The RequestDispatcher interface in Java provides a way for a servlet to forward a request to another resource, such as another servlet or a JSP page, within the same web application. The forward method of the RequestDispatcher interface is used to accomplish this.

The RequestDispatcher interface is obtained through the getRequestDispatcher() method of the ServletContext or ServletRequest object. The method takes a String argument that specifies the URL pattern of the resource to which the request should be forwarded.

For example, the following code snippet shows how a servlet can forward a request to another servlet:

RequestDispatcher dispatcher = request.getRequestDispatcher("/servlet2");
dispatcher.forward(request, response);

In this example, the getRequestDispatcher() method is called with the URL pattern "/servlet2", which is the URL pattern of the servlet to which the request is being forwarded. The forward() method is then called on the dispatcher object, passing in the original request and response objects.

When the forward() method is called, the container stops processing the current request and forwards it to the specified resource. The specified resource can then generate a response, which is sent back to the client. Because the response is generated by the forwarded resource, it is not possible for the original servlet to modify the response.

The RequestDispatcher interface can also be used to include the output of another resource in the response of the current request. This is accomplished using the include() method of the RequestDispatcher interface, which has a similar signature to the forward() method.

In summary, the RequestDispatcher interface provides a powerful mechanism for servlets to forward requests to other resources, allowing for modular and reusable web application design.