http://www.jboss.org/jboss-servlet-api_4.0_spec: The Java Servlet 4.0 API classes (JBoss by Red Hat) 
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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 Also:
/**
 * 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 forward 
/**
     * 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 forward 
/**
     * 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 HttpServletMapping is made available to the target of a forward 
Since:4.0
/**
     * The name of the request attribute under which the original
     * {@link javax.servlet.http.HttpServletMapping} is made available
     * to the target of a 
     * {@link #forward(ServletRequest,ServletResponse) forward}
     * 
     * @since 4.0
     */
    static final String FORWARD_MAPPING = "javax.servlet.forward.mapping";

    
The name of the request attribute under which the original path info is made available to the target of a forward 
/**
     * 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 forward 
/**
     * 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 forward 
/**
     * 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 
include is stored 
/**
     * 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 
include is stored 
/**
     * 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 
include is stored 
/**
     * 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 HttpServletMapping of the target of an 
include is stored 
/**
     * The name of the request attribute under which the
     * {@link javax.servlet.http.HttpServletMapping}
     * of the target of an {@link #include(ServletRequest,ServletResponse)
     * include} is stored
     */
    static final String INCLUDE_MAPPING = "javax.servlet.include.mapping";

    
The name of the request attribute under which the servlet path of the target of an 
include is stored 
/**
     * 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 
include is stored 
/**
     * 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

/**
     * 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

/**
     * 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

/**
     * 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

/**
     * 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

/**
     * 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

/**
     * 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 ServletRequestWrapper or ServletResponseWrapper classes that wrap them. 
This method sets the dispatcher type of the given request to
DispatcherType.FORWARD.

Params:
  • request – a ServletRequest object that represents the request the client makes of the servlet
  • response – a ServletResponse object that represents the response the servlet returns to the client
Throws:
See Also:
/**
     * 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.

The 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 ServletRequestWrapper or ServletResponseWrapper classes that wrap them. 
This method sets the dispatcher type of the given request to
DispatcherType.INCLUDE.

Params:
Throws:
See Also:
/**
     *
     * 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;
}