";

    /**
     * The name of the request attribute under which the original servlet path is made available to the target of a
     * {@link #forward(ServletRequest,ServletResponse) forward}
     *
     * @since Servlet 3.0
     */
    static final String FORWARD_SERVLET_PATH = "jakarta.servlet.forward.servlet_path";

    /**
     * The name of the request attribute under which the original query string is made available to the target of a
     * {@link #forward(ServletRequest,ServletResponse) forward}
     *
     * @since Servlet 3.0
     */
    static final String FORWARD_QUERY_STRING = "jakarta.servlet.forward.query_string";

    /**
     * The name of the request attribute under which the request URI of the target of an
     * {@link #include(ServletRequest,ServletResponse) include} is stored
     *
     * @since Servlet 3.0
     */
    static final String INCLUDE_REQUEST_URI = "jakarta.servlet.include.request_uri";

    /**
     * The name of the request attribute under which the context path of the target of an
     * {@link #include(ServletRequest,ServletResponse) include} is stored
     *
     * @since Servlet 3.0
     */
    static final String INCLUDE_CONTEXT_PATH = "jakarta.servlet.include.context_path";

    /**
     * The name of the request attribute under which the path info of the target of an
     * {@link #include(ServletRequest,ServletResponse) include} is stored
     *
     * @since Servlet 3.0
     */
    static final String INCLUDE_PATH_INFO = "jakarta.servlet.include.path_info";

    /**
     * The name of the request attribute under which the {@link jakarta.servlet.http.HttpServletMapping} of the target of an
     * {@link #include(ServletRequest,ServletResponse) include} is stored
     *
     * @since Servlet 4.0
     */
    static final String INCLUDE_MAPPING = "jakarta.servlet.include.mapping";

    /**
     * The name of the request attribute under which the servlet path of the target of an
     * {@link #include(ServletRequest,ServletResponse) include} is stored
     *
     * @since Servlet 3.0
     */
    static final String INCLUDE_SERVLET_PATH = "jakarta.servlet.include.servlet_path";

    /**
     * The name of the request attribute under which the query string of the target of an
     * {@link #include(ServletRequest,ServletResponse) include} is stored
     *
     * @since Servlet 3.0
     */
    static final String INCLUDE_QUERY_STRING = "jakarta.servlet.include.query_string";

    /**
     * The name of the request attribute under which the exception object is propagated during an error dispatch
     *
     * @since Servlet 3.0
     */
    public static final String ERROR_EXCEPTION = "jakarta.servlet.error.exception";

    /**
     * The name of the request attribute under which the type of the exception object is propagated during an error dispatch
     *
     * @since Servlet 3.0
     */
    public static final String ERROR_EXCEPTION_TYPE = "jakarta.servlet.error.exception_type";

    /**
     * The name of the request attribute under which the exception message is propagated during an error dispatch
     *
     * @since Servlet 3.0
     */
    public static final String ERROR_MESSAGE = "jakarta.servlet.error.message";

    /**
     * The name of the request attribute under which the request URI whose processing caused the error is propagated during
     * an error dispatch
     *
     * @since Servlet 3.0
     */
    public static final String ERROR_REQUEST_URI = "jakarta.servlet.error.request_uri";

    /**
     * The name of the request attribute under which the name of the servlet in which the error occurred is propagated
     * during an error dispatch
     *
     * @since Servlet 3.0
     */
    public static final String ERROR_SERVLET_NAME = "jakarta.servlet.error.servlet_name";

    /**
     * The name of the request attribute under which the response status is propagated during an error dispatch
     *
     * @since Servlet 3.0
     */
    public static final String ERROR_STATUS_CODE = "jakarta.servlet.error.status_code";

    /**
     * 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.
     *
     * <p>
     * This method sets the dispatcher type of the given request to <code>DispatcherType.FORWARD</code>.
     *
     * @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
     *
     * @see ServletRequest#getDispatcherType
     */
    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.
     *
     * <p>
     * This method sets the dispatcher type of the given request to <code>DispatcherType.INCLUDE</code>.
     *
     * @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
     *
     * @see ServletRequest#getDispatcherType
     */
    public void include(ServletRequest request, ServletResponse response) throws ServletException, IOException;
}