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Servlet - web.xml Servlet - ServletContext Servlet - RequestDispatcher Servlet - Filters Servlet - Wrappers

Servlet - RequestDispatcher (forward and include)

📌 What You Will Learn

Understand the forward mechanism
Understand the include mechanism
Learn forward vs include vs sendRedirect differences
See complete working code examples

RequestDispatcher enables forwarding requests between servlets and including responses from other resources. This lesson covers forward, include, and Foreign RequestDispatcher with complete code examples.

Forward Mechanism

If Servlet-1 handles preliminary processing and Servlet-2 provides the complete response, use the forward mechanism.

Key points about forward:

The same request object is forwarded to the second servlet
Information sharing between components is possible via request-scoped attributes
SecondServlet has complete control on the response object — can change response headers
After committing the response, forward is not allowed (throws IllegalStateException)
Recursive forward calls cause StackOverflowError

Demo: Basic Forward

Example02

JCode Cell

1
2	import javax.servlet.*;
3	import javax.servlet.http.*;
4	import java.io.*;
5	import javax.servlet.annotation.*;
6	@WebServlet("/test1")
7	public class FirstServlet extends HttpServlet
8	{
9	public void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
10	{
11	PrintWriter out=resp.getWriter();
12	out.println("<h1>This is First Servlet</h1>");
13	RequestDispatcher rd = req.getRequestDispatcher("/test2");
14	rd.forward(req,resp);
15	}
16	}
17

Output


<h1>This is First Servlet</h1>

SecondServlet.java

Example03

JCode Cell

1
2	import javax.servlet.*;
3	import javax.servlet.http.*;
4	import java.io.*;
5	import javax.servlet.annotation.*;
6	@WebServlet("/test2")
7	public class SecondServlet extends HttpServlet
8	{
9
10	public void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
11	{
12	PrintWriter out=resp.getWriter();
13	out.println("<h1>This is Second Servlet</h1>");
14
15	}
16	}
17

Output


<h1>This is Second Servlet</h1>

Demo: Login Validation with Forward

login.html: Sends GET request with username and password

inbox.jsp: <h1>This is inbox page you can get all mail services</h1>

error.jsp: <h1>This is error page your credentials are invalid please login again here <a href="/advapps3D/login.html">LOGIN</a></h1>

login.html Form

Example05

JCode Cell

1
2	<h1> This is forward demo</h1>
3	<form action = "/advapps3D/test1" >
4	Enter Name :<input type=text name=uname><br>
5	Enter Password :<input type=text name=pwd><br>
6	<input type=submit>
7	</form>
8

ValidateServlet.java

Forward rules:

Case 1: Just before forwarding, the response is cleared — any response added by FirstServlet won't be displayed
Case 2: The same request object is forwarded — information sharing via request-scoped attributes is possible
Case 3: SecondServlet has complete control on the response object — can change headers added by FirstServlet
Case 4: After committing the response, forward is not allowed (throws IllegalStateException)
Case 5: Recursive forward calls always cause StackOverflowError

Example06

JCode Cell

1
2	import javax.servlet.*;
3	import javax.servlet.http.*;
4	import java.io.*;
5	import javax.servlet.annotation.*;
6	@WebServlet("/test1")
7	public class ValidateServlet extends HttpServlet
8	{
9	public void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
10	{
11	String name = req.getParameter("uname");
12	String pwd = req.getParameter("pwd");
13	if(name.equals("Durga") && pwd.equals("scwcd"))
14	{
15	ServletContext context=getServletContext();
16	RequestDispatcher rd =context.getRequestDispatcher("/inbox.jsp");
17	rd.forward(req,resp);
18	}
19	else
20	{
21	RequestDispatcher rd =req.getRequestDispatcher("/error.jsp");
22	rd.forward(req,resp);
23	}
24
25	}
26	}
27

Request Attributes Sharing

Sharing data via request attributes:

