What is a Request Dispatcher?

RequestDispatcher is an interface in the Java Servlet API used for forwarding a request to another resource (such as another servlet, JSP, or HTML file) within the same web application. It provides two methods: forward() and include().

Methods:

• forward(ServletRequest request, ServletResponse response):

  • Transfers complete control over the request and response to the specified resource.
  • The original servlet stops processing.
  • The URL in the browser's address bar does not change.
  • Used for fully delegating processing to another resource.

• include(ServletRequest request, ServletResponse response):

  • Includes the content of the specified resource in the response of the current servlet.
  • The original servlet continues execution after inclusion.
  • The URL in the browser's address bar does not change.
  • Allows multiple resources to participate in creating the response.

Obtaining a RequestDispatcher:

Can be obtained either from a ServletContext object or from a ServletRequest object.

• From ServletContext:

  // context path - path to another resource within the application
  RequestDispatcher rd = getServletContext().getRequestDispatcher("/anotherServlet");
  

• From ServletRequest:

  // relative path - relative path to another resource
  RequestDispatcher rd = request.getRequestDispatcher("/anotherServlet");
  

Differences between forward() and include():

Criterion	forward()	include()
Response control	Completely transferred to the target resource.	The response of the target resource is added to the current one.
Execution	The original servlet stops execution.	The original servlet continues execution.
URL	Does not change in the browser's address bar.	Does not change in the browser's address bar.
Usage	Delegating processing, redirection.	Including content, composing responses.

RequestDispatcher is an important tool for building complex web applications, allowing you to structure request processing logic and reuse components.