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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 RequestDispatcher object,
 * which is used as a wrapper around a server resource located
 * at a particular path or given by a particular name.
 *
 * 

This interface is intended to wrap servlets, * but a servlet container can create RequestDispatcher * 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} */ static final String FORWARD_REQUEST_URI = "javax.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} */ static final String FORWARD_CONTEXT_PATH = "javax.servlet.forward.context_path"; /** * 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} */ static final String FORWARD_PATH_INFO = "javax.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} */ static final String FORWARD_SERVLET_PATH = "javax.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} */ static final String FORWARD_QUERY_STRING = "javax.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 */ static final String INCLUDE_REQUEST_URI = "javax.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 */ static final String INCLUDE_CONTEXT_PATH = "javax.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 */ static final String INCLUDE_PATH_INFO = "javax.servlet.include.path_info"; /** * The name of the request attribute under which the servlet path * of the target of an {@link #include(ServletRequest,ServletResponse) * include} is stored */ static final String INCLUDE_SERVLET_PATH = "javax.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 */ static final String INCLUDE_QUERY_STRING = "javax.servlet.include.query_string"; /** * The name of the request attribute under which the exception object * is propagated during an error dispatch */ public static final String ERROR_EXCEPTION = "javax.servlet.error.exception"; /** * The name of the request attribute under which the type of the * exception object is propagated during an error dispatch */ public static final String ERROR_EXCEPTION_TYPE = "javax.servlet.error.exception_type"; /** * The name of the request attribute under which the exception message * is propagated during an error dispatch */ public static final String ERROR_MESSAGE = "javax.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 */ public static final String ERROR_REQUEST_URI = "javax.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 */ public static final String ERROR_SERVLET_NAME = "javax.servlet.error.servlet_name"; /** * The name of the request attribute under which the response status * is propagated during an error dispatch */ public static final 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. * *

For a RequestDispatcher obtained via * getRequestDispatcher(), the ServletRequest * object has its path elements and parameters adjusted to match * the path of the target resource. * *

forward 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 IllegalStateException. * Uncommitted output in the response buffer is automatically cleared * before the forward. * *

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. * *

This method sets the dispatcher type of the given request to * DispatcherType.FORWARD. * * @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. * *

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. * *

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. * *

This method sets the dispatcher type of the given request to * DispatcherType.INCLUDE. * * @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; }





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