Τι είναι ο Request Dispatcher;

RequestDispatcher is an interface in the Java Servlet API, used to forward 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 full 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 to delegate processing entirely 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 RequestDispatcher:

Can be obtained either from the ServletContext object or from the 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	Fully transferred to the target resource.	The target resource's response is added to the current one.
Execution	The original servlet terminates 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, redirecting.	Including content, composing response.

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