/*
 * 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.
 *
 * @see ServletContext#getRequestDispatcher(String)
 * @see ServletContext#getNamedDispatcher(String)
 * @see ServletRequest#getRequestDispatcher(String)
 */
public interface RequestDispatcher {

    /**
     * The name of the request attribute that should be set by the container when the
     * {@link #forward(ServletRequest, ServletResponse)} method is called. It provides the original value of a
     * path-related property of the request. See the chapter "Forwarded Request Parameters" in the Servlet Specification
     * for details.
     *
     * @since Servlet 3.0
     */
    String FORWARD_REQUEST_URI = "javax.servlet.forward.request_uri";

    /**
     * The name of the request attribute that should be set by the container when the
     * {@link #forward(ServletRequest, ServletResponse)} method is called. It provides the original value of a
     * path-related property of the request. See the chapter "Forwarded Request Parameters" in the Servlet Specification
     * for details.
     *
     * @since Servlet 3.0
     */
    String FORWARD_CONTEXT_PATH = "javax.servlet.forward.context_path";

    /**
     * The name of the request attribute that should be set by the container when the
     * {@link #forward(ServletRequest, ServletResponse)} method is called. It provides the original value of a
     * path-related property of the request. See the chapter "Forwarded Request Parameters" in the Servlet Specification
     * for details.
     *
     * @since Servlet 3.0
     */
    String FORWARD_PATH_INFO = "javax.servlet.forward.path_info";

    /**
     * The name of the request attribute that should be set by the container when the
     * {@link #forward(ServletRequest, ServletResponse)} method is called. It provides the original value of a
     * path-related property of the request. See the chapter "Forwarded Request Parameters" in the Servlet Specification
     * for details.
     *
     * @since Servlet 3.0
     */
    String FORWARD_SERVLET_PATH = "javax.servlet.forward.servlet_path";

    /**
     * The name of the request attribute that should be set by the container when the
     * {@link #forward(ServletRequest, ServletResponse)} method is called. It provides the original value of a
     * path-related property of the request. See the chapter "Forwarded Request Parameters" in the Servlet Specification
     * for details.
     *
     * @since Servlet 3.0
     */
    String FORWARD_QUERY_STRING = "javax.servlet.forward.query_string";

    /**
     * The name of the request attribute that should be set by the container when the
     * {@link #include(ServletRequest, ServletResponse)} method is called on the {@code RequestDispatcher} obtained by a
     * path and not by a name. It provides information on the path that was used to obtain the {@code RequestDispatcher}
     * instance for this include call. See the chapter "Included Request Parameters" in the Servlet Specification for
     * details.
     *
     * @since Servlet 3.0
     */
    String INCLUDE_REQUEST_URI = "javax.servlet.include.request_uri";

    /**
     * The name of the request attribute that should be set by the container when the
     * {@link #include(ServletRequest, ServletResponse)} method is called on the {@code RequestDispatcher} obtained by a
     * path and not by a name. It provides information on the path that was used to obtain the {@code RequestDispatcher}
     * instance for this include call. See the chapter "Included Request Parameters" in the Servlet Specification for
     * details.
     *
     * @since Servlet 3.0
     */
    String INCLUDE_CONTEXT_PATH = "javax.servlet.include.context_path";

    /**
     * The name of the request attribute that should be set by the container when the
     * {@link #include(ServletRequest, ServletResponse)} method is called on the {@code RequestDispatcher} obtained by a
     * path and not by a name. It provides information on the path that was used to obtain the {@code RequestDispatcher}
     * instance for this include call. See the chapter "Included Request Parameters" in the Servlet Specification for
     * details.
     *
     * @since Servlet 3.0
     */
    String INCLUDE_PATH_INFO = "javax.servlet.include.path_info";

    /**
     * The name of the request attribute that should be set by the container when the
     * {@link #include(ServletRequest, ServletResponse)} method is called on the {@code RequestDispatcher} obtained by a
     * path and not by a name. It provides information on the path that was used to obtain the {@code RequestDispatcher}
     * instance for this include call. See the chapter "Included Request Parameters" in the Servlet Specification for
     * details.
     *
     * @since Servlet 3.0
     */
    String INCLUDE_SERVLET_PATH = "javax.servlet.include.servlet_path";

    /**
     * The name of the request attribute that should be set by the container when the
     * {@link #include(ServletRequest, ServletResponse)} method is called on the {@code RequestDispatcher} obtained by a
     * path and not by a name. It provides information on the path that was used to obtain the {@code RequestDispatcher}
     * instance for this include call. See the chapter "Included Request Parameters" in the Servlet Specification for
     * details.
     *
     * @since Servlet 3.0
     */
    String INCLUDE_QUERY_STRING = "javax.servlet.include.query_string";

    /**
     * The name of the request attribute that should be set by the container when custom error-handling servlet or JSP
     * page is invoked. The value of the attribute is of type {@code java.lang.Throwable}. See the chapter "Error
     * Handling" in the Servlet Specification for details.
     *
     * @since Servlet 3.0
     */
    String ERROR_EXCEPTION = "javax.servlet.error.exception";

    /**
     * The name of the request attribute that should be set by the container when custom error-handling servlet or JSP
     * page is invoked. The value of the attribute is of type {@code java.lang.Class}. See the chapter "Error Handling"
     * in the Servlet Specification for details.
     *
     * @since Servlet 3.0
     */
    String ERROR_EXCEPTION_TYPE = "javax.servlet.error.exception_type";

    /**
     * The name of the request attribute that should be set by the container when custom error-handling servlet or JSP
     * page is invoked. The value of the attribute is of type {@code String}. See the chapter "Error Handling" in the
     * Servlet Specification for details.
     *
     * @since Servlet 3.0
     */
    String ERROR_MESSAGE = "javax.servlet.error.message";

    /**
     * The name of the request attribute that should be set by the container when custom error-handling servlet or JSP
     * page is invoked. The value of the attribute is of type {@code String}. See the chapter "Error Handling" in the
     * Servlet Specification for details.
     *
     * @since Servlet 3.0
     */
    String ERROR_REQUEST_URI = "javax.servlet.error.request_uri";

    /**
     * The name of the request attribute that should be set by the container when custom error-handling servlet or JSP
     * page is invoked. The value of the attribute is of type {@code String}. See the chapter "Error Handling" in the
     * Servlet Specification for details.
     *
     * @since Servlet 3.0
     */
    String ERROR_SERVLET_NAME = "javax.servlet.error.servlet_name";

    /**
     * The name of the request attribute that should be set by the container when custom error-handling servlet or JSP
     * page is invoked. The value of the attribute is of type {@code java.lang.Integer}. See the chapter "Error
     * Handling" in the Servlet Specification for details.
     *
     * @since Servlet 3.0
     */
    String ERROR_STATUS_CODE = "javax.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.
     *
     * @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
     */
    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
     */
    void include(ServletRequest request, ServletResponse response) throws ServletException, IOException;
}