FirstServlet: req.setAttribute("count", 10);
SecondServlet: Object o = req.getAttribute("count");

Case 6: After forward, control returns to FirstServlet

Any remaining statements execute, but:

Writing to response is ignored by the web container
If an exception occurs, the exception info is displayed instead of SecondServlet's response
Only if all remaining statements execute successfully will SecondServlet's response be displayed

Example07

JCode Cell

1
2	public class FirstServlet extends HttpServlet
3	{
4	public void doGet(..)...
5	{
6	PrintWriter out=resp.getWriter();
7	RequestDispatcher rd=req.getRequestDispatcher("/test2");
8	rd.forward(req,resp);
9	System.out.println("After forward control comes back");// it will printed in the serverconsole
10	out.println("Hello this is FirstServlet again");//This line ignored by web container
11	System.out.println(10/0);// AE information will be displayed to the end user instead o
12	}
13	}
14

Forward Attributes Added by Web Container

While forwarding, the web container adds attributes to the request scope to make original request information available to the second servlet:

javax.servlet.forward.request_uri
javax.servlet.forward.context_path
javax.servlet.forward.servlet_path
javax.servlet.forward.path_info
javax.servlet.forward.query_string

Note: If RequestDispatcher is obtained via getNamedDispatcher(), no attributes are added.

Example08

JCode Cell

1
2	import javax.servlet.*;
3	import javax.servlet.http.*;
4	import java.io.*;
5	import java.util.*;
6	public class ForwardAttributeDemo extends HttpServlet
7	{
8
9	public void doGet(HttpServletRequest req,HttpServletResponse resp) throwsServletException,IOException
10	{
11	PrintWriter out = resp.getWriter();
12	out.println("<h1>Forward Request Attributes</h1>");
13	Enumeration e = req.getAttributeNames();
14	while(e.hasMoreElements())
15	{
16	String name= (String)e.nextElement();
17	Object value = req.getAttribute(name);
18	out.println(name+"....."+value+"<br>");
19	}
20	}
21	}
22

Include Mechanism

Use include to embed the response of other resources in the current response. Best suited for including banner information like copyright, logo, etc.

The servlet that receives the request initially is responsible for the response
After committing the response, you can perform include() but not forward()
In include, the second servlet does not have complete control on the response — it cannot change response headers

Demo: Include

Output: Hello This is FirstServlet → This is Second Servlet → Hi This is First Servlet again

Example10

JCode Cell

1
2	import javax.servlet.*;
3	import javax.servlet.http.*;
4	import java.io.*;
5	import javax.servlet.annotation.*;
6	@WebServlet("/test1")
7	public class FirstServlet extends HttpServlet
8	{
9	public void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
10	{
11	PrintWriter out=resp.getWriter();
12	out.println("<h1>Hello This is FirstServlet</h1>");
13	RequestDispatcher rd=req.getRequestDispatcher("/test2");
14	rd.include(req,resp);
15	out.println("<h1>Hi This is First Servlet again</h1>");
16	}
17	}
18

Output


<h1>Hello This is FirstServlet</h1>
<h1>Hi This is First Servlet again</h1>

SecondServlet.java (Include)

Include attributes added by web container:

javax.servlet.include.request_uri
javax.servlet.include.context_path
javax.servlet.include.servlet_path
javax.servlet.include.path_info
javax.servlet.include.query_string

Example11

JCode Cell

1
2	import javax.servlet.*;
3	import javax.servlet.http.*;
4	import java.io.*;
5	import javax.servlet.annotation.*;
6	@WebServlet("/test")
7	public class SecondServlet extends HttpServlet
8	{
9	public void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
10	{
11	PrintWriter out=resp.getWriter();
12	out.println("<h1>This is Second Servlet</h1>");
13	}
14	}
15

Output


<h1>This is Second Servlet</h1>

Foreign RequestDispatcher

To communicate with resources of other applications within the same server, use Foreign RequestDispatcher (FRD).

