RequestDispatcher (Servlet 4.0 API Documentation - Apache Tomcat 9.0.120)
Description: declaration: package: javax.servlet, interface: RequestDispatcher

# Interface RequestDispatcher

public interface RequestDispatcher
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.

See Also:
  - `ServletContext.getRequestDispatcher(String)`
  - `ServletContext.getNamedDispatcher(String)`
  - `ServletRequest.getRequestDispatcher(String)`

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final String`
  `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.
  `static final String`
  `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.
  `static final String`
  `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.
  `static final String`
  `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.
  `static final String`
  `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.
  `static final String`
  `ERROR_STATUS_CODE`
  The name of the request attribute that should be set by the container when custom error-handling servlet or JSP page is invoked.
  `static final String`
  `FORWARD_CONTEXT_PATH`
  The name of the request attribute that should be set by the container when the `forward(ServletRequest, ServletResponse)` method is called.
  `static final String`
  `FORWARD_MAPPING`
  The name of the request attribute that should be set by the container when the `forward(ServletRequest, ServletResponse)` method is called.
  `static final String`
  `FORWARD_PATH_INFO`
  The name of the request attribute that should be set by the container when the `forward(ServletRequest, ServletResponse)` method is called.
  `static final String`
  `FORWARD_QUERY_STRING`
  The name of the request attribute that should be set by the container when the `forward(ServletRequest, ServletResponse)` method is called.
  `static final String`
  `FORWARD_REQUEST_URI`
  The name of the request attribute that should be set by the container when the `forward(ServletRequest, ServletResponse)` method is called.
  `static final String`
  `FORWARD_SERVLET_PATH`
  The name of the request attribute that should be set by the container when the `forward(ServletRequest, ServletResponse)` method is called.
  `static final String`
  `INCLUDE_CONTEXT_PATH`
  The name of the request attribute that should be set by the container when the `include(ServletRequest, ServletResponse)` method is called on the `RequestDispatcher` obtained by a path and not by a name.
  `static final String`
  `INCLUDE_MAPPING`
  The name of the request attribute that should be set by the container when the `include(ServletRequest, ServletResponse)` method is called on the `RequestDispatcher` obtained by a path and not by a name.
  `static final String`
  `INCLUDE_PATH_INFO`
  The name of the request attribute that should be set by the container when the `include(ServletRequest, ServletResponse)` method is called on the `RequestDispatcher` obtained by a path and not by a name.
  `static final String`
  `INCLUDE_QUERY_STRING`
  The name of the request attribute that should be set by the container when the `include(ServletRequest, ServletResponse)` method is called on the `RequestDispatcher` obtained by a path and not by a name.
  `static final String`
  `INCLUDE_REQUEST_URI`
  The name of the request attribute that should be set by the container when the `include(ServletRequest, ServletResponse)` method is called on the `RequestDispatcher` obtained by a path and not by a name.
  `static final String`
  `INCLUDE_SERVLET_PATH`
  The name of the request attribute that should be set by the container when the `include(ServletRequest, ServletResponse)` method is called on the `RequestDispatcher` obtained by a path and not by a name.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `forward(ServletRequest request, ServletResponse response)`
  Forwards a request from a servlet to another resource (servlet, JSP file, or HTML file) on the server.
  `void`
  `include(ServletRequest request, ServletResponse response)`
  Includes the content of a resource (servlet, JSP page, HTML file) in the response.

- ## Field Details

  - ### FORWARD_REQUEST_URI

    static final String FORWARD_REQUEST_URI
    The name of the request attribute that should be set by the container when the `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
    See Also:
      - Constant Field Values

  - ### FORWARD_CONTEXT_PATH

    static final String FORWARD_CONTEXT_PATH
    The name of the request attribute that should be set by the container when the `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
    See Also:
      - Constant Field Values

  - ### FORWARD_MAPPING

    static final String FORWARD_MAPPING
    The name of the request attribute that should be set by the container when the `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 4.0
    See Also:
      - Constant Field Values

  - ### FORWARD_PATH_INFO

    static final String FORWARD_PATH_INFO
    The name of the request attribute that should be set by the container when the `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
    See Also:
      - Constant Field Values

  - ### FORWARD_SERVLET_PATH

    static final String FORWARD_SERVLET_PATH
    The name of the request attribute that should be set by the container when the `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
    See Also:
      - Constant Field Values

  - ### FORWARD_QUERY_STRING

    static final String FORWARD_QUERY_STRING
    The name of the request attribute that should be set by the container when the `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
    See Also:
      - Constant Field Values

