Java.Servlet.What is Request Dispatcher?

The RequestDispatcher is a Servlet API tool that lets you forward or include one web resource (like a servlet, JSP, or static file) from another servlet.

📦 What is RequestDispatcher?

It’s an interface in the javax.servlet package that allows one servlet to:

Action	Description
Forward	Transfer the request to another resource on the server, without the client knowing.
Include	Include the output of another resource in the current response.

RequestDispatcher dispatcher = request.getRequestDispatcher("target.jsp");

Or via the ServletContext:

RequestDispatcher dispatcher = getServletContext().getRequestDispatcher("/target.jsp");

🔁 Two Main Operations

1. Forward

Transfers control to another resource on the server, and terminates the current servlet.

request.getRequestDispatcher("/result.jsp").forward(request, response);

• URL does not change in the browser
• Request and response objects are shared
• Control does not return to the original servlet

➡️ Use case: Pass control after processing form data, like login or registration

2. Include

Includes the output of another resource into the current response.

request.getRequestDispatcher("/footer.jsp").include(request, response);

• Merges output
• Used for layouts, header/footer, etc.
• Original servlet keeps control

➡️ Use case: Composing pages with common headers/footers

🧪 Example: Forwarding to a JSP

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse res)
        throws ServletException, IOException {

    String name = req.getParameter("name");
    req.setAttribute("user", name);  // pass data

    RequestDispatcher dispatcher = req.getRequestDispatcher("/welcome.jsp");
    dispatcher.forward(req, res); // internally transfer
}

In welcome.jsp:

<h1>Welcome, ${user}</h1>

🧠 RequestDispatcher vs Redirect

Feature	RequestDispatcher.forward()	HttpServletResponse.sendRedirect()
Type	Server-side	Client-side
Browser URL changes?	❌ No	✅ Yes
Can share request data?	✅ Yes (setAttribute)	❌ No (requires session or params)
Control returns?	❌ No (after forward)	❌ No (new request entirely)
Use case	Internal workflow	Redirecting user elsewhere (e.g., login)

✅ Summary

Concept	Description
What is it?	Interface to forward or include resources
Where to get it?	request.getRequestDispatcher() or from context
Key methods	forward(), include()
Use cases	Layouts, controller-to-view transitions