Example12

JCode Cell

1
2	import javax.servlet.*;
3	import javax.servlet.http.*;
4	import java.io.*;
5	import javax.servlet.annotation.*;
6	@WebServlet("/test1")
7	public class FirstServlet extends HttpServlet
8	{
9	public void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
10	{
11	ServletContext context=getServletContext();
12	ServletContext fc=context.getContext("/advapps3I");
13
14	RequestDispatcher rd=fc.getRequestDispatcher("/test2");
15	rd.forward(req,resp);
16	}
17	}
18

SecondServlet.java (Foreign RequestDispatcher)

Access at: http://localhost:7777/advapps3H/test1

Notes:

RequestDispatcher works only within the same server — both applications must be deployed on the same server
Most web servers don't support cross-context communication by default (security reasons) — throws NullPointerException
In Tomcat, add <Context crossContext="true"> in conf/context.xml
After committing the response, neither sendRedirect() nor forward() is allowed

Example13

JCode Cell

1
2	import javax.servlet.*;
3	import javax.servlet.http.*;
4	import java.io.*;
5	import javax.servlet.annotation.*;
6	@WebServlet("/test2")
7	public class SecondServlet extends HttpServlet
8	{
9	public void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
10	{
11	PrintWriter out=resp.getWriter();
12	out.println("<h1>This is Second Servlet..You can access by Foreign Request Dispatcher</h1>");
13	}
14	}
15

Output


<h1>This is Second Servlet..You can access by Foreign Request Dispatcher</h1>

Forward vs Include Comparison

Feature	forward()	include()
Purpose	Transfer control to another servlet for complete response	Include another servlet's response in current response
Responsible servlet	ForwardedServlet (S-2) provides complete response	IncludingServlet (S-1) is responsible for response
Call frequency	Only once, mostly as the last statement	Any number of times, no restrictions
Response control	SecondServlet has complete control on response object	IncludingServlet (S-1) has complete control
After commit	Not allowed (throws IllegalStateException)	Allowed
Use case	Servlets — processing logic (e.g., validate then forward to inbox)	JSPs — presentation logic (e.g., include header/footer)

Forward vs sendRedirect Comparison

Feature	forward()	sendRedirect()
Side	Server-side — client unaware of which servlet provides response	Client-side — client aware of which servlet provides response
Scope	Works only within the server	Works within or outside the server
Request object	Same request object forwarded — information sharing via request-scoped attributes	New request object created — no information sharing
Network	No extra trip to client — no network traffic or performance issues	Extra trip to client — increases network traffic and performance issues
Implementation	`rd.forward(req, resp)`	`resp.sendRedirect("url")`
Best for	Communicating within the server	Communicating outside the server

📝 Key Takeaways

Forward: server-side, one servlet transfers control to another
Include: embed another servlet's response in the current response
Request attributes for sharing data between servlets
Exam-style questions at the end

🧠 Test Your Knowledge

4 Questions

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Servlet

Nearby lessons

Servlet - RequestDispatcher (forward and include)

01Forward Mechanism

02Demo: Basic Forward

03SecondServlet.java

04Demo: Login Validation with Forward

05login.html Form

06ValidateServlet.java

07Request Attributes Sharing

08Forward Attributes Added by Web Container

09Include Mechanism

10Demo: Include

11SecondServlet.java (Include)

12Foreign RequestDispatcher

13SecondServlet.java (Foreign RequestDispatcher)

14Forward vs Include Comparison

15Forward vs sendRedirect Comparison

🧠 Test Your Knowledge

Forward Mechanism

Demo: Basic Forward

SecondServlet.java

Demo: Login Validation with Forward

login.html Form

ValidateServlet.java

Request Attributes Sharing

Forward Attributes Added by Web Container

Include Mechanism

Demo: Include

SecondServlet.java (Include)

Foreign RequestDispatcher

SecondServlet.java (Foreign RequestDispatcher)

Forward vs Include Comparison

Forward vs sendRedirect Comparison