  - ### INCLUDE_REQUEST_URI

    static final String INCLUDE_REQUEST_URI
    The name of the request attribute that should be set by the container when the `include(ServletRequest, ServletResponse)` method is called on the `RequestDispatcher` obtained by a path and not by a name. It provides information on the path that was used to obtain the `RequestDispatcher` instance for this include call. See the chapter "Included Request Parameters" in the Servlet Specification for details.
    Since:
      Servlet 3.0
    See Also:
      - Constant Field Values

  - ### INCLUDE_CONTEXT_PATH

    static final String INCLUDE_CONTEXT_PATH
    The name of the request attribute that should be set by the container when the `include(ServletRequest, ServletResponse)` method is called on the `RequestDispatcher` obtained by a path and not by a name. It provides information on the path that was used to obtain the `RequestDispatcher` instance for this include call. See the chapter "Included Request Parameters" in the Servlet Specification for details.
    Since:
      Servlet 3.0
    See Also:
      - Constant Field Values

  - ### INCLUDE_PATH_INFO

    static final String INCLUDE_PATH_INFO
    The name of the request attribute that should be set by the container when the `include(ServletRequest, ServletResponse)` method is called on the `RequestDispatcher` obtained by a path and not by a name. It provides information on the path that was used to obtain the `RequestDispatcher` instance for this include call. See the chapter "Included Request Parameters" in the Servlet Specification for details.
    Since:
      Servlet 3.0
    See Also:
      - Constant Field Values

  - ### INCLUDE_MAPPING

    static final String INCLUDE_MAPPING
    The name of the request attribute that should be set by the container when the `include(ServletRequest, ServletResponse)` method is called on the `RequestDispatcher` obtained by a path and not by a name. It provides information on the path that was used to obtain the `RequestDispatcher` instance for this include call. See the chapter "Included Request Parameters" in the Servlet Specification for details.
    Since:
      Servlet 4.0
    See Also:
      - Constant Field Values

  - ### INCLUDE_SERVLET_PATH

    static final String INCLUDE_SERVLET_PATH
    The name of the request attribute that should be set by the container when the `include(ServletRequest, ServletResponse)` method is called on the `RequestDispatcher` obtained by a path and not by a name. It provides information on the path that was used to obtain the `RequestDispatcher` instance for this include call. See the chapter "Included Request Parameters" in the Servlet Specification for details.
    Since:
      Servlet 3.0
    See Also:
      - Constant Field Values

  - ### INCLUDE_QUERY_STRING

    static final String INCLUDE_QUERY_STRING
    The name of the request attribute that should be set by the container when the `include(ServletRequest, ServletResponse)` method is called on the `RequestDispatcher` obtained by a path and not by a name. It provides information on the path that was used to obtain the `RequestDispatcher` instance for this include call. See the chapter "Included Request Parameters" in the Servlet Specification for details.
    Since:
      Servlet 3.0
    See Also:
      - Constant Field Values

  - ### ERROR_EXCEPTION

    static final String 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 `java.lang.Throwable`. See the chapter "Error Handling" in the Servlet Specification for details.
    Since:
      Servlet 3.0
    See Also:
      - Constant Field Values

  - ### ERROR_EXCEPTION_TYPE

    static final String 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 `java.lang.Class`. See the chapter "Error Handling" in the Servlet Specification for details.
    Since:
      Servlet 3.0
    See Also:
      - Constant Field Values

  - ### ERROR_MESSAGE

    static final String 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 `String`. See the chapter "Error Handling" in the Servlet Specification for details.
    Since:
      Servlet 3.0
    See Also:
      - Constant Field Values

  - ### ERROR_REQUEST_URI

    static final String 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 `String`. See the chapter "Error Handling" in the Servlet Specification for details.
    Since:
      Servlet 3.0
    See Also:
      - Constant Field Values

  - ### ERROR_SERVLET_NAME

    static final String 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 `String`. See the chapter "Error Handling" in the Servlet Specification for details.
    Since:
      Servlet 3.0
    See Also:
      - Constant Field Values

  - ### ERROR_STATUS_CODE

    static final String ERROR_STATUS_CODE
    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 `java.lang.Integer`. See the chapter "Error Handling" in the Servlet Specification for details.
    Since:
      Servlet 3.0
    See Also:
      - Constant Field Values

- ## Method Details

  - ### forward

    void forward(ServletRequest request, ServletResponse response) throws ServletException, IOException
    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.

    Parameters:
      `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:
      `ServletException` - if the target resource throws this exception
      `IOException` - if the target resource throws this exception
      `IllegalStateException` - if the response was already committed

  - ### include

    void include(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.

    Parameters:
      `request` - a `ServletRequest` object that contains the client's request
      `response` - a `ServletResponse` object that contains the servlet's response
    Throws:
      `ServletException` - if the included resource throws this exception
      `IOException` - if the included resource throws this exception